Chewing-induced facial dystonia.

Dear Editor, Dystonia is a movement disorder characterised by sustained muscle contractions, repetitive twisting movements, and abnormal postures of the trunk, neck, face, or arms and legs.1 Classifi cation of this condition may be based on topography, age at onset, cause, or by the presence of genetic markers.1 When unaccompanied by other neurologic abnormalities, and in the absence of known causes (except some genetic mutations), the dystonia is said to be “primary”. Focal dystonia is that which affects a single region, e.g. cervical dystonia, blepharospasm or laryngeal dystonia. Dystonia may also be classifi ed according to phenomenology. Hence, abnormal posturing that occurs during voluntary activity is called “action dystonia”, the eponym “task-specifi c” being appended when action dystonia is triggered by specifi c actions.1