Small Animal Dermatology PDF

CHAPTER | 3 Bacterial Skin Diseases Canine Pyoderma Subcutaneous Abscess (Cat and Dog Fight or Bite Pyotraumatic Dermatitis (Acute Moist Dermatitis, Abscess) Hot Spots)...

CHAPTER | 3 Bacterial Skin Diseases Canine Pyoderma Subcutaneous Abscess (Cat and Dog Fight or Bite Pyotraumatic Dermatitis (Acute Moist Dermatitis, Abscess) Hot Spots) Botryomycosis (Bacterial Pseudomycetoma, Impetigo (Superficial Pustular Dermatitis) Cutaneous Bacterial Granuloma) Superficial Pyoderma (Superficial Bacterial L-Form Infection Folliculitis) Actinomycosis Deep Pyoderma Nocardiosis Chin Pyoderma (Canine Acne) Opportunistic Mycobacteriosis (Atypical Skin Fold Dermatitis (Intertrigo, Skin Fold Mycobacterial Granuloma, Mycobacterial Pyoderma) Panniculitis) Mucocutaneous Pyoderma Feline Leprosy Syndrome Nasal Pyoderma (Nasal Folliculitis and Furunculosis) Canine Leproid Granuloma Syndrome (Canine Bacterial Pododermatitis Leprosy) Canine Pedal Furunculosis (Interdigital Bullae, Tuberculosis Interdigital Pyogranuloma) Plague Canine Pyoderma Pyoderma, a pyogenic cutaneous bacterial infection, is one of are classified as methicillin (synonymous with oxacillin) resis- the most common skin diseases of dogs. Although Staphylococ­ tant, signifying resistance to penicillins, cephalosporins, and cus pseudintermedius is the most prevalent bacterium recovered carbapenems. Often methicillin-resistant staphylococci (MRS) from canine pyoderma, other staphylococcal species have acquire resistance to other antimicrobials, too. In veterinary been isolated, including S. schleiferi, S. aureus, and S. lugdu­ medicine, MRS are becoming more common for reasons nensis. Pyoderma is almost always secondary to an underlying such as repeated systemic antibiotic exposure (especially fluo- disease process, mainly demodicosis, allergic skin disease, and roquinolones), subtherapeutic administration of systemic endocrinopathies (Box 3-1). Consequently, if the underlying antibiotics (dose or duration), long-term treatment with ste- cause is not identified and corrected, pyoderma will recur. roids, failure to identify and manage the underlying cause for Pyoderma tends to affect haired skin, repeatedly trauma- repeated infection, and patient contact with human health tized skin (e.g., pruritus, pressure points), body folds and care workers or facilities. creases, and skin of the trunk and often is distributed asym- Methicillin-resistant S. pseudintermedius (MRSP) is a poten- metrically on the body. Pruritus may or may not be a feature tial zoonosis, but human infections appear to be rare in of the clinical picture. Classification of disease is based on the healthy people; however, immunosuppressed people should depth of bacterial infection, which is associated with charac- be considered to have an elevated risk of infection from teristic lesions and recognized clinical presentations. Recogni- MRS. Transmission of methicillin-resistant S. aureus (MRS) is tion of the type of pyoderma (surface, superficial, or deep), mostly from human to pet (reverse zoonosis), but these along with cytologic confirmation of the presence of bacteria, animals may then be harboring a potential zoonosis. Given allows for a diagnosis and rudimentary treatment plan (Table the potential for (reverse) zoonosis, veterinarians must prac- 3-1). Empiric systemic antimicrobial therapy can then be tice good infection control practices with each case of pyo- prescribed, when needed, for the majority of first time epi- derma (e.g., washing hands, cleaning and disinfection), with sodes of pyoderma (Table 3-2). By far, superficial bacterial these measures enhanced when MRS has been documented in folliculitis (SBF) is the most common presentation of pyo- the patient (e.g., gloves, protective outerwear, separation of derma in dogs. MRS patient from rest of hospital patients). If family members Antimicrobial-resistant infections are emerging problems or people in close contact with the patient are immunosup- in health care. Staphylococci that have acquired the mecA gene pressed, the veterinarian should be aggressive in assessing the 45 46 CHAPTER 3 Bacterial Skin Diseases Canine Pyoderma—cont’d risk for zoonosis and contagion, culture the patient to identify BOX 3-1 Causes of Secondary Superficial and MRS, discuss isolating the patient from at-risk people, and Deep Pyoderma so on. Pyodermas caused by MRS are clinically indistinguishable Ectoparasitism (e.g., demodicosis, scabies, fleas) from susceptible opportunistic staphylococci. Therefore, the Allergic skin disease (e.g., flea hypersensitivity, patient’s history, in combination with clinical and cytological atopy, food allergy) findings, provide the clues suggestive of an antimicrobial- Endocrinopathy (e.g., hypothyroidism, resistant infection (Box 3-2). When evidence exists for one of hyperadrenocorticism, sex hormone imbalance) these infections, bacterial culture (including bacterial specia- Keratinization and seborrheic disorders tion) and susceptibility testing are indicated if systemic anti- Immunosuppressive therapy (e.g., glucocorticoids, biotics are thought to be warranted because of the extent and progestational compounds, cytotoxic severity of the pyoderma and inherent patient factors. After chemotherapy) MRS pyoderma is documented by culture, simple hygienic measures can be offered to the owner to help reduce fear Trauma (e.g., bite, penetrating wound, aggressively and enhance patient care (Box 3-3). At this time, routine scrubbing when bathing) screening for MRS in clinically healthy pets is not necessary or Follicular dysplasias (e.g., color dilution alopecia) recommended unless patient or human health implications Other skin diseases exist. Topical treatments for pyoderma include the use of anti- bacterial shampoos, mousses or foams, sprays, rinses, oint- ments, creams, gels, and wipes often with the active ingredients including, but not limited to, chlorhexidine 2% to 4% (also TABLE 3-1 Classification Scheme for Canine Pyoderma Depth of Infection or Characteristic Lesions Recognized Clinical Entities General Treatment Plan Pyoderma Surface: infection of the Erythema, surface exudate, Pyotraumatic dermatitis Often only requires topical therapy to most external skin layers crusts, erosions, intertrigo remove bacteria and excessive sebum excoriations, slightly raised until clinical resolution. plaques Topicals may be used as maintenance therapy when infection is controlled. Superficial: infection of Erythematous macules, Impetigo May only need sole topical therapy for follicular and interfollicular papules, pustules, crusted Superficial bacterial focal lesions. epithelium papules, scale, crusts, folliculitis If warranted, systemic antibiotics are epidermal collarettes, Superficial spreading prescribed for a minimum of 3 weeks erosions, excoriations, pyoderma (exfoliative and should be administered for 1 week hyperpigmentation, superficial pyoderma) beyond clinical resolution. lichenification, patchy Mucocutaneous pyoderma Adjunctive topical therapy hastens alopecia time to resolution. Highly antimicrobial-resistant infections need a combination of different topical treatments every 24–48 hours for 1 week beyond clinical resolution. Identifying the underlying cause will reduce the frequency of recurring pyoderma in the future. Deep: infection of the Nodules, plaques, furuncles, Deep pyoderma (nasal, chin, Systemic antibiotics should be selected dermis, subcutis, or hemorrhagic bullae, pressure point, pedal, and based off of a tissue culture deeper soft tissue fluctuant to firm soft tissue pyotraumatic) antibiogram with treatment continuing swelling, draining tracts, Postgrooming furunculosis for at least 2 weeks beyond clinical devitalized tissue, Cellulitis resolution (6–12+ weeks in total). gelatinous skin, ulcers, Acral lick dermatitis (lick Adjunctive topical therapy hastens necrosis, scarring alopecia, granuloma) time to resolution. hyperpigmentation, skin thickening  Canine Pyoderma 47 TABLE 3-2 Systemic Antimicrobial Therapy for BOX 3-2 Indications for Bacterial Skin Culture Bacterial Skin Infections First-Line Empiric Antimicrobial Therapy Human family member is immune compromised or immunosuppressed and at increased risk for Amoxicillin clavulanate 13–25 mg/kg PO q 8–12h zoonotic contagion of methicillin-resistant Cefadroxil 22 mg/kg PO q 8–12h staphylococci Cefpodoxime proxetil 5–10 mg/kg PO q 24h Failure to respond to appropriately prescribed systemic empiric therapy Cephalexin 30 mg/kg PO q 12h Deep lesions present (e.g., nodules and draining Cefovecin 8 mg/kg SC q 2wks tracts) Lincomycin 15–25 mg/kg PO q 12h Systemic antibiotics have been administered to patient within the past 30 days Ormetoprim– 55 mg/kg PO q 24h on day 1; sulfadimethoxine then 27.5 mg/kg PO q 24h Repeated courses of systemic antibiotics have been previously prescribed to the