Diagnostic Hallmarks
Distribution: finger webs, elbows, axillary folds, buttocks, breasts, and penis
History of contagion (family members or sexual partner with evidence of similar disease)
Identification of the mites, feces, or ova in scrapings from lesions
Response to therapy
Clinical Presentation
Scabies is basically a vesicular disease but the intensity of itching leads to such vigorous scratching that vesicles are destroyed as quickly as they are formed. This results in a presentation that almost always appears predominantly eczematous in morphology. Careful examination in a suspected case usually does reveal an occasional intact oval or linear vesicle (burrow), but these are terribly easy to overlook. The width of scabetic burrows is about 1 mm, and the length is generally 1.5 to 3.0 mm. Inflarnmation is prominent in excoriated lesions but is variable around intact burrows.
The distribution of lesions is quite characteristic. Burrows and excoriated papules are most commonly found in the web spaces of the fingers, around the elbows, on the anterior axillary folds, and over the buttocks. The breasts in women and the shaft and glans of the penis in men are also frequently affected. In patients with chronic infestation, widespread involvement of the trunk and extremities may also be noted. The face, except occasionally in infants, is normally spared.
Initially, burrows and eczematous papules are few in number, isolated, and widely separated. The scattered nature and small size of the eczematous lesions is a valuable diagnostic clue during the first few weeks of infestation, but this feature is lost in well-established cases of many months duration.
A history of contagion is an important diagnostic feature. Therefore, patients should be queried about the presence of pruritic eruptions in family members, friends, and sexual partners. In instances where clinical suspicion is high, it is permissible to attempt confirmation of one's diagnosis through a therapeutic trial of antiscabetic medication. Rapid response, as measured by abrupt cessation of itching, is tantamount to proof of diagnosis.
Identification of the mite in scrapings from lesions is theoretically desirable but is not always possible. In fact, scrapings carried out from any lesion other than an intact burrow are so rarely positive they are not worth the effort. When an intact burrow is present, the roof can be lifted off with a thin scalpel shave technique. This roof, together with material subsequently scraped from the base of the burrow, is then transferred to a microscope slide. A drop of immersion oil is placed over the scrapings, and a coverslip is applied. Examination under low power will regularly reveal mites, ova, or feces.
Atypical Manifestations. In a small number of patients a residuum of long-lasting, dome-shaped, erythematous, pruritic nodules remains after treatment has been completed. These papules and nodules are most commonly seen in young men, particularly around the waist and in the groin. These lesions do not contain live mites, instead, they apparently form as an immunologic response to scabetic antigenic material that remains after treatment. The lesions do eventually disappear but their resolution can be hastened by the intralesional injection of triamcinolone.
Under some circumstances (very poor hygiene, marked immunosuppression, or in institutionalized persons), scabetic infestation can become overwhelming, so that the entire body is involved in a generalized eczematous eruption. Such widespread infestation, sometimes severe enough to be termed exfoliative erythrodermatitis, has in the past been known as Norwegian scabies.