Publish date: Posted on
Last updated: February 17, 2024
Keywords #
pediculosis capitis
head louse
head lice
Diagnosis #
Pediculosis capitis, commonly known as head lice, is a contagious parasitic infection that affects the human scalp and hair. It is most commonly transmitted via head-to-head contact with an affected person and can rarely spread through infested clothing, combs, towels, or bedding. The head louse has an average life span of 30 days and requires a human host; without the host it dies within 1 to 2 days.[1] The female louse will lay 8 to 10 nits, or eggs, daily near the scalp.[1] Between 7 to 12 days, the nits hatch releasing nymphs that grow in to adult lice.[1] Lice feed every 3 to 4 hours by injecting saliva into the scalp allowing vasodilation and anticoagulation.[1] The saliva leads to an allergic reaction causing a pruritic reaction in the skin.
Key Concepts #
- Pediculosis capitis is a parasitic infection transmitted by head-to-head contact or through infested objects that come into contact with the scalp.
- The saliva triggers a delayed hypersensitivity reaction leading to pruritus.
- Treatments aim to destroy the louse, but repeat treatments are necessary as most treatments cannot penetrate the eggs.[2]
Epidemiology #
Pediculosis capitis is a common parasite that can affect individuals across all age groups and socioeconomic classes with about 6-12 million cases annually.[1]It is most prevalent in younger children (ages 3-12) in daycare, preschool or elementary school. Infestation is more common during the warmer months and primarily affects individuals with longer hair.[3] Incidence is lower in African Americans, which has been attributed to use of hair pomades and lice possibly being better able to grasp more cylindrical hairs of Caucasians or Asian Americans.[3]
Clinical Features #
- Nits (louse eggs) are best seen on the occipital and retroauricular portions of the scalp.
- Adult lice are found attached to hair shafts.
- Pruritus is common but can take 2 to 6 weeks after an initial infestation. Subsequent infestations can lead to pruritus within one to two days.[2]
- Excoriations around present the scalp and neck. The intense scratching can lead to secondary staphylococcal skin infections.[2]
- Cervical lymphadenopathy and conjunctivitis may also be present.
Differential Diagnoses #
- Pseudonits
- Piedra
Diagnostic Workup #
Head lice is definitively diagnosed by finding at least one live louse on visual inspection and is best visualized with a bright light, magnifying lens, and use of fine-tooth comb behind the ears and on the posterior neck.[2] Nits alone are not diagnostic of a current infestation as nits can remain attached for months after a successful treatment and may not still have viable eggs.[2]
Treatment #
All lice infestations should be treated. Topical treatments (pediculicides) are first-line treatments with permethrin 1% lotion being the most common. Apply permethrin lotion to damp hair that has been shampooed (no conditioner) and towel dried. The lotion remains on for 10 minutes before rinsing off.[4] Treatment is repeated around day 9 to kill any nymphs that have emerged from the viable nits.[4]. Permethrin is well-tolerated but can cause scalp pruritus, erythema, and edema and resistance to permethrin has been reported.[4] As head lice cannot live far from the scalp and nits cannot hatch in room temperature excess cleaning of the household or school, like spraying pesticide and powders, is unnecessary.[5] However, items that come into contact with the head including hats, pillowcases, bedsheets, clothes, brushes, and combs are recommended for decontamination. They can be washed in hot water (66°C), dried in a hot dryer for 15 min or stored in an occlusive plastic bag for 2 weeks which will kill the lice and nits.[5]
Slide Viewer #
https://utahderm.med.utah.edu/image-viewer/References #
- Bohl, Brittany, Evetts, Jessica, McClain, Kymberli, Rosenauer, Amanda, and Stellitano, Emily. “Clinical Practice Update: Pediculosis Capitis.” Pediatric Nursing 41.5 (2015): 227.
- Gunning, Karen, PharmD, Pippitt, Karly, MD, Kiraly, Bernadette, MD, and Sayler, Morgan, PharmD. “Pediculosis and Scabies: A Treatment Update.” American Family Physician86.6 (2012): 535-41.
- Ko, Christine J, and Elston, Dirk M. “Pediculosis.” Journal of the American Academy of Dermatology50.1 (2004): 1-12.
- Devore, Cynthia D, and Schutze, Gordon E. “Head Lice.” Pediatrics (Evanston)135.5 (2015): E1355-1365.
- “Head Lice Infestations: A Clinical Update.” Paediatrics & Child Health13.8 (2008): 692-96.