patient Trimethoprim–sulfadiazine 15–30 mg/kg PO q 12h or sulfamethoxazole Presence of recurring episodes of superficial pyoderma (e.g., papules, pustules, crusts, Second-Line Culture-Determined Antimicrobial Therapy collarettes, or patchy alopecia) Amikacin 15–30 mg/kg SC, IM, or IV q 24h Resistant bacterial infection (e.g., methicillin- Chloramphenicol 40–50 mg/kg PO q 8h resistant staphylococcal infection) previously diagnosed in the patient Clindamycin* 11 mg/kg PO q 12h An individual in the patient’s home has been Doxycycline 5–10 mg/kg PO q 12h diagnosed with methicillin-resistant Staphylococcus 10 mg/kg PO q 24h aureus or a resistant bacterial infection or an Enrofloxacin 10–20 mg/kg PO q 24h individual is a human health care worker or works in human health care facilities Gentamicin 9–14 mg/kg SC, IM, or IV q 24h Patient has been recently hospitalized or the Marbofloxacin 2.75–5.5 mg/kg PO q 24h patient has recently received an indwelling surgical Minocycline 10 mg/kg PO q 12h device Rod-shaped bacteria predominate on skin cytology Orbifloxacin 7.5 mg/kg PO q 24h from superficial or deep lesions Pradofloxacin 3 mg/kg PO q 24h Primary lesions (e.g., pustule, nodule) are the pre- Rifampin 5–10 mg/kg PO q 12–24h ferred lesions to culture. Purulent material can be aspi- rated from a pustule and transferred to a culturette. Last Resort Antimicrobial Therapy Deep nodules for culture are best obtained aseptically Linezolid Strongly discouraged because with an elliptical wedge biopsy. When necessary, cul- Teicoplanin these antibiotics are drugs of tures of the skin underneath adherent crusts or the Vancomycin last resort in humans. Consultation with a specialist expanding perimeter of an epidermal collarette can is recommended be swabbed with a culturette. The reference laboratory must be notified concerning the type of culture(s) *A D-test is required to determine clindamycin susceptibility in staphylococci that are resistant to erythromycin. requested (e.g., aerobic, anaerobic, mycobacterial, IM, Intramuscular; IV, intravenous; q, every; SC, subcutaneous. fungal). in combination with miconazole), benzoyl peroxide, ethyl lactate, bleach, and silver-containing products. In general, topical formulations that are not rinsed off will have a longer Glucocorticoid use is discouraged during treatment of the treatment effect. Given its routine use in human cases of MRS, pyoderma because it will alter the clinical picture to the owner topical mupirocin ointment should be avoided in canine MRS and veterinarian alike. If the dog is severely pruritic, oclacitinib pyoderma unless other topical treatments fail and there are no should be considered (3–7 days) over glucocorticoids. Regard- other suitable treatment options based on culture and suscep- less of the presence of methicillin resistance, patients should tibility testing. Although not antibacterial per se topical be reexamined near the end of the treatment schedule to ceramide creams may help improve the barrier function of the ensure clinical resolution of pyoderma or lack thereof. MRS skin, especially in atopic dogs, thereby limiting the chance for superficial pyoderma can usually be effectively treated with the infection reoccurrence. When systemic antibiotherapy is daily to every other day use of topical treatments and, when deemed necessary, then the correct antimicrobial possible, systemic antibiotics, but time to clinical resolution and dosage is to be prescribed (see Tables 3-1 and 3-2). may take longer for these infections. 48 CHAPTER 3 Bacterial Skin Diseases Canine Pyoderma—cont’d BOX 3-3 Simple Hygienic Recommendations for Owners of Dogs with Methicillin-Resistant Infections Keep young children and immune-compromised and Completely finish antibiotics as prescribed to your pet immunosuppressed people (cancer patients, HIV/ and return for follow-up examinations. If topical AIDS, patients receiving immunosuppressive drugs, treatments were prescribed, use them as diabetes) away from the affected pet. recommended, remembering to wash your hands Wear gloves when topically treating the affected pet’s after administration. wounds. Underlying medical or surgical conditions responsible Keep covered any open draining wounds on the for the bacterial infection must be sought and affected pet. managed for ultimate infection resolution (and Keep personal wounds covered and protected. prevention of relapse). Do not allow the affected pet to lick the face or Wash hands or use alcohol-based hand sanitizers after wounds of people. handling the affected pet and his or her bowls, cage, Do not share the same bed as the affected pet. and toys. Additionally, wash your hands before and Do not share towels or linens with the affected pet. after trips to the restroom. Remember everything your Regularly launder (detergent) and heat dry affected elders taught you about washing your hands (e.g., pet’s bedding. Separate bedding from human wash your hands before food preparation, use soap, clothing and linens. avoid splatter, gently scrub all surfaces of your hands Do not allow the affected pet to serve as a “therapy during the time it takes you to sing “Happy Birthday to animal” in human health care facilities. You” twice, dry your hands off ). In an attempt to limit the spread of infection, try to Regularly pick up stool (dogs) or scoop litterbox (cats) avoid pet daycare and public dog parks until the of the affected pet and dispose of it in the trash can. affected pet is cleared of the infection. For more information about using methicillin-resistant Consult with your personal physician if any in-contact Staphylococcus pseudintermedius and methicillin- people develop skin lesions or sores (e.g., pimples, resistant S. aureus keyword searches, see boils, swellings) or have concerns about your www.wormsandgermsblog.com, www.bsava.com, and personal health. www.thebellamossfoundation.com.  Pyotraumatic Dermatitis 49 Pyotraumatic Dermatitis (Acute Moist Dermatitis, Hot Spots) Features cream or solution should also be applied every 8 to 12 hours for 5 to 10 days. Pyotraumatic dermatitis is an acute and rapidly developing 6. If pruritus is severe, short-term oclacitinib (Apoquel) or surface bacterial skin infection that occurs secondary to self- steroids, such as injectable dexamethasone sodium phos- inflicted trauma. A lesion is created when the patient licks, phate (up to 0.1 mg/kg subcutaneous [SC] or intramuscu- chews, scratches, or rubs a focal area on its body in response lar [IM]) or prednisone (0.5–1 mg/kg oral [PO] should be to a pruritic or painful stimulus (Box 3-4). This usually is a administered every 24 hours for 5 to 10 days), may be seasonal problem that becomes more common when the helpful. weather is hot and humid. Fleas are the most common initiat- 7. If the central lesion is surrounded by papules or pustules, ing stimulus. Pyotraumatic dermatitis is common in dogs, systemic antibiotic therapy should also be instituted and especially in thick-coated, long-haired breeds. It is rarely seen continued for 3 to 4 weeks (see Table 3-2). in cats. 8. The prognosis is good if the underlying cause can be cor- Pyotraumatic dermatitis is an acutely pruritic, rapidly rected or controlled. enlarging area of erythema, alopecia, and weepy, eroded skin with well-demarcated margins. Lesions are usually single, but they may be multiple and often are painful. They occur most frequently on the trunk, tail base, lateral thigh, neck, and face. A spreading superficial pyoderma is often present. Top Differentials Differentials include superficial pyoderma, demodicosis, and dermatophytosis. Diagnosis 1. History, clinical findings; rule out other differentials 2. Cytology (impression smears): suppurative inflammation and mixed bacteria Treatment and Prognosis FIGURE 3-1 Pyotraumatic Dermatitis. This moist, erosive lesion on 1. The underlying cause (see Box 3-4) should be identified the base of the ear is characteristic of a hot spot. and treated. 2. Aggressive flea control should be provided. 3. The lesion should be clipped and cleaned, with the patient AUTHOR’S NOTE under sedation if necessary. Fluoroquinolone antibiotics may be indicated but 4. A topical drying agent or astringent (e.g., 5% aluminum likely increase the risk of methicillin resistance. acetate) should be applied every 8 to 12 hours for 2 to 7 days. Alcohol-containing products should be avoided. 5. If pruritus is mild, a topical analgesic (e.g., lidocaine, pramoxine hydrochloride) or corticosteroid-containing BOX 3-4 Causes of Pyotraumatic Dermatitis Fleas Other parasites (e.g., pediculosis, cheyletiellosis, scabies) Hypersensitivity (e.g., atopy, food, flea bite) Anal sac disease Otitis externa Folliculitis (e.g., bacterial, Demodex spp., dermatophytic) Trauma (e.g., minor wounds, foreign body) FIGURE 3-2 Pyotraumatic Dermatitis. Close-up of the dog in Figure Contact dermatitis 3-1. The moist, erosive surface of the lesion is apparent. The papular perimeter suggests an expanding superficial pyoderma. 