Harlequin syndrome: An asymmetric face.

Harlequin syndrome corresponds to unilateral dysfunction of the sympathetic system, characterized by flush and unilateral hyperhidrosis associated with hypo or anhidrosis and paleness of the opposite side. It is, usually, idiopathic. Rarely, it may be associated with compressive organic processes, iatrogenic causes, and general diseases. It is a real therapeutic challenge.