Hand cramps: clinical features and electromyographic patterns in a focal dystonia.

We studied 19 patients with hand cramps, including writer's cramp, typist's cramp, piano, and guitar player's cramp. EMGs were recorded while patients performed the task triggering the cramps. Ten patients with dystonic cramps had EMGs with generalized muscle spasms with co-contraction of agonist and antagonist muscles. In three patients with simple cramps that involved one to three fingers, specific muscle groups showed co-contracting bursts that lasted longer than normal. The physiological abnormalities support the interpretation that hand cramp is a focal dystonia, characterized by both excessive muscle activity and defective fine motor control.