ESSENTIALS OF DIAGNOSIS
Pruritus with excoriation.
Nits on hair shafts; lice on skin or clothes.
Occasionally, sky-blue macules (maculae ceruleae) on the inner thighs or lower abdomen in pubic louse infestation.
Pediculosis is a parasitic infestation of the skin of the scalp, trunk, or pubic areas. Body lice usually occur among people who live in overcrowded dwellings with inadequate hygiene facilities. Pubic lice may be sexually transmitted. Head lice may be transmitted by shared use of hats or combs. Adults in contact with children with head lice frequently acquire the infestation.
There are three different varieties (1) pediculosis capitis, caused by Pediculus humanus var capitis (head louse); (2) pediculosis corporis, caused by Pediculus humanus var corporis (body louse); and (3) pediculosis pubis, caused by Phthirus pubis (pubic louse, “crabs”).
Head and body lice are similar in appearance and are 3–4 mm long. The body louse can seldom be found on the body, because the insect comes onto the skin only to feed and must be looked for in the seams of the clothing. Trench fever, relapsing fever, and typhus are transmitted by the body louse in countries where those diseases are endemic. In the United States, Bartonella quintana, the organism that causes trench fever, has been found in lice infesting the homeless population.
In body louse infestations, itching may be very intense, and scratching may result in deep excoriations, especially over the upper shoulders, posterior flanks, and neck. In some cases, only itching is present, with few excoriations seen. Pyoderma may be the presenting sign. Diagnosis is made by examining the seams of clothing for nits and lice. Head lice presents as scalp pruritus often accompanied by erosions on the occipital scalp, posterior neck, and upper back. Diagnosis is made by finding lice on the scalp or small nits resembling pussy willow buds on the scalp hairs close to the skin (eFigure 6–85). Nits are easiest to see above the ears and at the nape of the neck. Pubic louse infestations are occasionally generalized, particularly in hairy individuals; the lice may even be found on the eyelashes and in the scalp. Diagnosis is made by finding lice or nits on pubic hair, body hair, or eyelashes.
Pediculosis capitis. Upper hair shows nonviable nit (empty with operculum raised); lower hair shows intact, viable, unhatched nit (embryo with eye spot and claws). (From Professor David Taplin and Terri Meinking. Reproduced, with permission, from Curr Concepts Skin Dis. 1989;10:6.)
Head louse infestation must be distinguished from seborrheic dermatitis, body louse infestation from scabies and bedbug bites, and pubic louse infestation from anogenital pruritus and eczema.