Dermoscopy of Pubic Louse

A 23-year-old unmarried man presented with itching in the inguino-pubic region of 3 weeks duration, which had started a week after a heterosexual protected sexual contact with a commercial sex worker. Examination revealed excoriation marks in the pubic region and no suggestion of tinea, scabies, or contact allergic dermatitis. Polarized videodermoscopy revealed “crab”-like pubic louse with a broad body and six legs bearing thick claws grasping pubic hairs [Figure 1a]. Dermoscopy of a plucked pubic hair displayed a brown-colored viable nit with an operculum at one end [Figure 1b]. Dermoscopy of a plucked pubic hair demonstrated a nit with a viable nymph. Examination of eyelashes, scalp, and other parts was normal. Serology for human immunodeficiency virus and venereal disease research laboratory tests was negative. Treatment of the patient with two regional applications of 0.5% ivermectin lotion (10 days apart) and hot-wash and hot dryer treatment of fomites was curative.

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Figure 1

(a) Dermoscopy of the pubic region of the patient revealing a “miniature crab”-like light grey-brown colored pubic louse with six legs and the pubic hairs firmly grasped in its claws over the forelegs (Escope, videodermoscope, ×10, polarized). (b) Dermoscopy of a plucked pubic hair displaying a brown-colored viable nit with an operculum at one end (red arrow) (Escope, videodermoscope, ×10, polarized)

Pubic louse or Phthirus pubis is typically acquired through sexual contact, although fomite-borne transmission is possible. Phthirus pubis preferably colonizes apocrine gland-rich regions such as pubic area and axillae. It can affect other hairy regions such as eyelashes (phthiriasis palpebrarum), eyebrows, thigh, beard, chest, and legs.[1] Unlike head and body lice, pubic lice are smaller (1.2 × 0.8 mm), lighter in color, and less mobile.[2] Pubic lice feed and reproduce on the human host and their nits (that hatch in 8–10 days) are deposited over the hair shaft approximately 1 cm from the skin surface.[1] Their smaller size and less mobility render naked eye detection difficult. Appreciation of macula cerulae is difficult in dark-skinned individuals. Dermoscopy aids in not only quickly diagnosing pediculosis but also facilitates species detection.[2] In contrast to the “miniature crab” appearance of the pubic louse, the adult head louse (Pediculus humanus var. capitis) is larger in size (2–4 mm long), darker in color (tan to grayish-brown), bears six clawed legs [Figure 2a], and displays faster mobility. The female is larger and bears posterior protrusions forming an invaginated “V” structure, whereas male has dark brown bands across its back. Pediculus humanus var. corporis (body louse) is morphologically almost identical to the head louse. Adequacy of pediculocidal treatment and need for retreatment is aided by dermoscopic examination of the plucked hairs to identify nits with vital nymphs and hatched empty cases. Except for the attachment site of the nits (base of the hair in head and pubic lice versus fabric seams in body louse), there is no documented difference in the morphology of nits of the three types of lice. Nits may be confused with pseudonits that are white, bizarrely shaped amorphous non-adherent structures [Figure 2b] that represent hair casts or peripilar keratin casts, typically encountered in scalp psoriasis and seborrheic dermatitis of the scalp.[3]

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Figure 2

(a) Dermoscopic appearance of male head louse. Appreciate its larger size and darker color (dark tan to grayish-brown) compared with pubic louse observed in Figure 1a (Escope, videodermoscope, ×10, polarized). (b) Dermoscopic appearance of a pseudonit (yellow arrow). A white, bizarrely shaped amorphous structure, representing a dandruff flake over the hair shaft of a patient with seborrheic dermatitis of the scalp (Escope, videodermoscope, ×10, polarized)

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