Dermoscopic observation of Pthirus pubis

A 52-year-old man presented with a 1-month history of a pruritic trunk rash.Examination revealed pink papules with excoriations and wheals.Dermoscopy of the back serendipitously captured a Pthirus pubis (crab louse) recently exiting its stage III nymph exoskeleton and grasping surrounding hair.Although typically seen on the eyelids or genital hair, a genital examination was not performed, given the finding of multiple adult lice and nits visible on the back.Histology was not required for diagnosis in this case because the dermoscopic findings were definitive.Pthirus pubis undergoes a life cycle beginning with eggs (nits) attached to hair shafts, followed by 3 nymphal stages before reaching adulthood. 1,2The dermoscopic image (Fig 1) captures ecdysis, showing the shedding of the louse's exoskeleton (red arrow) transitioning toward adulthood (black arrow).This dermoscopic finding facilitated rapid and accurate diagnosis, eliminating the need for further testing.