Dermatology Lecture 9: Parasitic Skin Diseases 2022-2023

# Dermatology ## Lecture 9: Parasitic Skin Diseases ### 2022-2023 ## Parasitic Skin Diseases ### Scabies - Scabies is a contagious disease caused by a mite, the female *Sarcoptes scabiei*, which invade the epidermis and form a burrow. - **Direct:** Close personal contact with infected patient (...

# Dermatology ## Lecture 9: Parasitic Skin Diseases ### 2022-2023 ## Parasitic Skin Diseases ### Scabies - Scabies is a contagious disease caused by a mite, the female *Sarcoptes scabiei*, which invade the epidermis and form a burrow. - **Direct:** Close personal contact with infected patient (sexual or nonsexual). - **Indirect:** Infection through fomites as towels, cloths, or beds (especially in severe and/or crusted cases). - **Incubation Period:** 2 weeks – 2 months. - The **pathognomonic lesions** of scabies are the burrows which may be present in a few or large numbers. - The **lesion:** - At the end of the burrow a vesicle or papule is usually seen. - Burrows are seen early in infection. - Later on, repeated itching removes the roof of the burrows, and it may be difficult to find any. - **Severe itching** is worse at night. - **Allergic sensitivity** to the mite or its products is the cause of itching & development of lesions other than burrows. - **Other lesions that are seen in scabies include:** - Small urticarial papules, scratch marks. - Eczematous plaques which is prominent on the breast of women. - Secondary infection as pustules, boils, and impetigo. - Vesicles may occur independently of burrows especially at the sides of fingers. - Bullae may be seen in infants particularly on palms & soles. - **Distribution** of lesions is very characteristic, usually the delicate parts of the skin. - **Usually generalized & symmetrical.** - **The sites affected are:** - The finger webs, anterior aspects of the wrists - Ulnar border of hand & forearms - Elbows, axillae - Around the nipples in women - Abdomen, periumbilical region - Male genitalia, natal cleft, lower parts of buttocks - Medial aspects of thighs, legs, around ankles & dorsa of feet. - **Face & interscapular region are usually free.** ### Clinical Types - **Human classic scabies** described above. - **Animal scabies** - The differences from human scabies are: - **Shorter I.P.** - **Self-limiting** after eliminating the source of infection. - **Sites:** localized or generalized according to the mode of exposure. - Webs & genitalia are free. - **Lesions:** papules, wheals or papulovesicles with **absence of burrows**. - It is **not transmitted** from human to human. - **Scabies in infants and young children** - Has **atypical distribution of lesions** with involvement of scalp, face, neck, palms and soles. - **Nodular scabies** - Persistent reddish brown pruritic nodules may occur after treatment of scabies. - The sites of predilection are axillae, male genitalia, groins, umbilicus or anywhere. - These nodules represent **hypersensitivity** reaction to mites. - **Scabies incognito** - The lesions and the course are modified by the application of topical or systemic steroids. - Scabies has **unusual extent and distribution**. - This type represents an abnormal host immune response to the mite. - The condition is seen in the following groups. - Mentally retarded. - Patients with poor cutaneous sensation - Patients with severe systemic diseases like leukemia and DM. - **Crusted (Norwegian) scabies** - Clinically Norwegian scabies is characterized by: - Large crusts on the hands and feet with subungual hyperkeratosis. - Erythematous scaly plaques occur on the face, neck, scalp and trunk and may become generalized. - Itching may be absent - The number of the invading mites may reach up to 2 millions, so these patients are **highly contagious** and may initiate epidemics of scabies. ### Complications - **Bacterial infections**, e.g., impetigo, cellulitis, lymphangitis, boils and folliculitis. - **Eczema** may follow scratching or application of topical scabicides. - **Acarophobia**: - After successful treatment - The patient continues to itch and believes that he still has scabies - Such patient usually has **psychological disorder**. ### Diagnostic Criteria - **Marked itching** worse by night. - Infection of **more than one member of the family**. - **Classical distribution**. - **Polymorphic eruption**. - **Demonstration of the mite under microscope**: - Burrow is moistened with KOH 20% and scraped with a blunt scalpel. - The scraping is examined under microscope for mites, eggs and/or fecal pellets. - Dermoscopy can prove useful for **direct *in vivo* visualization** of mites and eggs. ### Differential Diagnosis - Popular urticaria - Eczema - Erythema multiform ## Treatment ### General Measures - Boiling of cloths, bed linens, towels. - The mites cannot survive at temperature about 50°C for longer than 5 min. - It cannot survive at room temperature in blanket or clothing for more than 2w - Treatment of all members of the family except in animal scabies. - Treatment of infested animals. - Are applied to the entire trunk and extremities. ### Topical Scabicides | Drug | Application | Pros & Cons | |---|---|---| | Permethrin 5% (the treatment of choice) | Applied for 2 successive nights, then washed 24 hours after the second application, a third application after 8 d | Pros: It is safe in infants and pregnant women | | Crotamiton 10% | Applied for 2 successive nights, then washed 24 hours after the second application. | | | Benzyl benzoate 25% | For 2 successive nights. | | | Sulfur: 10% in adults, 3-5% in infants and children | It is applied every night for 4 successive nights. | Pros: However, it is safe in infants, children, and pregnant women. Cons: It is less acceptable because of odour, messiness, staining | | Gamma benzene hexachloride 1% | One application is left for 12 hours. | Cons: Not used in infants, young children, pregnant or lactating women and in patient with seizures | | Malathion 0.5% | Applied for 12 h then washed. | | | Ivermectin 1% solution | Applied for 12 hours then washed with a second application after a week. | | ### Systemic Scabicides - **Oral Ivermectin:** - Very effective antiscabetic drug. - 6 mg tablets. - Dose: 6 mg/15 kg single dose (0.2-0.4 mg/kg); repeated after one or 2 weeks. - It is extremely safe, but is not recommended for children who weigh <15kg, pregnant women and breastfeeding mothers - **Antihistamine for itching.** - **Antibiotic for bacterial infections.** ### Treatment of Nodular Scabies - Intralesional injection of steroid - Surgical excision. ### Causes of Persistent Itching After Treatment of Scabies - Persistence of hypersensitivity state which will spontaneously subside - Unsuccessful treatment - Irritation of the skin by the antiscabetic topical drugs. - Nodular scabies. - Acarophobia. - Reinfection. ## Pediculosis - **Pediculosis** is caused by **lice**, which are small gray-brown, blood sucking parasites - Each female lays many **eggs**, which appear as **nits**, firmly attached (cemented) to the hair shaft - Each nit hatches within a week. ### Pediculosis Capitis (Head Lice) - **Site:** Pediculosis Capitis occurs on the hair of the scalp, mainly above the ears and occiput. - **MOI:** Pediculosis capitis is communicated by direct contact, sharing hats, combs & brushes. - **Epidemiology:** Although the disease is more common in children, it may occur in adults. - **Clinical picture:** There is **itching** of the scalp, this causes scratching with **impetigo** and cervical lymphadenopathy. - **Association:** The general health may be impaired from septic absorption. ### Treatment of Pediculosis Capitis - **Cutting the hair short and systemic antibiotic if there is impetigo.** - Co-trimoxazole is the preferred antibacterial because it also has pediculicide effect. - **Pediculicides are given after control of bacterial infection.** - **Topical pediculicide lotion**: Malathion 0.5%, Ivermectin 1%, or Permethrin 5%. - It is applied to the dry clean hair for 12 hours then washed. - Any medication must be repeated after one week (to kill the residual nits and to overcome resistance). - **Oral Ivermectin**: 0.2-0.4 mg/kg single dose that must be repeated after 8 d. - **Removal of nits**: - Is done by application of white vinegar diluted with equal amount of water. - Vinegar will dissolve the cement substance that attaches the nits to the hair shaft. - Washing is done after 1 - 2 hours and comb the hair with fine-toothed comb to remove the nits. ### Pediculosis Pubis (Crab Lice, Pthirus Pubis) - **Def:** The pubic louse is **sexually transmitted** and is mostly found in young adults. - Pubic lice infest the pubic and perineal hair - It may also infect the eye lashes - **Site:** - **Lesion:** Crab lice cause severe itching in the pubic region with 2ry eczema and infection. - The lice firmly adhere to the base of hairs - They can be skin-coloured or mimic **haemorrhagic crusts**. ## Urticaria - Urticaria is an acute skin disorder characterized by formation of **wheals**. - It may be allergic or non-allergic. - Liberation of histamine and or other substances from the mast cells may result - from Allergic Reaction nearby the mast cells - from Non-Allergic Reaction, i.e., direct action of certain stimuli on mast cells. ### Causes - Foods (fish, egg, strawberries) - Food additives (e.g., yellow azo dye and benzoate) - Drugs e.g., Aspirin, morphine, sulpha, penicillin, blood and blood products. - Infections: e.g. - Bacterial: tonsillitis, sinusitis, cystitis, prostatitis, cholecystitis, dental