The worried mother of a healthy 21-month-old girl asks you to evaluate a peculiar, squiggly blue line on the top of her daughter's right foot.
Diagnosis: Cutaneous pili migrans
Cutaneous pili migrans, also called embedded hair or creeping hair, is a rare skin condition in which an exogenous hair shaft penetrates the superficial skin and burrows itself under the epidermis.1 It typically presents as a linear to curvilinear erythematous tract that may be elevated or flat. It may be asymptomatic, pruritic, or painful.1-5
Careful examination of the top of the patient's right foot revealed a 3-cm, serpiginous, blue, nylon-thread–like structure within the skin without overlying skin changes. The overlying skin was anesthetized with 20% topical lidocaine ointment for 1 hour. After the area was cleaned with an alcohol wipe, a 1-mm incision was made, and a needle and fine-tipped forceps were used to tease the strand from the skin.
Four pediatric cases, all of which have been on the soles of the feet, have been reported out of the 21 total cases reported worldwide to date.4 Our patient is the first case involving the dorsum of the foot.
The etiology here may be that the exogenous hair shaft migrated along the burrow as a result of repetitive friction and trauma while the baby was walking or running.