11.19 Pediculosis (Lice, crabs)

agk’s Library of Common Simple Emergencies

Presentation

Patients arrive with emotions ranging from annoyance to sheer disgust at the discovery of an infestation with lice or crabs and request acute medical care. There may be extreme pruritis and the patient may bring in a sample of the creature to show you. The adult forms of head lice (pediculosis) can be very difficult to find but their oval, light gray eggs (nits) can be readily found firmly attached to the hairs above the ears and toward the occiput. Secondary impetigo and furunculosis can occur. The adult forms of pubic lice (pthirus or crab lice) are more easily found, but their light yellow gray color still makes them difficult to see. Small black dots present in infested areas represent either ingested blood in adult lice or their excreta.

What to do:

• Instruct the patient and other close contacts on the use of pyrethrins with piperonyl butoxide (RID), an over-the- counter louse remedy which should be applied undiluted to the hair until the affected area is entirely wet. After 10 minutes the infested area should be shampooed and thoroughly rinsed with warm water. This treatment may be repeated if necessary, but it should not be used more than twice within a 24 hr period and it is advisable to wait a week before repeating treatment should reinfestation occur.
• Alternatively, try one application of permethrin 1% cream rinse.
• Families should also be instructed to disinfect sheets and clothing by machine washing in hot water, machine drying on the hot cycle for 20 minutes, ironing, dry cleaning, or storage in plastic bags for two weeks. Combs and brushes should be soaked in 2% Lysol or heated in water to about 65 degrees C for 10 minutes.
• Application of a 1:1 solution of white vinegar and water may help to loosen nits prior to removal with a fine- toothed comb.

What not to do:

• Do not have the family use commercial sprays (R&C; Spray or Li-Ban Spray) to control lice on inanimate objects. Their use is no more effective than vacuuming.
• Do not let patients use lindane (Kwell) shampoo on mucous membranes, around the eyes, on acutely inflamed areas, and do not prescribe it for pregnant women and infants. It is absorbed and can be toxic to the central nervous system.

Discussion

Head and pubic lice are obligatory bloodsucking ectoparasites whose eggs are firmly attached to the hair shafts near the skin, and incubate for about a week before hatching. Nits located more than one-half inch from the scalp are no longer viable.

A common alternate treatment for lice is lindane shampoo which is only available by prescription. One ounce is worked into the affected area for four minutes and then thoroughly rinsed out. Because of the very toxic nature of lindane, its use should be reserved for those cases that fail to respond to pyrethrins (RID). Treatment with either substance may not be ovicidal and therefore re-treatment after 7 to 10 days is often recommended.

Illustration

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