Primary writing tremor: motor cortex reorganisation and disinhibition.

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.