SCABIES

SCABIES - Gary J. Silko, MD, MS
BASICS
DESCRIPTION
A contagious disease caused by infestation of the skin by the mite Sarcoptes scabiei, var. hominis
• System(s) Affected: Skin/Exocrine
EPIDEMIOLOGY
• Predominant age: Children and young adults
• Predominant sex: Male = Female
Incidence
Worldwide incidence is 300 million cases per year.
Prevalence
Common in the US, although number of cases per year is declining as the epidemic, which began in 1971, passed its peak (1986).
RISK FACTORS
• Personal skin-to-skin contact (e.g., sexual promiscuity, crowding, poverty, nosocomial infection)
• Immunocompromised patients including those with HIV/AIDS
• Atopic eczema
ETIOLOGY
Sarcoptes scabiei, var. hominis

DIAGNOSIS
SIGNS AND SYMPTOMS
• Generalized itching (often severe)
• Nocturnal pruritus
• Burrows in finger webs and sides of fingers
• Excoriated and nonexcoriated papules on hands, waistline, penis, scrotum, buttocks, and flexor surfaces of wrist, elbow, and anterior axillary folds
• Vesicles and papules (discrete)
• Secondary erosions or excoriations
• Pustules (if secondarily infected)
• Scaling
• Erythema
• Nodules in covered areas (buttocks, groin, axillae)
• Atypical infestations in immunosuppressed patients
ALERT
Geriatric Considerations
The elderly often itch more severely, despite fewer cutaneous lesions, and are at risk for extensive infestations, perhaps related to a decline in cell-mediated immunity. May see back involvement in those who are bedridden
Pediatric Considerations
Infants often have more widespread involvement. They are occasionally infested on the face and scalp (rare for adults). Vesicular lesions on the palms and soles are also more commonly seen. When treating infants with permethrin, the entire body should be treated.
TESTS
Lab
CBC, although rarely needed, will frequently demonstrate eosinophilia.
Diagnostic Procedures/Surgery
• Examination of skin with magnifying lens
- Look for typical burrows in finger webs, on flexor aspects of the wrists, and penis.
- Look for a dark point at the end of the burrow (the mite).
- The mite can be extracted with a 25-gauge needle and examined microscopically.
• Mineral oil mounts
- Place a drop of mineral oil over a suspected lesion. Nonexcoriated papules or vesicles may also be sampled.
- Scrape the lesion with a no. 15 surgical blade.
- Examine under a microscope for mites, eggs, egg casings, or feces.
- Scraping from under fingernails may often be positive.
• Potassium hydroxide (KOH) wet mount
- Transfer skin scrapings directly to a glass slide, add a drop of KOH, and apply a cover slip.
- Examine the slide for diagnostic material.
- If none is evident, heat slide gently to separate squamous cells and re-examine.
• Burrow ink test
- If burrows are not obvious, apply blue-black ink to an area of rash. Wash off the ink with alcohol. A burrow should remain stained and become more evident.
- Then apply mineral oil, scrape, and observe microscopically as previously noted.
Pathological Findings
Skin biopsy of a nodule (although rarely performed) will reveal portions of the mite in the corneal layer.
DIFFERENTIAL DIAGNOSIS
• Atopic dermatitis
• Dermatitis herpetiformis
• Eczema
• Insect bites
• Papular urticaria
• Pediculosis corporis
• Pityriasis rosea
• Prurigo
• Pyoderma
• Seborrheic dermatitis
• Syphilis
TREATMENT
GENERAL MEASURES
• Treat all intimate contacts and close household and family members.
• Wash all clothing, bed linen, and towels in a normal wash cycle.
Diet
No special diet
Activity
Full activity
MEDICATION (DRUGS)
First Line
• Permethrin ((Elimite, Acticin) 5% cream (Nix) 1% cream rinse)
- Considered by many to be the drug of choice for scabies
- Cream is applied into the skin from the neck to the soles of the feet with particular attention given to skin creases. It is left on for 8-14 hours, and then thoroughly washed off. Thirty grams is usually adequate for an adult. A 2nd application 1 week later is sometimes recommended. (1)[C]
• Lindane (Kwell, Scabene) 1%
- Available in lotion, cream, and shampoo. The cream or lotion should be applied to all skin surfaces from the neck down and washed off 8-12 hours later. 2 applications 1 week apart are recommended by some physicians. (1)[C]
• Crotamiton (Eurax) 10%
- Cream is applied into the skin from the head to the soles of the feet, left on for 8-14 hours, and then thoroughly washed off. It is believed to be less toxic than Lindane, but perhaps slightly less effective; therefore, application 5 nights in a row is advised. (2)[C]
• Contraindications
- Lindane should be avoided in children who are premature, malnourished, or emaciated and those with severe underlying skin disease or a history of seizure disorders.
• Precautions
- Patients should be cautioned not to overuse the medication when applying it to the skin.
- For medications other than permethrin, patients should use a 2nd application only when specifically advised to do so by their physician.
- Lindane should be used cautiously in immunocompromised patients.
• Significant possible interactions
- Avoid lindane for patients on medications that lower the seizure threshold, such as tricyclic antidepressants.
ALERT
Pregnancy Considerations
Permethrin and lindane are category B drugs. Until more information is available, precipitated sulfur appears to be the safest treatment in pregnant or lactating women.
Pediatric Considerations
The US Food and Drug Administration (FDA) recommends caution when using lindane in patients who weigh 50 kg. It is not recommended for infants and is contraindicated in premature infants.
Second Line
• Precipitated sulfur 6% in petroleum
- Applied to the entire body from the neck down for 3 nights. It is malodorous and messy, but is thought to be safer than lindane, especially in infants 6 months and safer than permethrin in infants 2 months.
• Ivermectin (Mectizan)
- 100-200 ug/kg in 1 or 2 divided doses.
- May need higher doses or in combination with topical scabicide for HIV-positive patients. (1)[B]
FOLLOW-UP
DISPOSITION
Outpatient care
PROGNOSIS
• Lesions begin to regress in 1-2 days along with the worst itching.
• Some itching and dermatitis commonly persists for 10-14 days and can be treated with antihistamines and/or topical or oral corticosteroids.
• Nodular lesions may persist for several weeks, perhaps necessitating intralesional or systemic steroids.
• Some instances of lindane-resistant scabies have now been reported. These do respond to permethrin.
COMPLICATIONS
• Eczema
• Pyoderma
• Postscabetic pruritus
• Nodular scabies
PATIENT MONITORING
Recheck patient at weekly intervals only if rash or itching persists. Scrape new lesions and retreat if mite or products found.
REFERENCES
1. Freedberg IM et al. Fitzpatrick's Dermatology in General Medicine. 6th ed. New York, NY: McGraw-Hill; 2003: 2283-2285.
2. James WD, Berger TG, Elston DM. Andrews' Diseases of the Skin. 10th ed. Philadelphia, PA: WB Saunders; 2006;452-453.
MISCELLANEOUS
See also: Insect bites and stings