ESSENTIALS OF DIAGNOSIS
Generalized very severe itching but infestation usually spares the head and neck.
Burrows, vesicles, and pustules, especially on finger webs and in wrist creases.
Mites, ova, and brown dots of feces (scybala) visible microscopically.
Red papules or nodules on the scrotum and on the penile glans and shaft are pathognomonic.
Scabies is caused by infestation with Sarcoptes scabiei, affecting over 200 million people worldwide. Close physical contact for 15–20 minutes with an infected person is the typical mode of transmission. However, scabies may be acquired by contact with the bedding of an infested individual. Facility-associated scabies is common, primarily in long-term care facilities, and misdiagnosis is common. Index patients are usually elderly and immunosuppressed. When these patients are hospitalized, hospital-based epidemics can occur. These epidemics are difficult to eradicate since many health care workers become infected and spread the infestation to other patients.
Itching is almost always present and can be severe. The lesions consist of more or less generalized excoriations with small pruritic vesicles, pustules, and “burrows” in the interdigital spaces of the hands and feet, on the heels of the palms, wrists (Figure 6–35), elbows, umbilicus, around the axillae, on the areolae in women, or on the penile shaft and scrotum in men (eFigure 6–36). The burrow appears as a short irregular mark, 2–3 mm long and the width of a hair. Characteristic nodular lesions may occur on the scrotum or penis and along the posterior axillary line. The infestation usually spares the head and neck (though these areas may be involved in infants, older adults, and patients with AIDS).
Scabies. (Used, with permission, from TG Berger, MD, Dept Dermatology, UCSF.)
Hyperkeratotic or crusted scabies presents as thick flaking scale (eFigure 6–83). These areas contain millions of mites, and these patients are highly infectious. Pruritus is often absent. Patients with widespread hyperkeratotic scabies are at risk for superinfection with S aureus, which in some cases progresses to sepsis if left untreated. Crusted scabies is the cause of 83% of scabies outbreaks in institutions.
Crusted scabies. (Used, with permission, from Lindy Fox, MD.)
The diagnosis should be confirmed by microscopic demonstration of the organism, ova, or feces in a mounted specimen (eFigure 6–84), examined with tap water, mineral oil, or KOH. Best results are obtained when multiple lesions are scraped, choosing the best unexcoriated lesions from interdigital webs, wrists, elbows, or feet. A No. 15 blade is used to scrape each lesion until it is ...