Writer's cramp

Writer's cramp or focal hand dystonia (FHD) is an idiopathic movement disorder of adult onset, characterized by abnormal posturing and movement of the hand and/or forearm during tasks requiring skilled hand use, such as writing. Overcontraction of affected muscles, cocontraction of agonist and antagonist pairs, and activation of muscles inappropriate to a task all impair use of the affected hand.

Writer's cramp is a task-specific focal dystonia of the hand. "Focal" refers to the symptoms being limited to one location (the hand in this case), and "task-specific" means that symptoms first occur only when the individual engages in a particular activity. Writer's cramp first affects an individual by interfering with their ability to write, especially for prolonged periods of time.

Epidemiologic studies report a prevalence of 7–69 per million population, or 1 in 15,000–140,000 people, which explains its recognition as a rare disease, like all other forms of dystonia.