Writer's cramp: literally in your head.

A new study suggests that the hand and arm spasms of chronic writer's cramp are not just psychosomatic symptoms, as some psychologists thought. Instead, this often debilitating disorder may result from abnormal functioning in part of the brain, report two neurologists from Washington University School of Medicine in St. Louis.

Lee W. Tempel and Joel S. Perlmutter used PET scans, which highlight areas of increased blood flow, to gauge brain activity in six people, aged 24 to 72, suffering from writer's cramp in the right hand. They compared these brain scans with those of an age-matched control group of eight people without writer's cramp. The researchers made the PET scans after stimulating the hands of both groups with a vibrator.

On average, the people with writer's cramp showed only two-thirds as much blood flow in the sensorimotor cortex -- the brain region responsible for hand sensation and movement -- compared with controls, Tempel and Perlmutter found.

Although the volunteers with writer's cramp experienced symptoms only in the right hand and arm, their PET scans revealed reduced blood flow in the sensorimotor cortex on both sides of the brain. "This was a surprise," Tempel says, adding that it might explain why writer's cramp sufferers who learn to write with their other hand eventually develop symptoms in that hand as well. Tempell says the results also suggest that writer's cramp is a form of focal dystonia, a brain disorder characterized by involuntary muscle spasms.