There are three varieties of lice specifically parasitic to humans: Pediculus humanus capitis (head louse), which infests the hair and scalp; Pthirus pubis (crab louse), which infests the pubic hair; and Pediculus humanus corporis (body louse). Affected patients may be asymptomatic or may have pruritus. The diagnosis is made via visual examination whereby crawling lice (nymphs and adults) and eggs (nits) are found on hair shafts. The treatment is topical pediculicides (including permethrin, malathion, benzyl alcohol, spinosad, and topical ivermectin) and wet combing to remove lice and nits. Lindane has an association with neurotoxicity, and its use should be avoided in children. Of note, nits may persist for several weeks following therapy. The differential diagnosis includes pseudonits (2- to 7-mm hair casts), psoriasis, cutaneous fungal infections, scabies, seborrheic dermatitis, and dandruff.
Management and Disposition
The diagnosis is clinical. Patients should be treated with topical pediculicides and educated on signs of resolution. Treatment failure is associated with noncompliance, reinfestation, and drug resistance. There is growing resistance to permethrin within the United States and Canada so other therapies should be considered if there is treatment failure with good compliance. Close contacts and those who share bedding should be treated prophylactically. Head lice generally do not survive for more than 2 days when off of a person. The nits die within 1 week if the temperature close to the scalp is not maintained. Clothing and items (eg, pillows, bedding, or stuffed animals) that cannot be washed should be dry-cleaned or sealed for 2 weeks in a plastic bag.
Children with head lice do not necessarily need to be excluded from school as many have had lice for several weeks and been attending school prior to diagnosis.
Combs and brushes can be disinfested by soaking in hot water (130°F or greater) for 5 to 10 minutes.
Although shaving hair is anecdotally an effective treatment, it can have adverse psychological effects.
Nits. Several small white cylindrical nits (louse eggs) are seen clinging to dark hair. (Photo contributor: Larry B. Mellick, MD.)
Lice Infestation. Multiple lice are seen in the hair of this patient. (Photo contributor: David Effron, MD.)