Poliosis circumscripta: overview and underlying causes.

Although traditionally known as "white forelock," poliosis circumscripta, defined as a localized patch of white hair in a group of hair follicles, can involve any hairy area on the body including the scalp, eyebrows, and eyelashes. Microscopically, poliosis demonstrates either decreased or absent melanin and/or melanocytes in the hair bulbs of the affected hair follicles. Classically, poliosis is known to occur in the setting of several genetic syndromes including piebaldism, Waardenburg, and tuberous sclerosis. In addition, poliosis has been described in association with various acquired conditions. These include inflammatory conditions, benign and malignant neoplastic entities that are mainly melanocytic, medications, and others. In this review, we aim to describe the different conditions where poliosis may be encountered, with the aim of helping the clinician to better evaluate any patient presenting with poliosis.