Pediculosis capitis is an infestation of the scalp by the head louse, which feeds on the human scalp and neck and deposits its eggs on the hair.
SYNONYMS Head lice, louse, nit.
AGE Children > adults.
GENDER F > M.
PREVALENCE 12 million school children annually in the United States. Ten percent of children worldwide.
INCIDENCE Common.
RACE Caucasian, Asians > blacks.
EPIDEMICS In schools.
SEASON Year-round, but greatest in summer.
ETIOLOGY Pediculus humanus capitis (2-mm, six-legged, wingless insect; Fig. 25-1).
Head lice are transmitted from person to person via shared hats, caps, brushes, combs, or head-to-head contact. The Pediculus humanus capitis female lays approximately 10 ova per day gluing its eggs to the hair within 1 to 2 mm of the scalp. The ova hatch in 10 days, the louse emerges as a nymph, reaches its adult form 10 days later, and has a life span of 30 days. Lice have anterior mouthparts that attach and feed on blood five times a day. Lice cannot survive for more than 3 days off the human head. Majority of patients have a population of fewer than 10 head lice.
Humans contract lice by sharing brushes, hats, close head-to-head contact, etc. The scalp louse deposits nits on the hair next to the scalp, and scalp hair grows 0.5 mm daily (thus, the presence of nits 15 cm from the scalp indicates an infestation that is approximately 9 months old). New viable eggs have a creamy-yellow color; empty eggshells are white. The infestation first manifests as severe pruritus of the back and sides of scalp. Crusts and secondarily impetiginized lesions are common and may extend onto the neck, forehead, face, and ears. In extreme cases, the scalp can become a mass of matted hair, lice, nits, and purulent discharge called plica polonica.
TYPE Lice, nits (1-mm eggs; Fig. 25-2), macules, papules, excoriations.
SITES OF PREDILECTION Scalp: occipital, postauricular regions.
ASSOCIATED FINDINGS Cervical or posterior auricular lymphadenopathy may be present.
The differential diagnosis of pediculosis capitis includes hair casts, dried hairspray or gel, dandruff (epidermal scales), impetigo, seborrheic dermatitis, and tinea capitis.
DERMATOPATHOLOGY Bite site will show intradermal hemorrhage and a deep, wedge-shaped infiltrate with eosinophils and lymphocytes.
MICROSCOPIC EXAMINATION Shows lice and/or nits adherent to hair.
WOOD’S LIGHT Nits will fluoresce pearly white-blue and are not movable.
Head lice are best treated with pediculicides: permethrin, lindane, malathion, or mercuric oxide ointment. The pyrethroids are neurotoxic to lice and current management recommends topical 1% or 5% permethrin applied to scalp and washed off after 10 minutes followed by combing nits out with a fine-toothed comb. The treatment should be repeated 8 to 10 days later. If nits and eggs are still present, pyrethrin/pyrethroid-resistant lice may be present and two applications of 0.5% or 1% malathion should be used combined with fine-toothed combing. Other topical agents that may be first-line treatments for head lice include topical spinosad, topical ivermectin, and topical 5% benzyl alcohol.
Lindane should be avoided in children, because there is potential CNS toxicity associated with overuse or accidental ingestion. Home remedies (such as oils, kerosene, formic acid, and vinegar) are also NOT recommended. All other family members should be checked for asymptomatic lice, because epidemics start in the family, not at school. Floors, play areas, and furniture should be vacuumed. Clothes and bedding should be washed and dried on high heat. Combs and brushes should be soaked in pediculicide for 15 minutes and should not be shared between family members until infection is cleared.
Pediculosis pubis is an infestation of hairy regions, most commonly the pubic area but at times the hairy parts of the chest, axillae, and upper eyelashes. It is manifested clinically by mild-to-moderate pruritus.
SYNONYMS Crabs, crab lice, pubic lice, phthiriasis.
AGE 14 to 40 years; most commonly sexually active teenagers and young adults.
GENDER M > F.
INCIDENCE Common.
ETIOLOGY Phthirus pubis (1-mm, six-legged insect, crablike in appearance; Fig. 25-3).
The pubic louse lives exclusively on humans and they are transmitted by close physical contact (crowded living conditions, sharing a bed, sharing towels, sexually transmitted). The P. pubis female lays 1 to 2 ova per day, has a lifecycle of 35 days and cannot live off the human host for more than 1 day. They remain stationary with their embedded mouth parts in the skin and their claws grasping a coarse hair (pubic, perianal, axillary, eyelashes, eyebrows, facial hair) on either side (Fig. 25-4).
Pediculosis pubis may be asymptomatic or pruritic for months. With excoriation, the lesions may become tender with enlarged regional (inguinal, axillary) lymph nodes. There may also be maculae caeruleae (tâches bleues)—slate-gray, 1-cm macules on the trunk or legs— because of the breakdown product of heme from the louse saliva.
TYPE Lice, eggs (nits), macules, papules, excoriation, crust.
COLOR Red, blue (maculae caeruleae).
DISTRIBUTION Pubic, axillary areas > trunk. Children: eyelashes, eyebrows.
Local lymphadenopathy may be present.
The differential diagnosis for pediculosis pubis includes tinea, folliculitis, and scabies.
DERMATOPATHOLOGY Bite site will show intradermal hemorrhage and a deep, wedge-shaped infiltrate with eosinophils and lymphocytes. The lice themselves do not enter into the skin surface.
MICROSCOPY Lice and nits may be identified with hand lens or microscope.
Pubic lice is best treated with topical pediculicides; permethrin, lindane, or malathion are acceptable treatments. The treatment of choice for pubic lice recommended by the CDC is topical permethrin 1% cream applied for 10 minutes and then washed off. Treatment applied once again 7 to 10 days later may demonstrate the best efficacy. If nits and eggs are still present, resistant lice may be present and 0.5% or 1% malathion should be used. Lindane should be avoided in children, because there is potential CNS toxicity associated with overuse or accidental ingestion.
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