abscess. - Viral: hepatitis B. - Fungal: dermatophytosis, candidiasis. - Parasitic: ascaris. - Protozoal: trichomonas. - Inhalants: dust, pollen, perfumes, feather, tobacco. - Collagen diseases e.g., SLE, dermatomyositis and rheumatoid arthritis. - Neoplasms: lymphoma, leukaemia & internal malignancy. - General diseases: thyrotoxicosis, uraemia, liver diseases, polycythaemia vera. - Physical factors: sun, cold, water, heat. - Psychogenic causes: emotional stress, anxiety. - Unknown: 50% of acute urticaria are idiopathic and about 90% of chronic urticaria are either idiopathic or autoimmune due to histamine releasing autoantibodies. ### Clinical Picture - **Common skin disease characterized by sudden appearance of itchy wheals** that last from few hours up to 48 hours, then fade away (evanescent) and new lesions may appear, a feature distinguishing urticaria from other urticarial like lesions of the skin. - The wheals appear as erythematous papules, plaques and or streaks. - The lesions may be localized or generalized. - The size is variable from pinpoint to many inches across. - The shape of the lesion may be bizarre, geographic & or annular. - **Association:** - **Angioedema** (diffuse swelling in certain areas of thin skin & loose SC tissue such as eye lids, lips, genitalia) may occur with wheals. - **General symptoms** may indicate involvement of internal organs such as - GIT (nausea, vomiting, dysphagia) - respiratory tract (hoarseness, wheezing and dyspnea). ### Course - **Acute urticaria:** the lesions usually disappear within a few hours or days - **Chronic urticaria:** the disease persists for more than 6 weeks - **Spontaneous improvement** may occur even in absence of diagnosis or treatment. ### Special Types of Urticaria - Angioedema - Dermographism - Cold urticaria - Aquagenic urticaria - Cholinergic - Solar urticaria - Contact urticaria - Serum sickness ### Treatment - Careful search for the cause and its removal if possible is essential. - Antihistamines: specific treatment - Systemic steroids: adjuvant treatment in severe cases resistant to other treatments. - Adrenaline - Ca gluconate - Local soothing lotion, as calamine lotion ## Papular Urticaria (Prurigo Simplex) - **Def:** Hypersensitivity to insect bites such as fleas and mosquitoes. - **Clinical picture:** - Occurs in infants and children. - **Lesions**: - itchy small red papules 1-5mm. - arise on top of wheals or independently on normal skin. - Vesicles are also rarely seen. - Due to itching the papule becomes excoriated and secondary infection may occur. - **Sites:** - The eruption occurs mainly on the limbs. - The trunk may show few lesions. - **Course:** It is frequently seen in children moving to new areas where mosquitoes prevail. - **Resolution:** It usually subsides spontaneously, even when exposure to mosquitoes continues. This probably results from a process of gradual desensitization to the antigens of mosquitoes. - **Maybe:** Prurigo of Herba (atopic) - It may persist indefinitely with remission & exacerbation in atopic individuals in whom the lesions are numerous & the skin is lichenified. - Superficial lymphadenopathy especially of the inguinal and axillary glands is usually present. - The association of - itching, lichenified skin, - excoriated shotty papules - superficial lymphadenopathy - is known as prurigo of Hebra. ## Atopic Dermatitis - **If 4 major criteria:** - Pruritis - Typical morphology and distribution for age group - Chronic or chronically relapsing dermatitis - Personal or family history of atopy ### Treatment - **General:** - Disinfestations. - Change of environment - **Drugs:** - Oral antihistamines. - Short course of systemic steroids in extensive cases. - Local soothing lotion or topical steroids. ## Case Scenario > A 31 y-old man is complaining of itching that is worse by night of 3 weeks duration. 2 days ago his wife also started to scratch her skin especially during sleep. > **Q1 - What are the classic sites you must examine to search for skin lesions?** > **Q2 - Enumerate the types of lesions you expect to find.** > **Q3 - What is the most probable diagnosis?** ### Answers - **Q1:** The webs of fingers, flexure aspects of wrist joints, antecubital fossae, axillae, around the umbilicus, groins, buttocks, medial aspects of thighs and dorsae of feets. - **Q2:** Polymorphic eruption: papules, scratch marks, excoriated papules, impetigo lesions (superficial bacterial infection) in the form of pustules and crusted lesions. - **Q3:** Diagnosis is scabies. ## Questions 58 - **1 - Scabies in infancy can be treated by:** - a) Permethrin 2.5-5%. - **2 - Primary lesion of scabies is** - b) Burrow. - **3 - Papular urticaria is caused by:** - d) Insect bites **Ans: 1-a, 2-b, 3-d**