Definition
A.Scabies is a contagious skin infestation by the mite Sarcoptes scabiei.
Incidence
A.Scabies occurs mainly in individuals in close contact with many other individuals, such as nursing home residents. It is rare among African Americans.
Pathogenesis
A.Scabies is transmitted through close contact with an individual who is infested with the mite S. scabiei. Transmission may occur through sexual contact or contact with miteinfested clothing or sheets. The fertilized female mite burrows into the stratum corneum of a host and deposits eggs and fecal pellets. Larvae hatch, mature, and repeat the cycle.
B.A hypersensitivity reaction is responsible for the intense pruritus.
Predisposing Factors
A.Close contact with large numbers of individuals.
B.Institutionalization.
C.Poverty.
D.Sexual promiscuity.
Common Complaints
A.Intense itching, worse at night.
B.Skin excoriation.
C.Generalized pruritus.
D.Rash.
Other Signs and Symptoms
A.Mites burrow in finger webs, at wrists, in the sides of hands and feet, at the axilla and buttocks, and in the penis and scrotum in males.
B.Discrete vesicles and papules, distributed in linear fashion.
C.Erythema.
D.Secondary bacterial infections due to scratching (pustules and pinpoint erosions).
E.Nodules in covered areas (buttocks, groin, scrotum, penis, axilla), which may have slightly eroded surfaces that persist for months after mites have been eradicated
F.Diffuse eruption that spares face.
Subjective Data
A.Elicit information regarding housing conditions, close contact, or sexual contact with potentially infected individuals.
B.Question the patient regarding onset, duration, and location of itching.
Physical Examination
A.Check temperature.
B.Inspect:
1.Examine all body surfaces with patient unclothed.
2.Use a magnifying lens to identify characteristic burrows in finger webs, wrists, and penis.
3.Inspect adult pubic area for lesions.
Diagnostic Tests
A.Three findings are diagnostic of scabies:
1.Microscopic identification of S. scabiei mites.
2.Eggs.
3.Fecal pellets (scybala).
B.Burrow identification: Ink the suspected area with a blue or black felt-tipped pen, then wipe with an alcohol swab. The burrow absorbs the ink, while the surface ink is wiped clean.
C.A tiny black dot may be seen at the end of a burrow, which represents the mite, ova, or feces, and can be transferred by means of a 25-gauge hypodermic needle to immersion oil on a slide for microscopic identification.
D.Place a drop of mineral oil on a suspected lesion, scrape lesion with a #15 blade, and transfer the shaved material to a microscope slide for direct examination of the mite under low power.
Differential Diagnoses
A.Scabies.
B.Atopic dermatitis.
C.Insect bites.
D.Pityriasis rosea.
E.Eczema.
F.Seborrheic dermatitis.
G.Syphilis.
H.Pediculosis.
I.Allergic or irritant contact dermatitis.
Plan
A.General interventions:
1.Implement comfort measures to reduce pruritus.
2.Treat secondary bacterial infection(s) with antibiotics.
3.Household members should be treated simultaneously as a prophylactic measure and to reduce the chance of reinfection.
4.The patient should be advised that pruritus may continue for up to a week even with a successful treatment due to local irritation.
B.See Section III: Patient Teaching Guide Scabies.
C.Pharmaceutical therapy:
1.First line of therapy, due to its low toxicity, is 5% permethrin (Elimite cream) applied to all body areas from neck down and washed off in 8 to 14 hours. One application is highly effective, but some dermatologists recommend retreatment in 1 week.
2.Alternative therapy is lindane (Kwell) cream, applied to all skin surfaces from the neck down and washed off in 8 to 12 hours. Some dermatologists re-treat in 7 days.
3.An oral dose of the anthelmintic agent ivermectin (200 mcg/kg) followed by a repeat dose in 1 to 2 weeks has been shown to be effective and to rapidly control pruritus in healthy patients and HIV patients.
4.Diphenhydramine (Benadryl) 25 to 50 mg may be given by mouth every 4 to 6 hours if indicated for pruritus. Other nonsedating antihistamines may be used. Toxicity is usually a result of patient overtreatment (failure to follow prescribed regimen). Advise the patient of this danger.
Follow-Up
A.Follow up in 2 weeks to assess treatment response.
Consultation/Referral
A.Consult or refer the patient to the physician if, at 2-week follow-up, pharmaceutical therapy has been ineffective.
Individual Considerations
A.Pregnancy:
1.Permethrin is preferred to lindane in pregnant and/or lactating women due to decreased toxicity.
2.Patient should be warned of its potential to cause neurotoxicity and convulsions with overuse (more than two treatments).
B.Partners:
1.All intimate contacts within the past month and close household and family members should be treated.
C.Geriatrics:
1.The elderly tend to have more severe pruritus despite fewer lesions.
2.They are at risk for extensive infections due to an agerelated decline in immunity.
3.The excoriations may become severe and may be complicated by cellulitis.
4.Geriatric red flags:
a.Avoid first-generation anticholinergics because of risk of confusion, dry mouth, constipation, and other anticholinergic effects or toxicity.
b.Geriatric patients that have dementia or declining functional abilities need a thorough home environment assessment and an evaluation for any issues of neglect or abuse.