11.19 Pediculosis (Lice, crabs)
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agk's Library of Common Simple Emergencies

Presentation
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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:
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- 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:
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- 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
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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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img/cse1119.gif

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 from Buttaravoli & Stair: COMMON SIMPLE EMERGENCIES
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