Head Lice (Pediculosis Capitis)

Head Lice (Pediculosis Capitis, see also Chapter 29: Bites, Stings, and Infestations)

Pediculosis capitis (head lice) is a common parasitic infestation in school-aged children, occasionally occurring in epidemics.
Lice spend their entire life cycle on the human and feed exclusively on human blood.
Transmission occurs by head-to-head contact or via shared combs, brushes, hats, or other personal items.
Head lice occur more often in girls and women; they are unusual in African-Americans, but not in African blacks.

Patients usually complain of intense scalp itch but occasionally children with head lice may be asymptomatic.
There are no primary lesions; however, secondary crusts and eczematous dermatitis resulting from scratching may be present.
Itching may be delayed 4 to 6 weeks.
Female louse lays 10 eggs per day the egg (nit) tightly adheres to the hair shaft at the scalp eggs hatch in 7 to 12 days becomes an adult (after three nymph stages) in 9 to 12 days. Female lice live for 3 to 4 weeks.
Nits (louse eggs) are firmly stuck on to scalp hairs and can be easily visualized with side lighting. Nits can be seen at varying distances from the scalp.
Occasionally live living lice can also be seen on the scalp (Fig. 9.13).

Knowledge of an epidemic at school generally alerts parents or school nurses to look for evidence of lice.
White nits may be very obvious on a background of darker hair.
A hair may be plucked and examined for nits using the low power of a microscope (Fig. 9.14).
A nit is attached to the base of a hair shaft when the egg is first laid and remains cemented to the growing hair so in general the distance from the scalp can give an idea of how long the infestation has been present.

Differential Diagnosis

Atopic Dermatitis of the Scalp

Seborrheic Dermatitis or Dandruff

Helpful Hints

Patients being treated for lice should be instructed to wear hair pulled back.
In a patient who has been treated for lice, nits attached more than 1 cm from the scalp are typically nonviable.
Items that cannot be washed or dry cleaned should be placed in a sealed bag for 2 weeks.

Management

General Principles

First-line treatment for head lice is a topical pediculicide.
All treatments should be repeated after 1 week (regardless of what package instructions suggest), in order to assure killing any nits that may have survived and prevent reinfestation from fomites.
Pediculicides have two modes of action: neurotoxic or physical.
Despite recommendations against it by the American Academy of Pediatrics, many schools still have a “no nit” policy whereby a child will not be allowed back to school unless the scalp is completely nit free; thus, manual removal of nits is important part of the treatment.
Nits are best removed manually with a fine-tooth metal comb.
All recently used clothing, hats, bedding, and towels as well as combs, brushes, and hair clips should be washed in hot water.
Other household members should be evaluated for lice and treated simultaneously.

Topical Treatments: Neurotoxic Mode of Action

Permethrin 1% cream or rinse (Nix Creme Rinse, Acticin) is available over the counter.

How to use: Wash hair, towel dry, apply cream rinse leave on for 10 minutes then rinse, repeat in 7 days.

Permethrin 5% Cream (Elimite Cream) is available as a prescription.

How to use: Apply to dry hair, leave on overnight (12 hours) under an occlusive shower cap, repeat in 7 days.
High rates of resistance (even to the higher concentrations) have limited its usefulness.

Pyrethrins with piperonyl butoxide (RID, Pronto, Licide) available over the counter.

How to use: Apply to dry hair, leave on for 10 minutes then rinse off, repeat in 7 days.
Treatment failures are now commonplace due to resistance.
Allergic reactions can develop in patients sensitive to chrysanthemums, ragweed, and related plants.

Malathion 0.5% Lotion (Ovide) available as a prescription.

This agent is considered the most effective treatment for head lice.
How to use: Apply to dry hair, massage into the scalp and leave on for 8 to 12 hours, repeat in 7 days.
Caution: Ovide Lotion is flammable. Treated areas that are wet with this product should be kept away from open flames and electric heat sources such as hair dryers.
Some resistance has been reported in the United Kingdom, but not in the United States.

Lindane 1% shampoo (Kwell, Scabene), available as a 1% prescription shampoo.

How to use: Apply for 4 minutes to clean, dry hair then add water to lather and rinse, repeat in 7 days.
Reserved for patients who fail to respond to other approved lice therapies due to risk of CNS side effects and associated FDA black box warning.
Resistance is commonly observed.

Ivermectin 0.5% lotion (Sklice) available as a prescription.

Spinosad 0.9% cream rinse (Natroba) available as a prescription.

A newer pediculicide, Spinosad is a fermentation product of the bacterium Saccharopolyspora spinosa that induces muscle spasms and paralysis in lice.
How to use: apply to dry hair, leave on for 10 minutes then rinse, repeat in 7 days.

Topical treatments: Physical mode of action

Benzyl alcohol 5% lotion (Ulesfia) available as a prescription.

Benzyl alcohol is thought to act via asphyxiation by preventing lice from closing their respiratory spiracles, which become blocked by the lotion; it is not ovicidal.
FDA approved for the treatment of head lice in children 6 months of age.
How to use: Two 10-minute applications administered 1 week apart.

Other occlusive agents: Vaseline Petroleum Jelly, mayonnaise, or Cetaphil cleanser

Quite messy and difficult to remove, but it is an inexpensive and sometimes effective method that asphyxiates the lice and nits.
How to use: Apply to entire scalp and is left on under a shower cap overnight, repeat in 7 days.

Oral Pediculicide

Ivermectin via prescription as 3 mg tabs.

How to use: Take 200 to 400 mcg/kg of ivermectin on days 1 and 8.
Ivermectin is an option for patients whose disease is resistant to topical treatments.
Children who weigh less than 33 pounds (15 kg) and pregnant or breastfeeding women should not receive oral ivermectin since safety data on these populations are not available.