Veterinary Dermatology Quiz

Approach to Crust, Scale, Environmental and Endocrine Dermatosis

• Various presentations of crust and scale are discussed.
• Crusts are composed of cells and dried exudate, potentially serous, sanguineous or purulent.
• Scales are accumulations of horny layer (cornified cells) fragments. Normal loss is of individual cells, but abnormal scaling involves larger flakes.
• Primary skin scaling disorders include Ichthyosis, and primary seborrhea which are generally not itchy. Secondary conditions account for over 80% of scaling disorders and are typically itchy.

Hereditary Skin Disorders

• Ichthyosis is an abnormal cornification.
• Nasal hyperkeratosis is also covered.
• Lamellar ichthyosis is discussed specifically in golden retrievers.

Secondary Causes of Crusting and Scaly Conditions

• Pruritic (itchy) causes: Parasites (scabies, Demodex, Cheyletiella); allergies (food, environmental); pyoderma (bacterial infections like Staphylococcus spp.).
• Non-pruritic/variably pruritic causes: Fungal infections (dermatophytosis), leishmaniasis, sebaceous adenitis, sterile pustular diseases; zinc-responsive dermatosis; lethal acrodermatitis, metabolic disorders (hypothyroidism), erythema multiforme; drug reactions, and neoplasia.

Clinical Approach to Diagnosis

• Diagnoses depend on the specific condition.
• Diagnostic tests include cytology (skin scraping), cultures (bacterial/fungal), biopsies, allergy testing, and blood tests (if systemic disease suspected). Diet changes may be necessary

Parasitic Conditions (Pruritic)

• Sarcoptes scabei: (mites) is highly pruritic, leading to papules, pustules, and crust formation in dogs and cats. The condition is frequently transmitted among animals (zoonotic) and even more commonly seen in foxes.
• Cheyletiella: Species-specific mites affecting cats, rabbits, and dogs; characterized by clinical signs of walking dandruff.
• Psoroptes cuniculi: Affects rabbits, irritating the ear lining and causing serum and thick brown crusts.

Pruritic Causes

• Allergic conditions; characterized by thickened lesions and scale formation.
• Pyoderma: Pus-filled bumps (pustules) lead to scaling and crusting from epidermal collarets.

Fungal Conditions (Non-pruritic)

• Dermatophytosis (fungal skin infection): Commonly seen in cats and dogs, often exhibiting circular scaling patches. Can involve the head, ears, and other areas.

Protozoal Conditions (Non-pruritic)

• Leishmaniasis: A zoonotic protozoal infection, uncommon in the UK, mainly found in imported rescue dogs, often associated with sandflies.

Sebaceous Adenitis

• Immune-mediated condition affecting the sebaceous glands. Common in certain breeds like standard poodles, Akitas, and Samoyeds, often appearing as dry skin scaling and alopecia.

Pemphigus Foliaceous

• Immune-mediated, leading to pustular diseases and scaling/crusting lesions.

Zinc-Responsive Dermatosis

• Type 1—Inability to absorb zinc from the intestines; typically affects Alaskan Malamutes and Siberian Huskies.
• Type 2—Diet deficient in zinc; often affecting Great Danes.

Metabolic Disorders

• Hepatocutaneous syndrome—Older animals, frequently characterized by scaly, crusty lesions, and thickened/fissured footpads.
• Hypothyroidism—Facial alopecia and scaling.
• Diabetes—truncal hypotrichosis with seborrhea, and sometimes dull coat

Erythema Multiforme

• Hypersensitivity reaction to infections, or drugs.
• Lesion patterns might be in annular/polycyclic shapes.

Drug reactions

• Results of taking drugs.
• Usually occurs within two weeks of administrating.
• Causes numerous reactions and crust/scale lesions.

Neoplasia (Epitheliotropic Lymphoma)

• Condition often seen in older dogs.
• Signs include scaly disease, and itching (pruritic).
• Definitive diagnosis relies on FNA/impression smears and biopsies.
• Treatment often involves chemotherapy and steroids.

Environmental Dermatoses

• Solar dermatitis—Chronic skin damage from UV radiation exposure. Photo-sensitization is also discussed here as a condition where skin becomes more susceptible to UV light due to photodynamic agents, often with poorly pigmented nasal skin in dogs.
• Tick infestation/Myiasis—More common in warmer climates.
• Foreign bodies— Common in dogs; leads to pododermatitis and ear infections; often involving migrating grass seeds, surgical inspection and flushing are required.
• Contact dermatitis- Often caused by environmental allergens including plants, gardening supplies, some chemicals, plastics, metals, abrasives, soaps, and other household cleaners for instance.
• Burns—Common from thermal or chemical injury, diagnosing by history and thorough physical examinations.
• Frostbite—Cold temperature injury, diagnosis by history and a complete physical exam are needed.
• Intertrigo—Skin fold dermatitis is typical and is especially common in dogs such as bulldogs and Shar-Peis. Poor air circulation in skin folds can cause increased bacterial or Malassezia overgrowth in the skin fold areas.

Endocrine Dermatoses

• Hypothyroidism—An often overlooked diagnosis, typically seen in middle-aged dogs of medium to large breeds and also characterized by symptoms of low thyroid function including lethargy, mental dullness, bradycardia, weight gain, hypothermia, myxedema, otitis externa, reduced fertility, neurological signs (laryngeal paralysis, megaesophagus), and skin lesions. Diagnosing is made using clinical signs, compatible signalment characteristics, physical examination findings and clinico-pathological abnormalities. Also supported by specific endocrine tests. Treatment involves consistent levothyroxine 20-40 µg/kg daily dosage.
• Hyperadrenocorticism—A common endocrinopathy in dogs; characterized by excessive ACTH secretion which leads to adrenal hyperplasia, clinically significant signs often include polyphagia, weight gain, abdominal distension, muscle weakness, myotonia, skin atrophy (testicular), and neurological issues. Diagnosis is based on thorough clinical exam, patient history and results of various imaging and laboratory tests. Common treatment is lifelong use of trilostane for pituitary dependent HAC. Adrenal-dependent HAC is often treated surgically.

Alopecia X and Seasonal Flank Alopecia

• Alopecia X: a non-well understood condition. Alopecia is a loss in hair, while X is an abbreviated form of unknown, such as X-linked recessive disorder. Typically seen in Nordic breeds with plush coats, it is characterized by symmertical non-inflammatory alopecia with the loss of primary hairs, followed by secondary hair.
• Seasonal flank alopecia is a condition seen in certain breeds, like Airedales, Boxers, and Bulldogs, exhibiting hair loss specifically in the flank region during the seasonal changes.

Diagnostic Approaches

Various procedures are followed, relying on patient history, clinical presentation and physical exam findings, and diagnostic testing results to arrive at a diagnosis for cases characterized by crust, scale, environmental, or endocrine dermatosis.