Scabies

Key Features

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 visible microscopically

• Red papules or nodules on the scrotum and on the penile glans and shaft are pathognomonic

General Considerations

• Caused by Sarcoptes scabiei

• Usually acquired through the bedding of an infested individual or by other close contact

• Facility-associated scabies is common, primarily in long-term–care facilities; patients are usually elderly and immunosuppressed

Clinical Findings

Symptoms and Signs

• Itching is almost always present and can be quite severe

• Lesions are more or less generalized excoriations with small pruritic vesicles, pustules, and "burrows" in the web spaces and on the heels of the palms, wrists, elbows, around the axillae, and on the breasts

• Often, burrows are found only on the feet, as they have been scratched off in other locations

• 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 posterior axillary line

• Usually spares the head and neck (though these areas may be involved in the elderly, and in patients with AIDS)

• Hyperkeratotic or crusted scabies presents as thick flaking scale

  • 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

Differential Diagnosis

• Pediculosis (lice)

• Atopic dermatitis (eczema)

• Contact dermatitis

• Arthropod bites (insect bites)

• Urticaria

• Dermatitis herpetiformis

Diagnosis

Laboratory Tests

• The diagnosis should be confirmed by microscopic demonstration of the organism, ova, or feces in a mounted specimen, best done on unexcoriated lesions from interdigital webs, wrists, elbows, or feet

• A No. 15 blade is used to scrape each lesion until it is flat

• Patients with crusted/hyperkeratotic scabies must be evaluated for immunosuppression (especially HIV and HTLV-1 infections) if no iatrogenic cause of immunosuppression is present

Treatment

Medications

• Treat mites and control the dermatitis, which can last months after eradication of the mites, with mid-potency topical corticosteroids (0.1% triamcinolone cream) (Table 6–2)

• Treatment consists of disinfestation; add systemic antibiotics for secondary pyoderma

• Permethrin 5% cream; treat with a single application for 8–12 h; may repeat in 1 week

• Ivermectin

  • Mass treatment can be beneficial to eradicate widespread infection

  • Dosage in immunocompetent persons: 200 mcg/kg orally

  • In immunosuppressed persons and those with crusted ...