Scabies

1. Epidemiology
   1. Most common in children under age 2 years
   2. Endemic to tropical areas
2. Pathophysiology
   1. Caused by mite infestation: Sarcoptes scabiei
   2. Life cycle of female mite (30 days)
      1. Female mite burrows into skin to lay eggs
         1. Lays 10 to 25 eggs
         2. Dies after laying eggs
      2. Eggs hatch within 3-4 days
      3. Scabies larvae mature into adults in 14-17 days
      4. Mites can live up to 3 days without a human host
      5. Mites can complete life cycle without host symptoms
   3. Transmission with any contact including with fomites
      1. Prolonged skin contact (usually not a handshake)
         1. Hospitals and Nursing Homes
         2. Day cares
      2. Household contact
      3. Sexual contact
      4. Shared clothing or bedding
   4. No transmission from pets with Scabies (mange)
      1. Mite may be passed from pet but does not survive
      2. Short-term itching may occur but resolves in days
3. Symptoms
   1. Severe itch at incubation (immune reaction to feces)
   2. Symptoms worse at night
4. Signs
   1. Characteristics
      1. Initial: Tiny erythematous Papules
      2. Next: Vesicles or Pustules may form
      3. Pathognomonic: Burrow (variably present but uncommon)
         1. Consider coloring lesions with magic marker and then washing the area
            1. Marker will infiltrate the burrows, and the burrows will be more evident
      4. Secondary to scratching: Excoriations, crusts
      5. Variants in immunocompromised patients
         1. Hyperkeratotic crusted Scabies
   2. Distribution
      1. Infants: Face and scalp involvement
      2. Children
         1. Spares face and scalp
         2. Hands (especially web spaces)
         3. Axillae
         4. Antecubital fossa
      3. Adults (includes sites for children above)
         1. Genitalia
         2. Female Breast
         3. Gluteal crease
         4. Waistband
5. Diagnosis
   1. Search for burrows holding gravid female mite
      1. Often found on nipples, axillae, hands and genitalia
      2. Find newest lesions and least disturbed skin
      3. Check beneath finger nail edge
   2. Scrape Burrow or other lesions onto slide with #15 blade
      1. Observe under low power in oil for:
         1. Mite
         2. Eggs
         3. Scybala (Mite feces)
      2. Potassium Hydroxide (KOH)
         1. Dissolves scybala
6. Management
   1. General
      1. Treat family members who sleep in same room
      2. Wash in hot water and dry all clothing and bedding used in the last 48 hours
      3. Itching will persist up to 1 month after treatment
         1. Pruritus clears as skin sloughs mite debris
         2. See Pruritus Management for general measures
         3. Consider Topical Steroid after treatment
   2. Body (follow links to agents below regarding usage)
      1. First Line
         1. Permethrin (Elimite) 5% cream
            1. May be used in infants over age 2 months
            2. Pregnancy Category B
      2. Other agents
         1. Lindane (Kwell) 1% Lotion
            1. Avoid due to neurotoxicity
            2. Higher risk with broken skin and young children
            3. Higher resistance rates than other agents
         2. Precipitated Sulfur in petrolatum (compounded)
            1. Has been used in newborns, pregnancy, Lactation
            2. No safety or efficacy data available
            3. Applied head to toe
               1. Leave on 24 hours
               2. Repeat application daily for 3 days total
            4. Change bed linen as treatment is completed
            5. Stings!
      3. Complicated or refractory cases
         1. Ivermectin
            1. Used in Scabies refractory to Permethrin
            2. Used in generalized crusted Scabies
         2. Crotamiton (Eurax) 10% cream
            1. Used in nodular Scabies
   3. Genital Scabies
      1. Permethrin 5% cream, wash off in 8-14 hours
7. References
   1. Angel (2000) Pediatr Clin North Am 47(4):921-35
   2. Finders (2004) Am Fam Physician 69(2):341-50
   3. Potts (2001) Postgrad Med 110(1):57-64
   4. Roos (2001) Drugs 61(8):1067-88