50 CHAPTER 3 Bacterial Skin Diseases Pyotraumatic Dermatitis—cont’d FIGURE 3-3 Pyotraumatic Dermatitis. Close-up of a hot spot FIGURE 3-4 Pyotraumatic Dermatitis. An early superficial lesion (after demonstrating the erosive lesion with a moist serous exudate. clipping) on the lumbar region of a dog with flea allergy dermatitis. The papular perimeter suggests an expanding bacterial folliculitis. FIGURE 3-5 Pyotraumatic Dermatitis. This moist lesion developed acutely on the dorsum of this flea-allergic cat. FIGURE 3-6 Pyotraumatic Dermatitis. A severe erosive lesion with exudate on the ventral neck of a food-allergic cat.  Impetigo 51 Impetigo (Superficial Pustular Dermatitis) Features 3. Dermatohistopathology: nonfollicular subcorneal pus- tules that contain neutrophils and bacterial cocci Impetigo is a superficial bacterial infection of nonhaired skin 4. Bacterial culture: Staphylococcus organisms that may be associated with a predisposing disease or other underlying factors, such as endoparasitism, ectoparasitism, Treatment and Prognosis poor nutrition, or a dirty environment. It is commonly seen in young dogs before the time of puberty. 1. Any predisposing factors (poor hygiene and nutrition) Impetigo is characterized by small nonfollicular pustules, should be identified and corrected. papules, and crusts that are limited to the inguinal and axillary 2. Affected areas should be cleaned every 24 to 48 hours for skin. Lesions are not painful or pruritic. 7 to 10 days with an antibacterial shampoo that contains chlorhexidine. Top Differentials 3. If lesions are few in number, topical mupirocin or neomy- cin ointment or cream should be applied every 12 hours Differentials include demodicosis, superficial pyoderma, der- for 7 to 10 days. matophytosis, insect bites, and early scabies. 4. If lesions do not resolve with topical therapy, appropriate systemic antibiotics should be administered for 3 weeks, Diagnosis with treatment continued for 1 week beyond complete 1. Signalment, history, clinical findings; rule out other clinical resolution (see Table 3-2). differentials 5. The prognosis is good. 2. Cytology (pustule): neutrophils and bacterial cocci FIGURE 3-7 Impetigo. Numerous superficial pustules and crusts on FIGURE 3-8 Impetigo. More chronic lesions demonstrated by the abdomen of this puppy are typical of this disease. hyperpigmented macules on the abdomen of a puppy. Note that the papular dermatitis is still apparent. 52 CHAPTER 3 Bacterial Skin Diseases Superficial Pyoderma (Superficial Bacterial Folliculitis) Features Top Differentials Superficial pyoderma is a superficial bacterial infection involv- Differentials include demodicosis, dermatophytosis, scabies, ing hair follicles and the adjacent epidermis. The infection is and autoimmune skin diseases. almost always secondary to an underlying cause; allergies and endocrine disease are the most common causes (Box 3-5). Diagnosis Superficial pyoderma is one of the most common skin dis- 1. Rule out other differentials. eases in dogs but is rare in cats. 2. Cytology (pustule, skin impression): neutrophils and bac- Superficial pyoderma is characterized by focal, multifocal, terial cocci. or generalized areas of papules, pustules, crusts, scales, and/or 3. Dermatohistopathology: epidermal microabscesses, non- epidermal collarettes or circumscribed areas of erythema and specific superficial dermatitis, perifolliculitis, and folliculi- alopecia that may have hyperpigmented centers. Short-coated tis. Intralesional bacteria may be difficult to find. dogs often present with a “moth-eaten” patchy alopecia, small 4. Bacterial culture: Staphylococcus species. tufts of hair that stand up, or reddish brown discoloration of white hairs. These lesions are often mistaken for hives. In long-coated dogs, symptoms can be insidious and may include Treatment and Prognosis a dull, lusterless hair coat, scales, and excessive shedding. In 1. The underlying cause must be identified and controlled. both short- and long-coated breeds, primary skin lesions are 2. MRSP is a potential zoonosis, which is rapidly becoming often obscured by remaining hairs but can be readily appreci- a serious medical, ethical, and legal issue in veterinary ated if an affected area is clipped. Pruritus is variable, ranging medicine. Infections appear to be rare in healthy people; from none to intense levels. Bacterial infection secondary to however, immune incompetent people should be consid- endocrine disease may cause pruritus, thereby mimicking ered to have an elevated risk of infection from MRS. Trans- allergic skin disease. mission of MRS is mostly from human to pet (reverse S. pseudintermedius (previously Staphylococcus intermedius) is zoonosis), but these animals may then be harboring a the most common bacterium isolated from canine pyoderma potential zoonosis. Veterinarians must practice good infec- and is usually limited to dogs. S. schleiferi is a bacterial species tion control practices with each case of pyoderma (e.g., in dogs and humans that is emerging as a common canine washing hands, cleaning and disinfection), with these isolate in patients with chronic infection and previous antibi- measures enhanced when MRS has been documented in otic exposure. Both S. pseudintermedius and S. schleiferi may the patient (e.g., gloves, protective outerwear, separation develop methicillin resistance, especially if subtherapeutic of MRS patient from rest of hospital patients). If family doses of antibiotics or fluoroquinolone antibiotics have been members or people in close contact with the patient are used previously in the patient. Additionally, methicillin- immunocompromised, the veterinarian should be aggres- resistant Staphylococcus aureus (human MRS) is becoming sive in assessing the risk for zoonosis and contagion, more common among veterinary species. All three types of culture the patient to identify MRS, discuss isolating the Staphylococcus may be zoonotic, moving from human to canine patient from at-risk people, keep covered any open drain- or from canine to human; immunosuppressed individuals are ing wounds on the affected pet, keep personal wounds at greatest risk. covered and protected, do not allow the affected pet to lick the face or wounds of people, do not share the same bed as the affected pet, and do not share towels or linens with the affected pet. 3. Systemic antibiotics (minimum 3–4 weeks) should be administered and continued 1 week beyond complete BOX 3-5 Causes of Secondary Superficial and clinical and cytologic resolution (see Table 3-2). Deep Pyoderma 4. Concurrent bathing every 2 to 7 days with an antibacterial shampoo that contains chlorhexidine or benzoyl peroxide Demodicosis, scabies, Pelodera spp. is helpful. Hypersensitivity (e.g., atopy, food, flea bite) 5. If lesions recur within 7 days of antibiotic discontinuation, Endocrinopathy (e.g., hypothyroidism, the duration of therapy was inadequate and antibiotics hyperadrenocorticism, sex hormone imbalance) should be reinstituted for a longer time period; better Immunosuppressive therapy (e.g., glucocorticoids, attempts to identify and control the underlying disease progestational compounds, cytotoxic drugs) should be made. Autoimmune- and immune-mediated disorders 6. If lesions do not completely resolve during antibiotic Trauma or bite wound therapy or if the antibiotics produce no response, antibi- Other skin diseases otic resistance should be assumed and a bacterial culture and sensitivity submitted.  