Updated: 10/29/2017

Lice

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Snapshot
  • PhotoA 7-year-old boy is brought to the pediatrician after he is noticed scratching his head at school. He reports that this itchiness has gone on for around 3 days now. His mom reports angrily that the school just notified them that several children had similar symptoms last week. Physical exam reveals several nits < 1 cm away from the base of the hair shaft. He is given topical permethrin and counseled that he can still go to school.
Introduction
  • Clinical definition
    • a very common ectoparasitic infestation of the scalp (pediculosis capitis or head lice) or pubic hair (pediculosis pubis or pubic lice)
      • pubic lice is also known as crabs
    • can also involve other hair-bearing areas, such as eyebrows or eyelashes
  • Epidemiology
    • incidence
      • common
    • demographics
      • head lice
        • girls > boys
        • healthy children, regardless of hygiene
        • adults with poor hygiene
        • less common in African Americans
      • pubic lice
        • teenagers and young adults
        • men who have sex with men
        • men > women
    • risk factors
      • household contact with infected children
      • overcrowded living conditions
  • Etiology
    • head lice
      • infestation with head louse Pediculus humanus capitis
      • transmitted via hair-to-hair direct contact
    • pubic lice
      • infestation with crab louse Pthirus pubis
      • transmitted via close physical or sexual contact
  • Pathogenesis
    • the life cycle of louse is the nit (egg), nymph (immature louse), and adult louse
    • females lay nits (eggs) that are attached to the hair
      • the farther away the nit from base of hair shaft, the older the infection
      • nits > 1 cm away from hair shaft may indicate an old, not active, infection
    • pruritus is caused by injection of saliva in the skin
  • Associated conditions
    • sexually transmitted diseases (in cases of pubic lice)
    • scabies
  • Prognosis
    • pruritus may linger until 10 days after treatment
    • may recur
Presentation
  • Symptoms
    • scalp or genital itching
    • a sensation of “crawling”
    • conjunctivitis if there is eyelash infestation
    • may be asymptomatic
  • Physical exam
    • examine by wet combing using a fine-tooth comb
    • live lice may be appreciated
    • more commonly, nits are found along at the base of the hair shaft 
      • nits < 1 cm is considered viable
      • often appear white
    • secondary skin lesions from scratching
      • excoriations or impetigo
Studies
  • Microscopic examination
    • may identify lice or nits on hair shafts
  • Making the diagnosis
    • most cases are clinically diagnosed
Differential
  • Scabies
  • Chiggers 
Treatment
  • Management approach
    • patients with head lice are treated with topical pediculicide initially or oral ivermectin in cases of treatment failure
      • children do not have to be kept from school
      • household members should be screened for head lice
  • Conservative
    • no shared clothing or hair accessories
    • wash all linens and clothing that could’ve come into contact with lice
  • Medical
    • occlusive topical agent
      • indications
        • for children with eyelash infestation
      • modalities
        • petroleum jelly
    • topical pediculicide
      • indications
        • for all patients
      • drugs
        • permethrin
        • ivermectin
        • dimethicone
    • oral ivermectin      
      • indications
        • topical treatment failure
Complications
  • Secondary bacterial infections may occur at site of excoriations

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