Writer’s cramp

Writer’s cramp is one of many task-specific dystonias that develops in parts of the body involved in highly skilled, overlearned tasks, like writing, typing, or playing the piano. Prior evidence has demonstrated underlying defects in the basal ganglia including probable dysfunction of the indirect pathway that impairs suppression of unwanted excessive muscle activity surrounding an intended target movement.¹ Nevertheless, a recent editorial in Neurology implicates the cerebellum.² How might cerebellar dysfunction lead to dystonia?

The article by Delmaire et al.³ in this issue of Neurology adds evidence of cerebellar involvement. They used voxel-based morphometry (VBM) of MR images to identify abnormal brain regions in 30 people with right handed writer’s cramp. Gray matter volume in the hand area of the left primary sensorimotor cortex, bilateral posterior thalamus, and cerebellum was reduced, whereas others reported increased volume in sensorimotor cortex and other regions.^4,5 How can one reconcile these differences, especially since one of these other studies had more people with writer’s cramp and used a more a more powerful MR scanner (3T rather than 1.5 T)? Two issues must be considered: methodologic and interpretative. Differences in sensitivity due to scanner types, variations …