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Human scabies, caused by the Sarcoptes scabiei mite, is one of the most common contagious dermatoses. In HIV patients, this organism can cause “crusted scabies,” also known as Norwegian scabies, which denotes an overwhelming scabies infestation. In typical scabies, the mites cause extremely pruritic burrows, vesicles, and papules in a characteristic distribution involving the finger webs, sides of the hands and feet, breasts, waist, and groin. Pruritus is most intense at night. In contrast, crusted scabies typically affects the hands and the feet with asymptomatic crusting and does not cause significant pruritus. Transmission through infected linens or clothing is common in cases of Norwegian scabies. Risk factors include poor hygiene, crowding, and exposure to pets.
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Most often the diagnosis of scabies is made clinically, with evidence of burrows and severe pruritus in a characteristic distribution. Definitive diagnosis is made from examination of shavings from the lesions. Placing mineral oil over a suspected lesion and then shaving it with a number 15 blade can demonstrate the mites, which are usually 0.3 to 0.4 mm in length.
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Management and Disposition
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Topical permethrin 5% cream has a low toxicity and is the treatment of choice for scabies. Patients are instructed to apply the cream from the neck down and leave it on for 8 to 14 hours before removal. One application is usually sufficient for treatment in nonimmunocompromised patients, but a 2nd application may be needed for severe disease. The patient’s clothes and bedding should be washed in hot water. Antihistamines should be prescribed to alleviate the pruritus. Often the pruritus persists after treatment as a hypersensitivity reaction to the mites and their feces and eggs. Any complicating secondary skin infection should be treated with appropriate systemic antibiotics. Localized infections can be treated with topical steroids.
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For HIV patients with Norwegian scabies, permethrin should be applied to the face, scalp, behind the ears, and from the neck downward. Repeat treatments may be needed. For severe or refractory cases, oral ivermectin (200 mg/kg for one dose) can be tried with the exception of pregnant or lactating women.
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Often secondary staphylococcal infections complicate the diagnosis, including impetigo, ecthyma, paronychia, and furunculosis.
Oral antibiotics are often indicated for Norwegian scabies because of skin breakdown and secondary infections.
Close contacts of infected patients should be treated simultaneously. Inform patients that although the scabicide will kill the mites, itching may last for weeks. Patients often seek repeat treatments and inappropriately receive additional scabicides, which can cause contact dermatitis.
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