Pediculosis capitis - External and Internal Eye
The head louse is an obligate human parasite that lives exclusively on scalp hair. Transmission occurs mostly via direct head-to-head contact. The head louse can survive up to 4 days on fomites such as brushes, barrettes, and headgear; therefore, indirect transmission is possible. In one study, live lice were found on the pillowcases of 4% of infested study volunteers.
School-aged children, particularly girls, have the highest incidence, but head lice are present worldwide and affect all socioeconomic classes. All races and ethnicities are affected, with the exception of those with coarse, curly hair that lice are not able to properly attach to.
Outbreaks may occur in settings where there is close contact and/or frequent sharing of hair accessories, such as schools, day care centers, and nursing homes.
Worldwide incidence of pediculosis appears to be on the rise, most likely due to growing resistance to therapy.
Eyelash, eyebrow, and beard areas may rarely be involved; pubic lice are more commonly found on the eyelid area.
B85.0 – Pediculosis due to Pediculus humanus capitis
81000006 – Pediculosis capitis
Differential Diagnosis & Pitfalls
- Infestation of the beard, eyebrows, and/or eyelashes is consistent with crab lice. Crab lice (pediculosis pubis) may infest the hairs of the eyebrows, eyelashes, scalp, axilla, chest, thighs, and perianal area in addition to the pubic area.
- The scales of seborrheic dermatitis may be mistaken for pediculosis capitis; however, these scales are greasy, yellow, irregular in shape, and easily removable, unlike the scales of pediculosis capitis, which adhere to the hair shaft.
- white piedra may be mistaken for nits. and
- Traction alopecia, many inflammatory conditions affecting the scalp (eg, seborrheic dermatitis, psoriasis, folliculitis decalvans, pemphigus vulgaris), and dried hair products (eg, dry shampoos, hair gels) can produce white or yellow concentrations along the hair shaft. These hair casts are often mistaken for nits. Hair casts fully circumscribe the hair shaft and are freely mobile along the hair shaft.
- Tinea capitis has similar pruritus and lymphadenopathy but is associated with alopecia. Nits are not found on close examination of the hair.
- Inflammatory scalp conditions such as psoriasis, lichen planopilaris, and folliculitis all cause pruritic scalp but are morphologically distinctive skin disorders.