Superficial Pyoderma 53 7. If antibiotic resistance is suspected or confirmed, frequent can be stopped. Premature discontinuation of therapy, bathing (up to daily) and frequent application of topical inability to completely control the primary disease, and chlorhexidine solutions, combined with simultaneous the use of fluoroquinolone antibiotics will likely perpetu- administration of two different classes of antibiotics at ate the resistant infection. high doses, seem to produce the best results. Monitoring 8. The prognosis is good if the underlying cause can be iden- the infection with cytology and cultures with antibiotic tified and corrected or controlled. sensitivities is important for determining when treatments Distribution Pattern of Superficial Bacterial Folliculitis 54 CHAPTER 3 Bacterial Skin Diseases Superficial Pyoderma—cont’d FIGURE 3-9 Superficial Pyoderma. Alopecia, papules, and crusts FIGURE 3-10 Superficial Pyoderma. Papular rash on the abdomen of around the eye of this allergic Irish setter are typical of bacterial folliculitis. an allergic dog caused by multidrug-resistant Staphylococcus schleiferi. The papular rash typical of pyoderma persisted despite high-dose antibiotic therapy, suggesting the antibiotic-resistant nature of the organism. FIGURE 3-11 Superficial Pyoderma. Close-up of the papular rash in FIGURE 3-12 Superficial Pyoderma. This papular dermatitis forms Figure 3-10. coalescing lesions as demonstrated by the erythematous plaque. Note the early epidermal collarettes associated with some papules. AUTHOR’S NOTE Superficial pyoderma is one of the most common skin Daily baths and topical treatments can be very benefi- diseases in dogs and almost always has an underlying cial in resolving the infection. cause (allergies or endocrine disease). Maximize the dose of antibiotics, and consider using Cefpodoxime, ormetoprim–sulfadimethoxine (Primor), two antibiotics simultaneously to prevent additional and Convenia provide the most consistent compliance; resistance from developing. therefore, they seem to help reduce the development of Practice good hygiene (hand washing) to prevent resistance when used at high doses. zoonosis. MRS, MRSS, and MRSP are emerging problems in Consider screening dogs that visit older or sick people some regions of the United States. to prevent zoonosis. Cultures from the nose, lips, ears, The most likely risk factors include previous exposure axilla, and perianal areas are best for screening patients to fluoroquinolone antibiotics, subtherapeutic antibiotic for MRS. dosing, and concurrent steroid therapy. Text continued on p. 60  Superficial Pyoderma 55 FIGURE 3-13 Superficial Pyoderma. Severe erythematous dermatitis FIGURE 3-14 Superficial Pyoderma. Close-up of the dog in Figure with large epidermal collarettes caused by a multidrug-resistant 3-13. Erythematous dermatitis with epidermal collarettes formation is infection. apparent. FIGURE 3-15 Superficial Pyoderma. More typical epidermal FIGURE 3-16 Superficial Pyoderma. This moth-eaten texture of the collarettes in a dog with resolving pyoderma. hair coat is a characteristic finding in short-coated breeds with pyoderma. FIGURE 3-17 Superficial Pyoderma. The moth-eaten alopecia is FIGURE 3-18 Superficial Pyoderma. Focal papules and crusts caused typical of pyoderma in short-coated breeds. by pyoderma can be hidden by a dense fur coat. A window was clipped within the fur coat to reveal these lesions. 56 CHAPTER 3 Bacterial Skin Diseases Superficial Pyoderma—cont’d FIGURE 3-19 Superficial Pyoderma. This large focal area of alopecia, FIGURE 3-20 Superficial Pyoderma. Partial alopecia and mild papular erythema, and hyperpigmentation with central regrowth of hair is often rash on the foreleg of this dog were caused by secondary bacterial misdiagnosed as dermatophytosis. folliculitis associated with hypothyroidism. FIGURE 3-21 Superficial Pyoderma. This focal area of lichenification FIGURE 3-22 Superficial Pyoderma. Alopecic dermatitis with a with adherent crust formation on the upper lip of a dog responded to purulent exudate on the lip of a dog. Note how the dog’s normal topical mupirocin therapy. (Courtesy of L. Frank.) pigmentation masks the papular dermatitis. FIGURE 3-23 Superficial Pyoderma. Crusting papular dermatitis FIGURE 3-24 Superficial Pyoderma. Papular crusting dermatitis with caused matting of the hair in this medium-haired dog. In thick-coated alopecia on the muzzle of a dog. breeds, it may be difficult to see the underlying cutaneous lesions.  Superficial Pyoderma 57 FIGURE 3-25 Superficial Pyoderma. Multifocal, punctate lesions on FIGURE 3-26 Superficial Pyoderma. Focal area of alopecia caused by the dorsum are a typical feature of postbathing folliculitis and folliculitis in an allergic dog. Cutaneous cytology is necessary. furunculosis. FIGURE 3-27 Superficial Pyoderma. Erythema caused by secondary FIGURE 3-28 Superficial Pyoderma. Multiple papules, crusts, and infection in an allergic dog. The lesion is indistinguishable from a epidermal collarettes in a dog with hypothyroidism. Demodex, dermatophyte, or yeast infection. FIGURE 3-29 Superficial Pyoderma. Close-up of the dog in Figure FIGURE 3-30 Superficial Pyoderma. Severe papular rash with crusting 3-28. Papular rash with crusting is apparent. dermatitis in an allergic dog. 58 CHAPTER 3 Bacterial Skin Diseases Superficial Pyoderma—cont’d FIGURE 3-31 Superficial Pyoderma. An unusual pyoderma lesion on FIGURE 3-32 Superficial Pyoderma. Severe erythematous dermatitis the head of a dog with allergies. without the typical papular, crusting rash, which is more typical of pyoderma. FIGURE 3-33 Superficial Pyoderma. Same dog as in Figure 3-32. FIGURE 3-34 Superficial Pyoderma. Atypically shaped erythematous Erythematous macular lesions without a papular rash are apparent. lesions in an allergic dog. Cutaneous cytology identified cocci, and the patient responded to oral antibiotics administered for 3 weeks. FIGURE 3-35 Superficial Pyoderma. Generalized dermatitis in an FIGURE 3-36 Superficial Pyoderma. Severe inflammation caused by allergic dog. The severe inflammation is similar to staphylococcal scalded secondary bacterial infection. Comedones and pustules are visible. skin syndrome in humans.  Superficial Pyoderma 59 FIGURE 3-37 Superficial Pyoderma. Papular rash with epidermal FIGURE 3-38 Superficial Pyoderma. Severe erythematous lesions collarettes typical of folliculitis in an allergic dog. associated with an aggressive bacterial infection. FIGURE 3-39 Superficial Pyoderma. Focal pustule associated with a FIGURE 3-40 Superficial Pyoderma. Severe crusting bacterial developing bacterial infection. infection typical of chronic and recurrent bacterial infections. 60 CHAPTER 3 Bacterial Skin Diseases Deep Pyoderma Features 4. Bacterial culture: primary pathogen is usually Staphylococcus, but occasionally, Pseudomonas is isolated. Mixed gram-positive Deep pyoderma is a surface or follicular bacterial infection and gram-negative bacterial infections are also common. that breaks through hair follicles to produce furunculosis and cellulitis. Its development is often preceded by a history of chronic superficial skin disease, and it is almost always associ- Treatment and Prognosis ated with some predisposing factor (see Box 3-5). Deep pyo- 1. Any underlying cause should be identified and corrected derma is common in dogs and rare in cats. (see Box 3-5). S. pseudintermedius (previously S. intermedius) is the most 2. MRSP is a potential zoonosis, which is rapidly becoming a common bacterium isolated from canine pyoderma and is serious medical, ethical, and legal issue in veterinary medi- usually limited to dogs. S. schleiferi is a bacterial species in cine. Infections appear to be rare in healthy people; however dogs and humans that is emerging as a common canine isolate immune incompetent people should be considered to have in patients with chronic infection and previous antibiotic an elevated risk of infection from MRS. Transmission of exposure. Both S. pseudintermedius and S. schleiferi may develop MRS is mostly from human to pet (reverse zoonosis), but methicillin resistance, especially if subtherapeutic doses of these animals may then be harboring a potential zoonosis. antibiotics or fluoroquinolone antibiotics have been used pre- Veterinarians must practice good infection control prac- viously in the patient. Additionally, human MRS is becoming tices with each case of pyoderma (e.g., washing hands, more common among veterinary species. All three types of cleaning and disinfection), with these measures enhanced Staphylococcus may be zoonotic, moving from human to canine when MRS has been documented in the patient (e.g., or from canine to human; immunosuppressed individuals are gloves, protective outerwear, separation of MRS patient at greatest risk. from rest of hospital patients). If family members or people Deep pyoderma manifests as focal, multifocal, or general- in close contact with the patient are immunocompromised, ized skin lesions characterized by papules, pustules, cellulitis, the veterinarian should be aggressive in assessing the risk tissue discoloration, alopecia, hemorrhagic bullae, erosions, for zoonosis and contagion, culture the patient to identify ulcers, and crusts, as well as serosanguineous to purulent MRS, discuss isolating the patient from at-risk people, keep draining fistulous tracts. Lesions are often pruritic or painful. covered any open draining wounds on the affected pet, They most often involve the trunk and pressure points but keep personal wounds covered and protected, do not allow can appear anywhere on the body. Lymphadenomegaly is the affected pet to lick the face or wounds of people, do not common. If the animal is also septic, other symptoms include share the same bed as the affected pet, and do not share fever, anorexia, and depression. towels or linens with the affected pet. Postgrooming furunculosis is a newly recognized acute- 3. Crusts should be loosened and exudate removed with onset deep pyoderma that occurs within days of water immer- daily warm water soaks or whirlpool baths that contain a sion or exposure to grooming products (e.g., shampoo, chlorhexidine solution. If tub soaks are not possible, brushing). Erythematous maculopapules, pustules, furuncles, shampoo therapy may be effective. hemorrhagic crusts, tiny ulcers, and draining tracts dorsally 4. Systemic antibiotics should be administered over the long distributed on the neck and trunk are typical. Lethargy, fever, term (minimum 6–8 weeks) and should be continued 2 and pain along lesional skin are frequently encountered. Pseu­ weeks beyond complete clinical resolution (see Table 3-2). domonas aeruginosa appears to be the most common isolate, Antibiotics should be selected on the basis of in vitro but bacterial culture and susceptibility testing should be per- sensitivity results because resistance is common. formed to document the pathogen and to assist in medical 5. If lesions do not completely resolve during antibiotic treatment. therapy or if the antibiotics produce no response, antibi- otic resistance should be assumed, and a bacterial culture Top Differentials and sensitivity submitted. 