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 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.