Description
- common pediatric ectoparasite infestation
Also called
- pediculosis capitis
Who is most affected
- healthy children aged 3 to 12 years regardless of hygiene
- girls > boys
- household contacts of infested children
- adults with poor personal hygiene
- less common in African Americans
Incidence/Prevalence
- common, estimated 6 to 12 million cases in the United States per year
- reported prevalence 3.4% to 35%
Likely risk factors
- head-to-head contact, especially in schools, child care centers, or “sleepover” camps
- household contacts
- overcrowded living conditions
Possible risk factors
- hair traits
Factors not associated with increased risk
- hygiene (in children)
- length of hair
- frequency of brushing or shampooing
- socioeconomic class
Associated conditions
- other louse infestation or scabies (especially in indigent, homeless, or refugee populations)
Causes
- head louse Pediculus humanus var capitis
Pathogenesis
- life cycle repeats every 3 weeks
- female louse lives 3 to 4 weeks, lays up to 10 eggs (nits) daily
- eggs initially translucent, attached to base of hair shaft by glue-like substance from louse
- empty egg casings are white, viable nits pigmented
- eggs incubate (need heat of scalp) and hatch in 7 to 12 days
- female nymphs grow for about 9 to 12 days, then mate and lay eggs
- no transmission of other disease agents to humans
History
Chief concern (CC)
- scalp pruritus (due to injected louse saliva)
- “something crawling on my head”
- often asymptomatic
Social History (SH)
- ask if any cases of head lice at child’s school or day care
Physical
HEENT
Continue Reading
- primary findings are nits or adult lice (may require magnifying lens)
- nits at proximal ends of hair shafts
- viable nits most easily seen at nape of neck or behind ears at hairline
- height of nits above scalp due to hair growth indicates duration of infestation (1 cm/month)
- number of lice found may vary by cultural hair grooming practices
- secondary skin reactions to lice or scratching
- excoriation
- secondary bacterial infections
Neck
- posterior cervical local adenopathy if secondary skin infection
Making the diagnosis
- presence of live adult louse, nymphs, or viable-appearing eggs (nits) on head
- nits appear viable if found <1 cm of scalp, firmly attached to hair, and have microscopic “eye spot”
Differential diagnosis
- other causes of scalp pruritus
- irritation from hairstyling products
- allergic contact dermatitis
- seborrheic dermatitis
- dead eggs or empty egg gases
- “pseudo-nits” — nodules resembling nits (can be easily separated from hair)
- dandruff
- dried hairspray
- dirt, lint, sand
- white piedra — fungi (Trichosporon beigelii)
- hair casts — desquamated cylindrical epithelial cell plug that encircles hair, easily movable