6. If antibiotic resistance is suspected or confirmed, frequent Differentials include demodicosis, fungal infection, actinomy- bathing (up to daily) and frequent application of topical cosis, nocardiosis, mycobacteriosis, neoplasia, and autoim- chlorhexidine solutions, combined with simultaneous mune skin disorders. administration of two different classes of antibiotics at high doses, seem to produce the best results. Monitoring Diagnosis the infection with cytology and cultures with antibiotic 1. Rule out other differentials. sensitivities is important for determining when treatments 2. Cytology (impression smears, exudate): suppurative to can be stopped. Premature discontinuation of therapy, pyogranulomatous inflammation with bacterial cocci or inability to completely control the primary disease, and rods. use of fluoroquinolone antibiotics will likely perpetuate 3. Dermatohistopathology: deep suppurative to pyogranulo- the resistant infection. matous folliculitis, furunculosis, cellulitis, and panniculi- 7. The prognosis is good, but in severe or chronic cases, tis. Intralesional bacteria may be difficult to find. fibrosis, scarring, and alopecia may be permanent sequelae.  Deep Pyoderma 61 FIGURE 3-41 Deep Pyoderma. Purulent exudate from a deep FIGURE 3-42 Deep Pyoderma. Patchy alopecia with focal crusted ulcerative lesion and draining tract. lesions covering ulcers and draining tracts. Note that deep pyoderma (cellulitis) affects a large region of skin, rather than discrete papules or pustules typical of superficial pyoderma. FIGURE 3-43 Deep Pyoderma. This focal area of alopecia and FIGURE 3-44 Deep Pyoderma. This aggressive bacterial infection was lichenification demonstrates an ulcer and draining tract typical of deep causing necrosis of large sections of skin, suggestive of necrotizing pyoderma. Note that lichenification is caused by the chronicity of the fasciitis. Numerous bacterial species, including methicillin-resistant lesion. Staphylococcus aureus, were isolated on culture. 62 CHAPTER 3 Bacterial Skin Diseases Deep Pyoderma—cont’d FIGURE 3-45 Deep Pyoderma. Diffuse erythematous dermatitis of the FIGURE 3-46 Deep Pyoderma. Severe interdigital dermatitis (alopecia, foot. The medial digit is the site of previous surgery; it subsequently erythema, lichenification) with a moist exudate and draining tract typical became infected with Pseudomonas. Note that dermatitis of surrounding of deep pyoderma. tissue is caused by opportunistic infection at the surgical site. FIGURE 3-47 Deep Pyoderma. Severe lichenification and cellulitis caused by chronic bacterial infections. FIGURE 3-48 Deep Pyoderma. Deep multifocal cellulitis on the dorsum of a dog with postbathing folliculitis and furunculosis.  Chin Pyoderma 63 Chin Pyoderma (Canine Acne) Features (minimum 4–6 weeks) and continued 2 weeks beyond complete clinical and cytologic resolution (see Table 3-2). Chin pyoderma is a bacterial infection that is not true acne 5. Adhesive tape (Elasticon) can be used to tape strip the but rather is a traumatic furunculosis. Short, stiff hairs are “ingrown” hairs, making hair removal both easy and fun. forced backward through the hair follicle, creating a sterile 6. The prognosis is good. In many dogs, the lesions resolve foreign body reaction that may become subsequently infected. permanently; however, some dogs require lifelong routine This may be induced by trauma to the chin (e.g., caused by topical therapy for control. lying on hard floors, friction from chew toys). Chin pyoderma is common in short-coated breed dogs, especially when young (3- to 12-month-old). Chin pyoderma manifests as nonpainful and nonpruritic AUTHOR’S NOTE comedones, papules, pustules, and bullae or as ulcerative The cause of chin pyoderma is unknown, but focus- draining tracts with serosanguineous discharge on the chin or ing on removing the “ingrown” hairs seems to work muzzle. Often hair can be expressed from the lesions when well in preventing recurrence; however, active gently squeezed. infections should be treated both topically and Top Differentials orally. Interdigital bullae may have a similar under- lying pathology. Differentials include demodicosis, dermatophytosis, early juvenile cellulitis, and contact dermatitis. Diagnosis 1. Signalment, history, clinical findings; rule out other differentials. 2. Cytology (pustules, exudate, skin impression smear): sup- purative inflammation and bacterial cocci. 3. Dermatohistopathology: follicular hyperkeratosis, follicu- litis, or furunculosis. Intralesional bacteria may be difficult to find. 4. Bacterial culture: primary pathogen is usually Staphylococ­ cus. Mixed bacterial infections are possible. Treatment and Prognosis 1. Trauma and pressure to the chin should be minimized. 2. For mild lesions, the area should be scrubbed with benzoyl peroxide or chlorhexidine shampoo in the direction of hair growth. This mechanical scrubbing to remove “ingrown” hairs is important for preventing future lesions and speeding resolution. 3. Mupirocin ointment or benzoyl peroxide gel should be applied every 24 hours until lesions resolve, then every 3 to 7 days, as needed for control. 4. For moderate to severe lesions, in addition to topical FIGURE 3-49 Chin Pyoderma. Erythematous papular lesions with treatment, systemic antibiotics should be administered alopecia on the chin of an English bulldog. 64 CHAPTER 3 Bacterial Skin Diseases Chin Pyoderma—cont'd FIGURE 3-52 Chin Pyoderma. Severe papular crusting dermatitis with alopecia. Note that the purulent exudate suggests a deep infection. FIGURE 3-50 Chin Pyoderma. Alopecic papular dermatitis on the chin. Note the large dilated follicles associated with each papule. FIGURE 3-53 Chin Pyoderma. Severe papular dermatitis with alopecia FIGURE 3-51 Chin Pyoderma. Mild erythematous papular lesions on the chin and upper lip. with alopecia on the chin of an English bulldog.  Skin Fold Dermatitis 65 Skin Fold Dermatitis (Intertrigo, Skin Fold Pyoderma) Features Treatment and Prognosis Skin fold dermatitis is a common bacterial surface skin infec- 1. A weight reduction program should be initiated if the dog tion that occurs in dogs with excessive skin folds. Infection is obese. involves the facial folds of brachycephalic breeds, the lip folds 2. Cleansing wipes (i.e., alcohol-free acne pads, baby wipes, of dogs with large lip flaps, the tail folds of brachycephalic chlorhexidine-containing pledgets, other antimicrobial breeds with “corkscrew” tails, the vulvar folds of females with wipes) used every 12 to 72 hours work very well. small recessed vulvas, and the body folds of dogs with exces- 3. Alternatively, routine topical therapy can be used to control sive trunk or leg folds. Obesity is a common contributing the skin problem. For facial, tail, lip, or vulvar fold derma- factor; when addressed, the severity and recurrence of skin fold titis, the affected area should be cleaned every 1 to 3 days dermatitis are often improved. as needed with an antibacterial shampoo that contains Facial fold dermatitis: nonpainful, nonpruritic, erythematous chlorhexidine, benzoyl peroxide, or ethyl lactate. facial folds that may also be malodorous. Concurrent trau- 4. Topical application of an antibiotic cream, ointment, solu- matic keratitis or corneal ulceration is common. tion, or spray every 24 hours for the first 5 to 7 days of Lip fold dermatitis: fetid breath caused by saliva accumulat- therapy may be helpful. ing in macerated, erythematous lower lip fold(s) is usually 5. Any concurrent disease (e.g., corneal ulcers, dental disease, the presenting complaint. Concurrent dental calculi, gin- gingivitis, urinary tract infection) should be treated. givitis, and excessive salivation may contribute to the 6. Surgical excision of excess facial, lip, or vulvar folds or tail halitosis. amputation for tail fold dermatitis is usually curative. Tail fold dermatitis: skin under the tail is macerated, ery- 7. Prognosis is good, but lifelong topical maintenance therapy thematous, and malodorous. may be needed if surgical correction is not performed. Vulvar fold dermatitis: symptoms include erythematous, macerated, and malodorous vulvar folds, excessive vulvar licking, and painful urination. A secondary urinary tract infection may be present, causing the skin fold infection (descending) or resulting from the urinary tract infection (ascending). Body fold dermatitis: erythematous, seborrheic, often mal- odorous and sometimes mildly pruritic truncal or leg folds. Top Differentials Differentials include superficial pyoderma, Malassezia derma- titis, demodicosis, and dermatophytosis. Vulvar fold dermati- tis also includes urine scald or primary cystitis or vaginitis. Diagnosis 1. Signalment, history, clinical findings; rule out other differentials 2. Cytology (impression smears): presence of mixed bacteria and possibly yeast 3. Urinalysis (cystocentesis): bacteriuria in dogs with vulvar fold dermatitis that have a secondary urinary tract FIGURE 3-54 Skin fold dermatitis. A Shar Pei with its distinctive infection wrinkles that predispose this breed to skin fold dermatitis. 