Clinical presentation
A 62-year-old man presented to our department because of pubic pruritus for 1 week, claiming it started after wearing a new pair of briefs. Cutaneous examination found small, yellowish-brown moving flecks attached to the hair in the pubic region (Fig 1).
Fig 1.
Pediculosis pubis. Both adult crab lice and nits are visible to naked eye.
Dermoscopic appearance
Dermoscopic examination found 3 stages of Pthirus pubis, namely nits or eggs, nymph, and adult stages.1 The brown or white eggs or nits containing nymphs were firmly attached at the base of a hair. Nymphs are essentially a smaller version of adults, making them very difficult to find. Adults were seen grasping hairs with claws or sucking the blood by inserting mouth parts into the skin (Fig 2). Detailed dermoscopy found live and moving lice.
Fig 2.
Pediculosis pubis. Dermoscopy observation. A, Nits (white arrows), nymphs (black arrow), and adults (red arrow) within a single field of view. B, An adult louse grasping hairs with claws. C, Adults sucking the blood by inserting mouth parts into the skin.
Direct microscopy of Phthirus pubis
Direct microscopy found an adult Pthirus pubis. An adult Pthirus pubis can be identified by a series of features. It is about 1.5 to 2 mm long, slightly smaller than the body louse and head louse, and can be distinguished from those other species by its almost round body. Another distinguishing feature is that the posterior 2 pairs of legs of a crab louse are much thicker than the front legs and have large claws much like the pincers of a crab—hence the nickname (Fig 3).
Key message.
Pediculosis pubis is caused by the louse, Pthirus pubis. Pubic pruritus is the cardinal symptom. Diagnosis is based on the detection of lice or nits, which are difficult but possible to see with close inspection or magnification. Dermoscopy could enable a rapid and efficient diagnosis without the need of a microscope or other more sophisticated devices. Dermoscopy is also a technique that aids in follow-up examinations.
Fig 3.
Pediculosis pubis. Direct microscopy found an adult Pthirus pubis. (Original magnification: ×40.)
Footnotes
Funding sources: National Natural Science Foundation of China (Grant No. 81502719).
Conflicts of interest: None declared.
Reference
- 1.Tang J.Q., Ran X., Ran Y.P. Cover Image: Dermoscopy in vivo for the life cycle of Phthirus pubis. Br J Dermatol. 2017;176:279. doi: 10.1111/bjd.15049. [DOI] [PubMed] [Google Scholar]