Короста

Scabies is caused by the mite Sarcoptes scabiei var. hominis, an obligate human parasite that lives in burrowed tunnels in the stratum corneum. Scabies is easily transmitted from person to person through physical contact; animal and fomite transmission probably also occurs. The primary risk factor is crowded conditions (as in schools, shelters, barracks, and some households); there is no clear association with poor hygiene.

For unknown reasons, crusted scabies is more common among patients who are immunosuppressed (eg, those with HIV infection, hematologic cancer, chronic corticosteroid or other immunosuppressant use), patients with severe physical disabilities or intellectual disability, and Australian Aborigines. Infestations occur worldwide (1). Patients in warm climates develop small erythematous papules with few burrows. Severity is related to the patient’s immune status, not geography.

Scabies

Зображення

Photo courtesy of Karen McKoy, MD.

The primary symptom of scabies is intense pruritus, classically worse at night, although that timing is not specific to scabies.

Класична короста

Erythematous papules initially appear in finger web spaces, flexor surfaces of the wrist and elbow, axillary folds, along the belt line, or on the lower buttocks. Papules can affect any area of the body, including the breasts and penis. The face remains uninvolved in adults. Burrows, usually on the wrists, hands, or feet, are pathognomonic for disease, manifesting as fine, wavy, and slightly scaly lines several millimeters to 1 cm long. A tiny dark papule—the mite—is often visible at one end. In classic scabies, people usually have only 10 to 12 mites. Secondary bacterial infection commonly occurs.

Класична короста

Сховати деталі

A pruritic, pustular rash in the webbing between fingers is the hallmark of classic scabies.

Image courtesy of the Public Health Image Library of the Centers for Disease Control and Prevention.

Signs of classic scabies may be atypical. In Black people and other people with dark skin, scabies can manifest as granulomatous nodules. In infants, the palms, soles, face, and scalp may be involved, especially in the posterior auricular folds. In older patients, scabies can cause intense pruritus with subtle skin findings, making it a challenge to diagnose. In patients who are immunosuppressed, there may be widespread nonpruritic scaling (particularly on the palms and soles in adults and on the scalp in children).

Дитяча короста

Сховати деталі

In infantile scabies, pustules on the soles and palms are common.

© Springer Science+Business Media

Інші форми

Crusted scabies (Norwegian scabies) is due to an impaired host immune response, allowing mites to proliferate and number in the millions; scaling erythematous patches often involve the hands, feet, and scalp and can become widespread.

Crusted (Norwegian) Scabies

Сховати деталі

This photo shows diffuse scaling and hyperkeratotic plaques in a patient with HIV and crusted scabies.

© Springer Science+Business Media

Nodular scabies is more common among infants and young children and may be due to hypersensitivity to retained organisms; nodules are usually erythematous, 5 to 6 mm, and involve the groin, genitals, axillary folds, and buttocks. Nodules are hypersensitivity reactions and may persist for months after eradication of mites.

Вузлова короста

Сховати деталі

Nodular scabies are shown in this photo as multiple brownish red papules on the axilla.

© Springer Science+Business Media

Bullous scabies occurs more commonly among children. When it occurs in older adults, it can mimic bullous pemphigoid, resulting in a delay in diagnosis.

Scalp scabies occurs in infants and immunocompromised people and can mimic dermatitis, particularly atopic dermatitis or seborrheic dermatitis.

Scabies incognito looks like a widespread eczema and occurs in patients who use topical corticosteroids.

• Clinical evaluation

• Burrow scrapings

Diagnosis of scabies is suspected by physical findings, especially burrows, and itching that is out of proportion to physical findings and similar symptoms among household contacts.

Confirmation is by finding mites, ova, or fecal pellets on microscopic examination of burrow scrapings; failure to find mites is common and does not exclude scabies. Scrapings should be obtained by placing glycerol, mineral oil, or immersion oil over a burrow or papule (to prevent dispersion of mites and material during scraping), which is then unroofed with the edge of a scalpel. The material is then placed on a slide and covered with a coverslip; potassium hydroxide should be avoided because it dissolves fecal pellets.

Imaging and magnification of the skin using a hand-held instrument (dermoscopy) can be done to help identify scabies.

• Topical permethrin, or other topical scabicides

• Sometimes oral ivermectin

Primary treatment is topical or oral scabicides (1) (see table Treatment Options for Scabies). Permethrin is the first-line topical medication.

Older children and adults should apply permethrin to the entire body from the neck down and wash it off after 8 to 14 hours. Lindane is no longer recommended because it can be neurotoxic (2). Treatments should be repeated in 7 days.

For infants and young children, permethrin should be applied to the head and neck, avoiding periorbital and perioral regions. Special attention should be given to intertriginous areas, fingernails, toenails, and the umbilicus. Mittens on infants can keep permethrin out of the mouth.

For adults and children 4 years of age and older, spinosad 0.9% topical suspension should be applied to the entire cutaneous surface from the neck down, including the soles and feet. In bald patients, the suspension should be applied to the scalp, forehead, hairline, and temples. The suspension should be allowed to dry for 10 minutes before getting dressed and then left on the skin for 6 hours before showering or bathing. Treatment should be repeated in 1 week (3).

Precipitated sulfur 6 to 10% in petrolatum is an alternative therapy typically reserved for infants < 2 months of age or pregnant individuals. It is applied for 24 hours for 3 consecutive days, is safe and effective.

Ivermectin is indicated for patients who do not respond to topical treatment, are unable to adhere to topical regimens, or are immunocompromised with Norwegian scabies. Ivermectin has been used with success in epidemics involving close contacts, such as nursing homes.

Close contacts should also be treated simultaneously, and personal items (eg, towels, clothing, bedding) should be washed in hot water and dried in a hot dryer or isolated (eg, in a closed plastic bag) for at least 3 days.

Pruritus can be treated with corticosteroid ointments and/or oral antihistamines (eg, hydroxyzine 25 mg orally 4 times a day). Secondary infection should be considered in patients with weeping, yellow-crusted lesions and treated with the appropriate systemic or topical antistaphylococcal or antistreptococcal antibiotic.

Symptoms and lesions take up to 3 weeks to resolve despite killing of the mites, making failed treatment due to resistance, poor penetration, incompletely applied therapy, reinfection, or nodular scabies difficult to recognize. Skin scrapings can be done periodically to check for persistent scabies.