Sauer notes

1. Scabies should be ruled out in any generalized excoriated eruption.

2. The patient should always be asked if other members of the household itch.

PRIMARY LESIONS. A burrow caused by the female of the mite Sarcoptes scabiei (Fig 21-2) measures approximately 2 mm in length and can be hidden by the secondary eruption. Small vesicles may overlie the burrows. Scabies incognito is a form of the disease in which the burrows are not easily identified. Norwegian, or keratotic, scabies occurs in immunosuppressed patients. Hundreds of organisms create a psoriasiform dermatitis.

SECONDARY LESIONS. Excoriations of the burrows may be the only visible pathologic process. In severe, chronic cases, bacterial infection may be extensive and may take the form of impetigo, cellulitis, or furunculosis.

Residual nodular lesions may persist as an allergic reaction for many weeks or months after the organism is eliminated. They are often recalcitrant to therapy and topical, intralesional, and even systemic corticosteroids may be necessary. Nodular scabies is not contagious.

DISTRIBUTION. Most commonly the excoria-tions are seen on the lower abdomen and the back, with extension to the pubic and the axillary areas, the legs (ankles especially), the arms (flexor wrists especially), and the webs of the fingers.

SUBJECTIVE COMPLAINTS. Itching is intense, particularly at night, when the patient is warm and in bed and the mite is more active. However, many skin diseases itch worse at night, presumably due to a lower itch threshold when relaxation occurs.

COURSE. The mite can persist for months and years ("7-year itch") in untreated persons.

CONTAGIOUSNESS. Other members of the household or intimate contacts may or may not have the disease, depending on exposure and the severity of the infestation.

LABORATORY FINDINGS. The female scabies mite, ova, and fecal pellets may be seen in curetted burrows examined under the low-power magnification of the microscope (see Fig 21-2). Potassium hydroxide (20% solution) can be used to clear the tissue, as with fungus smears. Another method of collection is to scrape the burrow through immersion oil and then transfer the scrapings to the microscopic slides. Skill is necessary to uncover the mite by curetting or scraping.

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