66 CHAPTER 3 Bacterial Skin Diseases Skin Fold Dermatitis—cont’d FIGURE 3-55 Skin Fold Dermatitis. A mature Boxer with a deep facial FIGURE 3-56 Skin Fold Dermatitis. Close-up of the dog in Figure 3-55. skin fold. Dermatitis was not apparent until the skin fold was examined. The skin fold was retracted, revealing a moist, erythematous dermatitis. FIGURE 3-57 Skin Fold Dermatitis. A mature golden retriever with FIGURE 3-58 Skin Fold Dermatitis. Close-up of the dog in Figure 3-57. vulvar fold dermatitis. Dermatitis was not apparent until the skin fold The skin fold was retracted, revealing a moist, severely erosive dermatitis. was retracted. FIGURE 3-59 Skin Fold Dermatitis. Lip fold dermatitis. The inflamed FIGURE 3-60 Skin Fold Dermatitis. Same dog as in Figure 3-59. The lip lesion is not apparent until the fold is retracted. fold has been retracted, revealing moist, erosive dermatitis caused by the superficial bacterial infection.  Skin Fold Dermatitis 67 FIGURE 3-61 Skin Fold Dermatitis. Perivulvar dermatitis caused by FIGURE 3-62 Skin Fold Dermatitis. Same dog as in Figure 3-61. The superficial bacteria and yeast. perivulvar tissue has been retracted, revealing the large area of alopecic, erythematous, lichenified skin. This dermatitis was caused by superficial bacterial and yeast infection. FIGURE 3-63 Skin Fold Dermatitis. A mature English bulldog with tail FIGURE 3-64 Skin Fold Dermatitis. Tail fold dermatitis. fold dermatitis. The deep skin folds associated with the tail of this breed are common sites for infection. 68 CHAPTER 3 Bacterial Skin Diseases Mucocutaneous Pyoderma Features infiltrates often are predominantly composed of plasma cells, with varying numbers of lymphocytes, neutrophils, Mucocutaneous pyoderma is a bacterial infection of mucocu- and macrophages. taneous junctions. It is uncommon in dogs; German shep- herds and their crosses are possibly predisposed, indicating Treatment and Prognosis possible association with the ulcerative syndromes of German shepherds (mucocutaneous pyoderma, perianal fistula, meta- 1. For mild to moderate lesions, affected areas should tarsal ulceration). be clipped and cleaned with shampoo that contains Lesions are characterized by mucocutaneous swelling, chlorhexidine. erythema, and crusting, often bilateral and sometimes sym- 2. Topical mupirocin ointment or cream should be applied metrical. Affected areas may be painful or pruritic and self- every 12 to 24 hours for 1 week and then every 3 to 7 days traumatized; they may become exudative, eroded, ulcerated, for maintenance therapy as needed. fissured, and depigmented. The margins of the lips, especially 3. For severe lesions, in addition to topical therapy, appropri- at the commissures, are most frequently affected. ate systemic antibiotics should be administered for 3 to 6 weeks (see Table 3-2). Top Differentials 4. Prognosis is good if an underlying primary disease (e.g., allergy, endocrinopathy) can be identified and controlled, Differentials include superficial pyoderma, lip fold dermatitis, but lifelong maintenance therapy is often needed. If regu- autoimmune skin disorders, demodicosis, dermatophyto- larly applied, topical antibiotics may maintain remission. sis, Malassezia dermatitis, candidiasis, and epitheliotropic lymphoma. AUTHOR’S NOTE Diagnosis Mucocutaneous pyoderma must be differentiated from DLE as both appear clinically similar and can 1. History, clinical findings; rule out other differentials. have similar histopathology changes. 2. Cytology (impression smear): bacterial cocci or rods. This syndrome may be so painful that systemic 3. Dermatohistopathology: epidermal hyperplasia, superfi- antibiotics are more beneficial compared with cial epidermal pustules, crusting, and lichenoid dermatitis topical antibacterial therapy. with preservation of basement membrane. Dermal Distribution Pattern of Mucocutaneous Pyoderma  Mucocutaneous Pyoderma 69 FIGURE 3-65 Mucocutaneous Pyoderma. The acute perioral FIGURE 3-66 Mucocutaneous Pyoderma. Alopecia is the principal dermatitis in this terrier was intensely pruritic. Alopecia, erythema, and lesion in this German shepherd with perioral dermatitis. erosions are visible around the mucocutaneous junction. FIGURE 3-67 Mucocutaneous Pyoderma. This erythematous FIGURE 3-68 Mucocutaneous Pyoderma. Erythematous, alopecic dermatitis with crusts was caused by a concurrent bacterial and dermatitis with a moist exudate predominantly on the lower lip. Malassezia dermatitis. FIGURE 3-69 Mucocutaneous Pyoderma. Severe ulcerative cellulitis on the mucocutaneous junctions of a dog. As the disease becomes more severe, the lesions expand laterally and develop erosions and ulcers. 70 CHAPTER 3 Bacterial Skin Diseases Nasal Pyoderma (Nasal Folliculitis and Furunculosis) Features Diagnosis Nasal pyoderma is a facial bacterial skin infection that may 1. Rule out other differentials. occur secondary to trauma or insect bites. This disease may be 2. Cytology (exudate, impression smear): suppurative inflam- closely associated with eosinophilic furunculosis in that both mation with bacterial cocci or rods. disorders have very similar clinical progression and appear- 3. Dermatohistopathology: perifolliculitis, folliculitis, furun- ance. It is uncommon in dogs and rare in cats. culosis, or cellulitis. Intralesional bacteria may be difficult Nasal pyoderma appears as papules, pustules, erythema, to find. alopecia, crusting, swelling, erosions, or ulcerative fistulae that 4. Bacterial culture: primary pathogen is usually Staphylococ­ develop over the bridge of the nose. Lesions may be painful. cus, but mixed bacterial infections are also common. Top Differentials Treatment and Prognosis Differentials include eosinophilic furunculosis of the face 1. Gentle, topical, warm water soaks with a chlorhexidine (dog), demodicosis, dermatophytosis, autoimmune skin dis- shampoo should be used every 24 hours for 7 to 10 days orders, dermatomyositis, nasal solar dermatitis, and mosquito to remove crusts. bite hypersensitivity (cat). 2. Systemic antibiotics should be administered (minimum 3–6 weeks) and continued 2 weeks beyond complete clini- cal resolution (see Table 3-2). 3. The prognosis is good, but scarring may be a permanent sequela in some dogs. FIGURE 3-70 Nasal Pyoderma. Erythematous papular rash with FIGURE 3-71 Nasal Pyoderma. Alopecia, erythema, and papular alopecia on the dorsal nose. Note that the lesions are on haired skin, swelling on the bridge of a dog’s nose. Note the similarity to eosinophilic unlike autoimmune skin disease, which affects the nasal planum. furunculosis of the face. (Courtesy of D. Angarano.)  