Macrodistribution: Primary lesions in adults are found on the finger webs, finger margins, flexor surface of the wrists, elbows, axillary folds, ankles, and insteps. Adult men show a predilection for burrows on the genitalia. Adult women favor burrows on the palms and areolae of the breasts. Infants often show tracks on the palms, soles, and scalp (see Figs. 11-13).
Indicated Supporting Diagnostic Data
The definitive lab test for scabies is an ectoparasite examination. This is performed by identifying and scraping the distal vesicular end of one or several burrows, smearing the material on a microscope slide, and examining the specimen after adding a drop of 10% KOH or mineral oil. A positive smear will show an adult mite or mite ova, both of which are definitive (see Photo 45). Sometimes only the scybala or mite fecal balls are seen; these also support the diagnosis.
On the day of treatment, fresh clothing should be donned and bed linens should be changed. Furniture that is used frequently for lounging should be thoroughly vacuumed. Any clothing that has been worn and is launderable should be washed in the hot cycle. Any clothing that has been worn and is not launderable should be dry-cleaned. An alternative to dry-cleaning, for persons of limited financial resources, is to seal the exposed garments in a plastic bag for one week before reuse. Fastidious victims will tend to go overboard and it is important to set boundaries.
Permethrin in the form of a 5% cream formulation is currently the agent of choice in the treatment of scabies. For a typical case, it is applied from the neck down to all exter-
nal surfaces. You may have patients leave it on overnight and then shower it off. The application should be repeated one time only on the fourth to seventh day. This product is more effective, less irritating, and has less potential for toxicity than those previously available. Infants may on occasion require treatment of the head and neck areas, and patients with crusted scabies may require several treatments for cure. In elderly patients and in crusted scabies, special attention should be paid to the fingernails, which may be heavily infested. Subungual spaces should be manicured and medication should be applied.
Because symptoms persist for several days after effective therapy, patients must be cautioned not to continue treatment needlessly. For persisting symptoms, a topical steroid cream or a bland antipruritic ointment with 0.25% menthol and 0.5% camphor may be used. Other effective scabicides include gamma benzene hexachloride, benzyl benzoate, and 10% sulfur in yellow soft paraffin. These are inherently irritating to an already reactive skin surface. Gamma benzene hexachloride (lindane), if used to excess in children, has potential for substantial neurologic toxicity. It is no longer available in California.
In patients with crusted (Norweigian) scabies, for resistant cases, or for patients who cannot comply with topical regimens, an oral alternative is 200 ^g/kg ivermectinin two doses administered 1 week apart. Manicuring and hygiene procedures must still be observed. When combined with topical permethrin, this drug is even more effective.
Scabies must be considered in the differential diagnosis of any generalized pruritic skin disorder especially with a history of nocturnal itching that interrupts sleep. Atopic dermatitis, generalized drug reactions, and widespread impetigo all show common features. A high index of suspicion that leads to a search for primary lesions is important to maintain. Crusted scabies can simulate eczema, psoriasis, or on rare occasions, an ery-throderma.
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