Extragenital Phthiriasis: Diagnosis Made Simple by Dermoscopy.

Abstract

A 21-year-old, otherwise healthy, man presented with a 2-week history of black spots on his lower extremities and buttocks associated with pruritus. On clinical examination, black structures within dense hairs and bilateral inguinal lymphadenopathy were present. Handheld dermoscopy (magnification ×10, Dermlite D4; 3Gen, Juan Capistrano, CA) showed multiple living crab-shaped organisms, consistent with Phthirus pubis, as well as nits attached to the hair shafts; neither could be clearly identified by the naked eye only (Figs. 1, 2; Video 1 [https://links.lww.com/OLQ/A659]). No insects were present in previously shaved genital area. The screening for other sexually transmitted diseases was negative. The patient was successfully treated with 5% topical permethrin and hair removal.Figure 1: Phthirus pubis. aAdult parasite grasping hairs with claws, visible blood within the digestive system. bAdult parasite sucking blood with mouth inserted into the skin.Figure 2: Phthirus pubis. aAdult parasite. bNit. cMacula cerulea.A study by Truesdale et al.1 reported that weighted percentages of pubic hair grooming in women and men in the United States equal 85.3% and 66.5%, respectively. Because of increased pubic hair removal, extragenital P. pubis infestation in hair-bearing areas such as eyebrows, eyelashes, mustache, beard, axillae, and trunk may be more commonly observed.2,3 Because P. pubis is smaller, lighter, nearly transparent, and not as mobile as other lice, the diagnosis of human phthiriasis by the naked eye only may be more difficult.4 There are a few reports on the usability of dermoscopy (entomodermoscopy) in diagnosing of human pthiriasis. This method may be performed both ex vivo and in vivo.2 To our knowledge, this is the first description of the usability of dermoscopy in vivo in extragenital pthiriasis of the lower legs and buttocks. Dermoscopy in vivo enables visualization of the life cycle of P. pubis with empty nits (with flattened ends), nits containing nymphs (brown and ovoid), nymphs, and adult organisms.5 Handheld dermoscopy is a simple and quick method in diagnosing extragenital phthiriasis.