Scabies
Gonzalo De Toro, MD
Key Facts
Etiology/Pathogenesis
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Caused in humans by scabies mite Sarcoptes scabiei variety hominis
Clinical Issues
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Predilection for interdigital areas and flexures, waist, ankles, and intergluteal fold
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3 different clinical forms
Microscopic Pathology
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Diagnostic finding is presence of mite, feces, or eggs in stratum corneum
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Many levels may be necessary
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Superficial and deep infiltrate of lymphocytes, histiocytes, mast cells, and eosinophils
Top Differential Diagnoses
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Dermal hypersensitivity reactions
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Lymphomatoid papulosis
Scabies presented in this patient as multiple, excoriated papules  and burrows  on the hand. |
Positive KOH scraping from a patient with Norwegian (crusted or keratotic) scabies shows a large scabietic mite  with an oval egg casing to the left  . |
TERMINOLOGY
Synonyms
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Itch mite infestation, “7-year itch”
Definitions
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Ectoparasitic infestation with about 300,000,000 cases worldwide each year
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Common predisposing factors are overcrowding, immigration, poor hygiene, poor nutritional status, homelessness, dementia, and sexual contact
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Direct skin-to-skin contact for 15-20 minutes is needed to transfer mites from 1 person to another
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