Value of dermoscopy for the diagnosis of monilethrix.

Monilethrix is a rare genodermatosis characterized by a hair shaft dysplasia responsible for hypotrichosis. We report the case of a child with monilethrix with no associated cases in the family. Trichoscopy facilitated the diagnosis. A 2-year-old boy presented with diffuse alopecia and persistent fragile hair for several months. Clinical examination revealed alopecia with hairs broken several millimeters from the scalp. Trichoscopy revealed zones of dystrophic constriction of the hair shaft, separated at regular intervals by elliptical nodes of normal thickness, giving a "necklace" appearance. The diagnosis of monilethrix was made on the basis of these specific features. The diagnosis of monilethrix was more difficult to establish in our patient owing to the absence of any familial cases.