Review Question - QID 107666

The patient’s clinical presentation and skin biopsy findings are consistent with scabies. The most appropriate treatment is with permethrin cream.

Scabies is a highly contagious skin infestation caused by the Sarcoptes scabiei mite. It is characterized by extremely pruritic, erythematous papules that tend to be distributed on the scalp, face, palms and soles in children or axillary folds, waist, genitalia, and extensor elbows and knees in adults. The presence of thin reddish-brown lines known as burrows, is pathognomonic, but may not always be present and can be obscured by excoriations or superimposed bacterial infections. Patients should be instructed to wash their clothes and linens. First line treatment is topical permethrin cream.

The diagnosis of scabies is supported by presence of burrows in the interdigital spaces and confirmed by the presence of mites on skin biopsy. Additionally, chronic immunosuppression, as in this patient with lupus on steroids, is known to predispose to outbreaks of scabies. Other predisposing factors include summer weather and crowded living conditions (such as skilled nursing facilities, schools, or prisons). The differential for diffuse, itchy rashes also includes contact dermatitis, tinea corporis, tinea versicolor, and cutaneous Candidiasis, none of which are associated with burrows. Contact dermatitis tends to present in a focal, linear pattern whereas tinea corporis, tinea versicolor, and Candida tend to be more confluent.

Figure A shows a skin biopsy with multiple scabies mites and ova.

Incorrect Answers:
Answer 1: Hydrocortisone cream is used for eczema, dermatitis, and hemorrhoids. Eczema or atopic dermatitis is marked by presence of flaky, dry skin and can be associated with other atopy such as allergies and asthma.
Answer 2: Nystatin cream is used for skin infection with Candida, also known as diaper dermatitis. It classically presents as "beefy red" plaques with "satellite" lesions.
Answer 4: Ketoconazole cream is used for the treatment of tinea corporis and tinea versicolor. Tinea corporis or ringworm is marked by presence of annular plaques whereas tinea versicolor tends to be hypo or hyperpigmented patches that are most noticeably after prolonged sun exposure.
Answer 5: Capsaicin cream is used for muscle and joint aches as well as neuropathic pain. It generally is not used in the treatment of skin rashes.

Scabies is a common health problem. Children, elderly, and immunocompromised patients are predisposed to getting infected and having higher mite counts. Many diagnoses are made clinically, but skin microscopy can be helpful in identifying the mites. Topical permethrin is a well known, beneficial treatment of scabies. Other alternative regimens include oral ivermectin and topical crotamiton, but these may be less effective than permethrin (1).