Updated: 12/16/2021

Lice

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https://upload.medbullets.com/topic/120063/images/head-lice-on-head.jpg
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https://upload.medbullets.com/topic/120063/images/pediculus_humanus_var_capitis.jpg
  • Snapshot
    • A 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
    • Associated conditions
      • sexually transmitted diseases (in cases of pubic lice)
      • scabies
  • 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
    • 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
    • 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
  • 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
  • Prognosis
    • Pruritus may linger until 10 days after treatment
    • May recur
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