“Scabies.” I know that you are already itching. Soon it will be uncontrollable. The Ped EM Morsels have covered several conditions that cause pruritus (ex, Eczema, Tinea Capitis, Hyperbilrubinemia) as well as a general approach to Rashes, but nothing will make a patient, or a clinician, more uncomfortable than the potential for the patient having Scabies!

Scabies: The Ultimate Itch

• Scabies is a skin disease causes by infestation of a mite, Sarcoptes scabiei var. hominis.
• The mite burrows into the top layers of skin, where the female will lay her eggs.
• After 4-6 weeks, patients develop an allergic type reaction to the mite’s proteins and feces.
• Intense pruritus leads to problems!
  • The itch leads to lots of scratching.
  • Lots of scratching leads to mechanical injury to the skin.
  • Skin injury allows for secondary bacterial infections (Staph and Strep) and complications:
    • Suppurative complications
      • Impetigo
      • Cellulitis
      • Subcutaneous abscesses
      • Sepsis
    • Non-Suppurative complications
      • Acute post-streptococcal glomerulonephritis
        • ~50% of acute post-strep GN in tropical settings is due to skin infection. [WHO]
      • Rheumatic heart disease
        • Scabies related skin infections offers an explanation of high rheumatic heart disease rates in countries with low rates of strep pharyngitis. [Parks, 2012]

Scabies: Under-appreciated

• Scabies is more than a nuisance and control is a challenge. [Engelman, 2013]
• Scabies is one of the most prevalent skin conditions worldwide.
  • 130 MILLION people have scabies at any one time worldwide. [WHO]
  • Effects ~5-10% of children in developing countries.
• Effects people from every country, but is most prevalent in at risk populations:
  • Populations with poor access to resources
  • Young
  • Elderly

Scabies: Different in Children

• Children may present with different clinical findings than adults.
• Infants are more likely to have: [Boralevi, 2014]
  • Facial / Scalp involvement
  • Palm and plantar lesions
  • Dorsum of the forefoot lesions!
• Children (2-15 yrs) are more likely to have relapses. [Boralevi, 2014]
• Burrows are observed in all age groups, but not necessary for the diagnosis.
• Nodules also are seen in all age groups, but in infants more often in axilla and back locations.

• Look actively for burrows, axillary nodules and involvement in the soles, dorm of the forefoot, and scalp/face! [Boralevi, 2014]

Scabies: Treatments

• No treatment is perfect.
• Summarized nicely by Mousey and McCarthy [2013]
• Permethrin 5% Topical
  • 1st line in many countries
  • Good safety profile and effective
  • Recommended to apply twice (2nd treatment 1 week after 1st treatment) to kill residual eggs that subsequently hatch.
  • Limitation = expensive cost
• Benzyl Benzoate Topical
  • Dosage: Adults – 25%; children 10-12.5%
  • Highly efficacious
  • Inexpensive
  • Not available in the USA.
  • Limitation = significant skin irritation that occurs immediately, limiting tolerance
• Ivermectin
  • Off-label in most countries, but known to be effective.
  • Oral 
    • Dose = 200 micrograms/kg; two doses, 2nd dose 1 week after 1st.
    • Used to treat Crusted Scabies (high mite burden) and for treatment of large groups of patients.
    • Not approved for kids < 15 kg or in pregnant / lactating women (who often have high burden of disease)
  • Topical
    • Dose = 1%
    • More effective than single dose of oral.
• Other treatment considerations
  • Antihistamines
  • Avoidance of Lindane – less effective than other therapies and has adverse neurologic sequelae.
  • Topical corticosteroids are not recommended as they may mask treatment failure.
  • Treatment Failure:
    • Challenging to determine as clinical pruritus will continue even after appropriate therapy.
    • Most likely causes of treatment failure:
      • Inadequate therapy or application of topical treatment
      • Re-infestation (so consider treatment of contacts)
      • Mite resistance (less likely than the 1st two).

References