Scabies
An eruption caused by a mite, Sarcoptes scabiei. The female mite burrows into the skin and deposits eggs, which hatch into larvae in a few days. Scabies is easily transmitted by skin-to-skin contact and can be rapidly spread between residents of the same household, nursing home, or institution. Infestation is usually present for weeks before the patient becomes allergically sensitized to the insects and develops itching.
Symptoms and signs: Eventually the patient experiences intense pruritus, which usually worsens at night. On examination, the skin is usually excoriated. The characteristic sign is the burrow—a linear ridge with a vesicle at one end—where the mite is usually found. Burrows are common in the interdigital webs, the flexor aspects of the wrists, the axillae, the umbilicus, around the nipples, and on the genitalia. Erythematous papules or nodules in the same areas are also common.
In the elderly, scabies may present less typically, especially if untreated for a long time. The condition may mimic eczema or exfoliative dermatitis because widespread thick crusted lesions are present. The patient may have erythroderma and generalized lymphadenopathy.
Diagnosis and treatment: A mite at the end of a burrow can sometimes be excavated with a needle or a scalpel blade, placed in a drop of mineral oil, and detected under a microscope. However, even in long-term cases with widespread excoriations, few mites are present, and they may be impossible to find. Therefore, treatment is usually based on a
presumptive diagnosis.
A lotion or cream containing lindane 1% should be applied to the entire body from the neck down. All patients need help applying the medication and must understand that all areas must be covered. After 24 h, the patient should bathe; all clothes and bed linens should be machine-laundered in hot water or dry-cleaned.
A second application of the cream or lotion, also left on the body for 24 h, should be made 7 days later to kill any newly hatched larvae. Itching, which results from allergic sensitization and not from viable organisms, may not subside until 1 to 2 wk after treatment. However, itching can be effectively treated with topical corticosteroids or, in severe cases, with a tapering course of oral corticosteroids.
All household members and close personal contacts should also be treated. In a nursing home, all clinical staff, patients, and their household contacts should be treated on the assumption that some infested persons are still asymptomatic.