Background: Primary writing tremor (PWT) is a task-specific tremor of uncertain origin. There has been debate as to whether PWT represents a variant of essential tremor or a tremulous form of focal dystonia related to writer's cramp. In writer's cramp there is evidence of changes in intracortical inhibition (ICI), as well as cortical motor reorganisation.
Objective: To study corticomotor organisation and short-latency ICI in a patient with typical task-specific PWT.
Methods: Transcranial magnetic stimulation mapping of the corticomotor representation of the hand and studies of ICI using paired-pulse stimulation were performed in a 47-year-old right-handed woman with a pure task-specific writing tremor.
Results: The motor maps for the hand were displaced posteriorly on both sides and reverted to a normal position after treatment with botulinum toxin. Short-latency ICI was reduced for the dominant hand.
Conclusion: The findings indicate reorganisation and disinhibition of the corticomotor projection to the hand and point to the participation of cortical centres in the origin of PWT.