Scabies

Scabies is an excruciatingly pruritic skin infection produced by the mite, Sarcoptes scabiei. The mite is transmitted by close contact with an infected person, and infects the stratum corneum of the skin. The itching occurs after a week or two, as a result of the host immune response to the presence of the mite. Therefore, not all infected people may be symptomatic initially.

In addition to the intense itching, which is often the worst at night, patients present primarily with signs consistent with scratching. Redness, excoriations, and scale are usual. The classic specific lesion of scabies is the burrow, a 1 to 3 mm red, edematous linear papule or vesicle, most often located in the finger and toe web spaces, the ventral wrists, and on inframammary skin. However, in the axilla and on anogenital skin (most often, however, on the scrotum and penis) very itchy, red, excoriated, dermal nodules are characteristic (Fig. 22).

The differential diagnosis includes other very itchy skin diseases including lichen simplex chronicus (eczema/atopic dermatitis) and irritant/allergic contact dermatitis. The more discreet and specific nodules can be confused with folliculitis, furunculosis, and hidradenitis suppurativa, although scabetic nodules never drain.

The diagnosis is made by the history of intense pruritus, morphology, and distribution, and it is confirmed by demonstration of the organism (Fig. 23). A deep scraping/shave of a burrow often but certainly not always yields the microscopic identification of a mite, ova, or scybala (feces). Scraping a scabetic nodule of the ano-genital skin is not useful. However, a punch biopsy is characteristic of an insect bite.

The treatment of scabies includes elimination of the mite, control of the inflammatory response, and avoidance of reinfection by treating other family members and

Table 18 Trichomoniasis

Diagnosis

Symptoms Clinical appearance

Differential diagnosis

Therapy

Trichomo- Intense pruritus Introital, vaginal, and Vaginal candi- Oral metro-

and burning, irritation cervical erythema, ''strawberry'' cervix, purulent vaginal secretions that microscopically show white blood cells and trichomonads diasis, atrophic vaginitis, bacterial vaginitis, bacterial vaginosis, desquamative inflammatory vaginitis nidazole 500 mg b.i.d. for l wk or 2 g once

Scabies The Vulva

Figure 22 The pink papules with scale/crust are typical for scabies in skin folds and on the wrists.

fomites. The mite itself is treated with permethrin 5% applied overnight, and a second treatment one week later is often used but not generally needed. Lindane is no longer used for scabies due to concerns of neurotoxicity and local irritation, most common in infants (62,63). Alternatively, oral ivermectin is elegant and safe although not FDA approved (64). Scabies can be more difficult to eradicate in immunosuppressed patients, and the combination of topical and oral therapy is often necessary. Unfortunately, resistance to ivermectin has now been reported (65).

Scabies Feces
Figure 23 Identification of the mite, Sarcoptes scabiei, its feces, or ova proves the diagnosis of a scabies infestation.

Vulvovaginal Infections Table 19 Scabies

Differential

Diagnosis Symptoms Clinical appearance diagnosis

Therapy

Scabies Intense Excoriations, Eczema/lichen pruritus burrows, inflamed simplex

5% permethrin cream overnight or ivermectin orally dermal nodules chronicus, folliculitis, candidiasis

The short-term application of an ultrapotent topical corticosteroid such as clobetasol dipropionate ointment may help control itching. However, the thickened nature of scabetic nodules in the genital area precludes good penetration, and a few drops of triamcinolone acetonide 10mg/cc often produce rapid symptomatic improvement. Finally, all clothing and linens used within 48 hours should be either washed with hot soapy water or bagged for several days to eliminate the mite. All those living in the same home or in close contact should be treated with permethrin or ivermectin. Persistence of disease is frequently reinfection rather than resistance (Table 19).

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