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Scabies

Scabies is an infestation by the mite Sarcoptes scabiei, usually spread by skin-to-skin contact, and characterized by generalized intractable pruritus often with minimal cutaneous findings. The diagnosis may be missed easily and should be considered in a patient of any age with persistent generalized severe pruritus.

Causes of Scabies

Hypersensitivity of both immediate and delayed types occur in the development of lesions other than burrows. For pruritus to occur, sensitization to S.scabiei must take place. Among persons with their first infection, sensitization takes several weeks to develop; after reinfestation, pruritus may occur within 24 h. Various immunocompromised states or individuals with neurologic disease predisposed to crusted Norwegian scabies. Infestation is usually by only approximately 10 mites. In contrast, the number of infesting mites in crusted scabies may exceed a million.

Symptoms of Scabies

• Pimple-like irritations, burrows or rash of the skin, especially the webbing between the fingers; the skin folds on the wrist, elbow, or knee; the penis, the breast, or shoulder blades.
• Intense itching, especially at night and over most of the body.
• Small children or babies may have involvement of the face, scalp, palms of the hands, or soles of the feet.

Diagnosis

Clinical findings, confirmed, if possible, by microscopy (identification of mites, eggs, or mite feces). Assiduous search for burrows or papules should be made in every patient with severe generalized pruritus. Sometimes when the mite cannot be demonstrated, a "therapeutic test" will clinch the diagnosis.

Treatment

Principles of Treatment Infested individuals and close physical contacts should be treated at the same time, whether or not symptoms are present. Topical agents are more effective after hydration of the skin, i.e., after bathing. Application should be to all skin sites, especially the groin, around nails, behind ears, including face and scalp. Sexual partners and close personal or household contacts within last month should be examined and treated prophylactically.

Scabicides Choice of scabicide based on effectiveness, potential toxicity, cost, extent of secondary eczematization, and age of patient. Permethrin is effective and safe but costs more than lindane. Lindane is effective in most areas of the world, but resistance has been reported. Seizures have occurred when lindane was applied after a bath or used by patients with extensive dermatitis. Aplastic anemia after lindane use was also reported. No controlled studies have confirmed that two applications are better than one. Clean clothing should be put on afterwards. Clothing and bedding are decontaminated by machine-washing at 60°C. Pruritus can persist for up to 1 to 2 weeks after the end of effective therapy. After that time, cause of persistent itching should be investigated.

Recommended Regimens

Permethrin 5% Cream Applied to all areas of the body from the neck down. Wash off 8-12 h after application. Adverse events very low.

Lindane (g-Benzene Hexachloride) 1% Lotion or Cream Applied thinly to all areas of the body from the neck down; wash off thoroughly after 8h. Note: Lindane should not be used after a bath or shower, and it should not be used by persons with extensive dermatitis, pregnant or lactating women, and children younger than 2 years. Mite resistance to lindane has developed in North, Central, and South America and Asia. Low cost makes lindane a key alternative in many countries.

Alternative Regimens

Crotamiton 10% Cream Applied thinly to the entire body from the neck down, nightly for 2 consecutive nights; wash off 24 h after second application.

Sulfur 2 to 10% in Petrolatum Applied to skin for 2 to 3 days.

Benzyl Benzoate 10 and 25% Lotions Several regimens are recommended: swabbing only once; two applications separated by 10 min, or two applications with a 24-h or 1-week interval. 24 h after application, preparation should be washed off and clothes and bedding changed. The compound is an irritant and can induce pruritic irritant dermatitis, especially on face and genitalia.

Benzyl Benzoate with Sulfiram Several regimens are recommended: swabbing only once:

Esdepallethrine .63%

Malathion .5% lotion

Sulfiram 25% lotion Can mimic effect of disulfiram; no alcoholic drinks should be consumed for at least 48 h.

Ivermectin .8% lotion

Systemic Ivermectin Ivermectin, 200 µg/kg PO; single dose reported to be very effective for common as well as crusted scabies in 15 to 30 days. Two to three doses, separated by 1 to 2 weeks, usually required for heavy infestation or in immunocompromised individuals. May effectively eradicate epidemic or endemic scabies in institutions such as nursing homes, hospitals, and refugee camps. Not approved by USFDA or European Drug Agency.

Infants, Young Children, Pregnant/Lactating Women Permethrin or crotamiton regimens or precipitated sulfur ointment should be used with application to all body areas. Lindane and ivermectin should not be used.

Crusted Scabies Scabicides Lindane should be avoided because of risk of CNS toxicity. Multiple scabicide applications are required to all the skin. Treatment also should also be directed at removing scale/crusts that protect mites from scabicide; nails should be trimmed. Oral ivermectin combined with topical therapy is most effective. Control of dissemination is essential and includes isolation of patient, avoidance of skin-to-skin contact, use of gloves/gowns by staff, prophylactic treatment of contacts (entire institution and visitors or family members).

Decontamination of Environment Bedding, clothing, and towels should be decontaminated (machine washed or machine dried using heat cycle or dry-cleaned) or removed from body contact for at least 72 hours. Thorough cleaning of patient's room or residence.

Treatment of Eczematous Dermatitis Antihistamines Systemic sedating antihistamine such as hydroxyzine hydrochloride, doxepin, or diphenhydramine at bedtime.

Topical Glucocorticoid Ointment Applied to areas of extensive dermatitis associated with scabies.

Systemic Glucocorticoids Prednisone 70 mg, tapered over 1 to 2 weeks, gives symptomatic relief of severe hypersensitivity reaction.

Postscabietic Itching Generalized itchining that persists a week or more is probably caused by hypersensitivity to remaining dead mites and mite products. Nevertheless, a second treatment 7 days after the first is recommended by some physicians. For severe, persistent pruritus, especially in individuals with history of atopic disorders, a 14-day tapered course of prednisone (70 mg on day 1) is indicated.

Secondary Bacterial Infection Treat with mupirocin ointment or systemic antimicrobial agent.

Scabietic Nodules May persist in association with pruritus for up to a year after eradication of infestation. Intralesional triamcinolone, 5 to 10 mg/ml into each lesion, is effective; repeat every 2 weeks if necessary.