A woman presents with adherent scale bound around tufts of her hair. What is the cause?
Over a six-month period, a 23-year-old woman noted on the crown of her scalp the development of adherent scale that bound tufts of hair in an asbestos-like sheath. A scalp biopsy showed a papillomatous surface with hyperkeratinisation that wrapped around hair shafts. The underlying dermis showed superficial lymphocytic inflammation. Stains for fungi were negative.