Bacterial Pododermatitis 71 Bacterial Pododermatitis Features however, immune incompetent people should be consid- ered to have an elevated risk of infection from MRS. Trans- Bacterial pododermatitis is a deep bacterial infection of the mission of MRS is mostly from human to pet (reverse feet that almost always occurs secondary to some underlying zoonosis), but these animals may then be harboring a factor (Box 3-6). It is common in dogs and rare in cats. potential zoonosis. Veterinarians must practice good infec- One or more feet may be affected by interdigital erythema, tion control practices with each case of pyoderma (e.g., pustules, papules, nodules, hemorrhagic bullae, fistulae, washing hands, cleaning and disinfection), with these ulcers, alopecia, or swelling. Pruritus (licking, chewing), pain, measures enhanced when MRS has been documented in or lameness may be present. Regional lymphadenomegaly is the patient (e.g., gloves, protective outerwear, separation common. Occasionally, pitting edema of the associated meta- of MRS patient from rest of hospital patients). If family tarsus or metacarpus is seen. Lesions spontaneously resolve, members or people in close contact with the patient are wax and wane, or persist indefinitely. immunocompromised, the veterinarian should be aggres- sive in assessing the risk for zoonosis and contagion, Top Differentials culture the patient to identify MRS, discuss isolating the Differentials include demodicosis, Malassezia pododermatitis, patient from at-risk people, keep covered any open drain- dermatophytosis, actinomycosis, nocardiosis, mycobacterio- ing wounds on the affected pet, keep personal wounds sis, deep fungal infection, autoimmune skin disorders, canine covered and protected, do not allow the affected pet to lick pedal furunculosis, and neoplasia. the face or wounds of people, do not share the same bed as the affected pet, and do not share towels or linens with Diagnosis the affected pet. 3. Systemic antibiotics should be administered over the long 1. Rule out other differentials. term and continued 2 weeks beyond complete clinical 2. Cytology (impression smear, exudate): suppurative to pyo- resolution. The antibiotic should be selected on the basis granulomatous inflammation with bacterial cocci or rods. of in vitro sensitivity results because resistance is common 3. Dermatohistopathology: suppurative to pyogranuloma- (see Table 3-2). tous perifolliculitis, folliculitis, furunculosis, and nodular 4. Cleansing wipes (alcohol-free acne pads, baby wipes, to diffuse pyogranulomatous dermatitis. Intralesional bac- chlorhexidine-containing pledgets, or other antimicrobial teria may be difficult to find. wipes) used every 12 to 72 hours work very well. 4. Bacterial culture: primary pathogen is usually Staphylococ­ 5. For interdigital bullae, surgical removal of the ruptured cus. Mixed bacterial infections are also common. hair follicle and “ingrown” hair with a biopsy punch or laser speeds resolution. For developing bullae, topical Treatment and Prognosis dimethyl sulfoxide (DMSO) combined with enrofloxacin (to make a 10-mg/mL solution) and steroid (dexametha- 1. Any underlying cause should be identified and corrected sone to make a 0.1 mg/ml solution) should be applied (see Box 3-6). every 12 to 72 hours until lesions resolve. To prevent recur- 2. MRSP is a potential zoonosis, which is rapidly becoming rence, the feet should be wiped or scrubbed in the direc- a serious medical, ethical, and legal issue in veterinary tion of hair growth to remove any “ingrown” hairs. medicine. Infections appear to be rare in healthy people; 6. Adjunctive topical therapies that may be helpful include daily foot soaks for 10 to 15 minutes in 0.025% chlorhexi- dine solution, 0.4% povidone–iodine solution, or magne- sium sulfate (30 g/L water) for the first 5 to 7 days. BOX 3-6 Causes of Secondary Bacterial Alternatively, foot scrubs with antibacterial shampoo or Pododermatitis surgical scrub provided every 1 to 7 days as needed may be useful. Foreign body (e.g., plant awn, wood splinter, thorn) 7. Foot trauma should be minimized by having the dog con- Parasite (e.g., demodicosis, ticks, Pelodera, fined indoors, leash walked, and kept away from rough hookworm dermatitis) surfaces. Fungus 8. Fusion podoplasty, whereby all diseased tissue is removed Hypersensitivity (e.g., food, atopy) and digits are fused together, is a radical surgical alterna- Endocrinopathy (e.g., hypothyroidism, tive that is available for severe cases. hyperadrenocorticism) 9. The prognosis is good to guarded, depending on whether Trauma (e.g., stones, stubble, briars, wire floors, the underlying cause can be identified and corrected. In burns) severe and chronic cases, permanent fibrosis and scarring Autoimmune and immune-mediated skin disorders may contribute to future relapses by predisposing feet to traumatic injury. 72 CHAPTER 3 Bacterial Skin Diseases Bacterial Pododermatitis—cont’d AUTHOR’S NOTE Interdigital bullae are a common disorder of short- coated breeds. Active lesions should be removed and the patient treated for infection based on cytology and possible cultures. New bullae can be prevented with frequent wiping or scrubbing to the interdigital space in the direction of hair growth to remove and prevent “ingrown” hairs. Patients with interdigital bullae often have con- current chin pyoderma, which is likely caused by a similar mechanism. FIGURE 3-74 Bacterial Pododermatitis. Alopecia and crusting papular dermatitis that originated in the interdigital space progressing onto the dorsal surface of the foot. This bacterial infection occurred secondary to an underlying allergy. Note the lesion’s similarity to yeast dermatitis. FIGURE 3-72 Bacterial Pododermatitis. Severe swelling with alopecia, FIGURE 3-75 Bacterial Pododermatitis. This interdigital bulla (pedal ulcers, and draining lesions affecting only one foot. The infection had furunculosis) was apparent only when the toes were separated and the progressively worsened once over the previous several weeks. interdigital space examined. FIGURE 3-73 Bacterial Pododermatitis. Close-up of the dog in Figure FIGURE 3-76 Bacterial Pododermatitis. Interdigital erythema and 3-72. Profound tissue swelling and drainage with alopecia and crusting alopecia in an allergic dog. The bacterial infection is secondary to an ulcers are apparent. underlying allergy and subsequent foot licking that created a persistently moist environment.  Bacterial Pododermatitis 73 FIGURE 3-77 Bacterial Pododermatitis. Severe swelling with alopecia, erythema, and erosions. The infection occurred secondary to allergic dermatitis. FIGURE 3-78 Bacterial Pododermatitis. This chronic interdigital fistula and draining tract (pedal furunculosis) were caused by a penetrating plant foreign body. FIGURE 3-79 Bacterial Pododermatitis. Diffuse alopecia, erythema, and swelling affected most of the cutaneous surface. This severe case also had multiple erosions and draining lesions around the nail bed and in the interdigital space. 74 CHAPTER 3 Bacterial Skin Diseases Canine Pedal Furunculosis (Interdigital Bullae, Interdigital Pyogranuloma) Features 2. If draining lesions are secondarily infected, appropriate antibiotics or antifungal medications should be adminis- The etiopathogenesis is unclear, but one hypothesis is that tered for a minimum of 4 to 6 weeks. sterile pedal furunculosis is a persistent, immune-mediated, 3. For solitary lesions, surgical excision or laser ablation may inflammatory response to keratin and triglycerides liberated be curative. from ruptured hair follicles, sebaceous glands, and the pan- 4. Cleansing wipes (alcohol-free acne pads, baby wipes, niculus. The condition is thought to develop after the initiat- chlorhexidine-containing pledgets, or other antimicrobial ing case of furunculosis (e.g., mechanical, infectious, parasitic, wipes) used every 12 to 72 hours work very well. For inter- allergic) has been resolved. It is uncommon in dogs, with digital bullae, surgical removal of the ruptured hair follicle short-coated breeds possibly predisposed. and “ingrown” hair with a biopsy punch or laser speeds Canine pedal furunculosis manifests as single to multiple, resolution. For developing bullae, topical DMSO com- erythematous papules; firm to fluctuant nodules; or bullae of bined with enrofloxacin (to make a 10-mg/mL solution) one or more feet that appear in the interdigital areas. The and steroid (dexamethasone to make a 0.1 mg/ml solu- lesions may be painful or pruritic; may ulcerate; may develop tion) should be applied every 12 to 72 hours until lesions draining tracts with serosanguineous or purulent exudates; resolve. To prevent recurrence, the feet should be wiped or and, with chronicity, may become fibrotic. Lesions spontane- scrubbed in the direction of hair growth to remove any ously resolve, wax and wane, or persist indefinitely. Regional “ingrown” hairs. lymphadenopathy is common, but no systemic signs of ill­ 5. Alternatively, treatment with combination tetracycline and ness are noted. Secondary bacterial and yeast infections are niacinamide may be effective in some dogs. A beneficial common. response should be seen within 6 weeks of treatment ini- Interdigital bullae are a common problem in short-coated tiation. Administer 500 mg of each drug (dogs >10 kg) or breeds. Their severity and recurrence are often worsened by 250 mg of each drug (dogs ≤10 kg) PO every 8 hours until underlying pruritic disease such as atopy. Although the cause lesions have resolved (approximately 2–3 months) (see is unknown, short hairs that are forced through the follicle, Table 8-2). Then administer each drug every 12 hours for creating a sterile furuncle, which subsequently becomes sec- 4 to 6 weeks, subsequently attempting to decrease fre- ondarily infected, seem to be an important component of the quency to every 24 hours for maintenance. Anecdotal disease. “Ingrown” hairs are a key feature in the development reports suggest that doxycycline 10 mg/kg should be of interdigital bullae. administered every 12 hours until response occurs and then tapered to the lowest effective dose (doxycycline may Top Differentials be substituted for tetracycline). Differentials include bacterial pododermatitis, demodicosis, 6. Anecdotal reports suggest that treatment with cyclosporine dermatophytosis, deep bacterial and fungal infections (cellu- 5 mg/kg PO administered every 24 hours may be effective litis), autoimmune skin disorders, and neoplasia. in some dogs. When clinical resolution is achieved (usually within 6 weeks), cyclosporine should be gradually tapered Diagnosis to the lowest possible daily or alternate-day dose that maintains remission. Addition of ketoconazole (5–11 mg/ 1. Based on history, clinical findings; rule out other kg/day PO with food) to the regimen may allow for further differentials. reduction in the cyclosporine dosage. 