Synonyms: focal hand dystonia, task-specific dystonia of writing, writing dystonia
Dystonia is an involuntary, sustained muscle contraction with abnormal postures. Focal dystonia affects only one body part. Writer's cramp is a type of focal dystonia that is specific to the task of writing and is the most common focal primary dystonic disorder. Typically it begins with an abnormally tight grip while writing, progressing to increasing difficulty with the task. Excessive muscle spasms may progress proximally, leading to abduction of the arm. Although historically thought to be psychogenic, it is now recognised as a type of dystonia, and consists of both a sensory impairment with reduced spatial sensitivity, and a motor abnormality.1Functional MRI suggests that there is a defect in inhibitory control that may explain the unintended activation of muscles and resulting abnormal movements. Cerebellar abnormalities have been detected, as well as abnormal dopaminergic transmission in the basal ganglia, but it is not understood whether these are the cause or the effect of writer's cramp.2The main pathophysiological mechanisms explaining the disorganisation of the sensory-motor system appear to be loss of inhibition, aberrant neural plasticity, and defective learning-based sensory-motor integration.3
This is a companion discussion topic for the original article at https://patient.info/doctor/neurology/writers-cramp