Unilateral Holmes tremor and focal dystonia after Gamma Knife surgery.

Holmes tremor is a rare, involuntary slow shaking in the proximal portions of the limbs during rest and voluntary motion. It occurs frequently after midbrain damage. The authors report on a 20-year-old man who developed Holmes tremor after undergoing Gamma Knife surgery for an arteriovenous malformation in the left thalamus extending to the tegmentum. This is possibly the first report of such an adverse effect after radiosurgery. The tremor was believed to be secondary to radiation-induced infarction of the midbrain.