2. Cytology (aspirate of nodule or nonruptured bulla): (pyo) 7. For severe, nonsurgical, or multiple lesions, treatment with granulomatous inflammation with no microorganisms glucocorticosteroids may be effective. Prednisone or pred- unless secondary infections are present. nisolone 2 to 4 mg/kg PO should be administered every 3. Dermatohistopathology: multifocal, nodular to diffuse, 24 hours. Significant improvement should be seen within (pyo)granulomatous dermatitis. Special stains do not 1 to 2 weeks. After lesions have resolved (≈2–3 weeks), the reveal infectious agents unless secondary infections are steroid dose should be gradually tapered to the lowest present. alternate-day dose that maintains remission. In some 4. Microbial cultures (biopsy specimens): negative for bacte- dogs, steroid therapy can eventually be discontinued. Sec- ria, mycobacteria, and fungi. ondary infections are common and should be treated aggressively. Treatment and Prognosis 8. The prognosis is good to fair. Lifelong medical therapy 1. The clinician should make sure that the initiating cause of may be needed to maintain remission, and interdigital the furunculosis (e.g., food allergy, wet environment, dirt fibrosis may be a permanent sequela in chronic cases. kennels, friction in short-coated breeds) has been identi- fied and corrected.  Canine Pedal Furunculosis 75 FIGURE 3-80 Pedal Furunculosis. The large, flaccid bulla in the FIGURE 3-81 Pedal Furunculosis. Severe interdigital tissue swelling interdigital space is typical of this disease. with ulceration was caused by traumatic furunculosis and subsequent recurrent bacterial infections. FIGURE 3-82 Pedal Furunculosis. Interdigital bulla with a moist FIGURE 3-83 Pedal Furunculosis. The toes have been separated, exudate and bruising of the surrounding tissue. revealing the interdigital space, which appears bruised. The skin seems thin, with a focal area of exudate identifying a focal abscess. FIGURE 3-84 Pedal Furunculosis. The clinician is applying gentle FIGURE 3-85 Pedal Furunculosis. Expressed material includes an pressure to the lateral aspects of the lesion to demonstrate the presence exudate with numerous hairs. These hairs act as a foreign body and a of hair within the abscess. This technique is not recommended because nidus for recurrent secondary infections. rupturing the lesion internally could worsen cellulitis and scarring. 76 CHAPTER 3 Bacterial Skin Diseases Canine Pedal Furunculosis—cont’d FIGURE 3-86 Pedal Furunculosis. A small interdigital bulla. FIGURE 3-87 Pedal Furunculosis. The interdigital tissue is affected by a severe pyogranulomatous infiltrate that results in cellulitis. FIGURE 3-88 Pedal Furunculosis. Severe swelling of the interdigital FIGURE 3-89 Pedal Furunculosis. A focal interdigital bulla that has space caused by chronic inflammation. ruptured and is draining a purulent exudate. FIGURE 3-90 Pedal Furunculosis. Severe interdigital cellulitis with a deep ulcerative tract.  Subcutaneous Abscess 77 Subcutaneous Abscess (Cat and Dog Fight or Bite Abscess) Features Disease occurs when normal oral bacterial microflorae are inoculated into the skin through puncture wounds. A history of a recent cat or dog fight can usually be documented. Sub- cutaneous abscesses are common in dogs and cats, especially among intact male cats. Subcutaneous abscesses are characterized by localized, often painful, swelling or abscess with a crusted-over puncture wound from which a purulent material may drain. Lesions are most commonly found on the tail base, shoulder, neck, face, or leg. Regional lymphadenomegaly is common. Animals may be febrile, anorexic, and depressed. Top Differentials FIGURE 3-91 Subcutaneous Abscess. Submandibular swelling in this Doberman was caused by an extensive subcutaneous abscess. (Courtesy Differentials include abscess caused by a foreign body, other of D. Angarano.) bacteria (e.g., actinomycosis, nocardiosis, mycobacteriosis), or neoplasia. Diagnosis 1. History, clinical findings. 2. Cytology (exudate): suppurative inflammation with a mixed bacterial population. 3. Polymerase chain reaction (PCR) analysis, when available, may simplify the diagnosis. Treatment and Prognosis 1. The abscess should be clipped, lanced, and cleaned with 0.025% chlorhexidine solution. FIGURE 3-92 Subcutaneous Abscess. Feline abscess caused by a cat 2. Systemic antibiotics should be administered for 7 to 10 bite. The syringe contains purulent material aspirated from the abscess. days or until lesions completely heal. Effective antibiotics include the following: Amoxicillin 20 mg/kg PO, SC, or IM q 8 to 12 hours (cats) Clavulanate–amoxicillin 22 mg/kg PO q 8 to 12 hours Clindamycin 10 mg/kg PO or IM q 12 hours Cefovecin sodium (Convenia) 8 mg/kg SC 3. The prognosis is good. Castrating intact male cats is a helpful preventive measure. FIGURE 3-93 Subcutaneous Abscess. Same cat as in Figure 3-92. The abscess has been lanced, and purulent material is easily expressed. 78 CHAPTER 3 Bacterial Skin Diseases Subcutaneous Abscess—cont'd FIGURE 3-94 Subcutaneous Abscess. Large subcutaneous swelling FIGURE 3-95 Subcutaneous Abscess. Same dog as in Figure 3-94. on the neck, typical of an abscess. The syringe contains fluid aspirated from the mass. Note that the serosanguineous fluid is more typical of a seroma. FIGURE 3-96 Subcutaneous Abscess. Purulent exudate covering a FIGURE 3-97 Subcutaneous Abscess. Purulent exudate being large ulcer on the dorsum of a cat. Necrotic skin covering the abscess has expressed from an abscess on the inguinal region of a cat. been debrided and is lying on the gauze pad. FIGURE 3-98 Subcutaneous Abscess. Large ulcer on the thorax of a FIGURE 3-99 Subcutaneous Abscess. The abundance of purulent cat covered with a purulent exudate. The overlying skin had necrosed exudate is typical of feline abscesses. and was removed.  Botryomycosis 79 Botryomycosis (Bacterial Pseudomycetoma, Cutaneous Bacterial Granuloma) Features Treatment and Prognosis Botryomycosis is an unusual type of skin infection in which 1. Nodules should be surgically excised; systemic antibiotics bacterial organisms form macroscopic or microscopic tissue should be administered over the long term (minimum 4 granules. Infection may be a sequela to a penetrating injury, weeks) based on in vitro sensitivity results. Without foreign body reaction, or bite wound. Botryomycosis is surgery, antibiotic therapy alone is rarely effective. uncommon in dogs and cats. 2. The prognosis is good with combined surgical and medical Botryomycosis appears as single to multiple nonpainful, therapy. and usually nonpruritic, firm nodules with draining fistulae. Purulent discharge may contain small, white granules (mac- roscopic colonies of bacteria). Lesions develop slowly and may appear anywhere on the body. Top Differentials Differentials include actinomycosis, nocardiosis, mycobacte- riosis, deep fungal infection, neoplasia, and foreign body reaction. Diagnosis 1. Cytology (exudate): suppurative inflammation that may contain granules composed of dense bacterial colonies. 2. Dermatohistopathology: nodular to diffuse (pyo)granulo- matous dermatitis and panniculitis with tissue granules composed of bacteria. 3. Bacterial culture: causative organism is usually Staphylococ­ cus, but occasionally other bacteria such as Pseudomonas FIGURE 3-101 Botryomycosis. The swelling of this cat’s foot was or Proteus are isolated. associated with moderate pain and lameness. The crust was covering a 4. PCR analysis, when available, may simplify the diagnosis. deep tract that periodically drained a purulent exudate. FIGURE 3-100 Botryomycosis. Deep draining lesion with superficial FIGURE 3-102 Botryomycosis. Tissue grain dissected from the foot of crust formation on the dorsum of a cat. the cat shown in Figure 3-101. 80 CHAPTE