Abstract & Commentary
Source: Zeuner KE, et al. Sensory training for patients with focal hand dystonia. Ann Neurol. 2002;51:593-598.
Focal task-specific dystonia (FTSD) is one of the most unusual movement disorders. Far from rare, it affects a sizable portion of the adult population, typically taking the form of writer’s cramp. By definition FTSD affects only one part of the body (typically the hand), and is triggered only by one specific activity. The task that triggers dystonic symptoms is usually a skilled motor activity requiring sustained attention, such as writing or playing a musical instrument. Aside from dystonia, the neurologic examination is entirely normal, and imaging studies and nerve conduction tests are normal as well.
Over the last decade, numerous studies have demonstrated disordered cortical topography of the hand area in the motor and sensory cortex in patients with FTSD. The normal rigid separation and strict ordering of the fingers in the homunculus is blurred in patients with FTSD. Along with their dystonic symptoms, patients have a deficit in fine sensory perception, which can be demonstrated with a simple technique designed to test the limits of 2-point discrimination.
In the present study, Zeuner and colleagues studied 10 patients with FTSD of the hand and 10 normal controls. They measured sensory perception in the affected hand using the JVP dome system, a series of plastic domes with gratings of different widths cut into their surface. The domes are placed gently against the skin, and the patient is asked to report the orientation of the grooves. The severity of dystonia was evaluated using standard clinical rating scales and by measuring the time needed to write a standard paragraph.
All patients were trained to learn to read Braille for 8 weeks, practicing 1 h/d for the first week and 30 minutes /d for the remaining 7 weeks. Patients practiced at home, and their compliance with the training program was measured by a series of test exercises. Patients practiced using the finger most affected by dystonic contractions. After 8 weeks of training, sensory perception of both patients and controls improved, and the change was statistically significant. Observer’s ratings of the severity of dystonia improved in 5 of 10 patients, and 6 patients shortened the time needed to write a standard paragraph. There was, however, no statistically significant improvement in patients’ rating of their disability. Several patients stopped practicing their Braille reading, only to see their symptoms of dystonia worsen. When they resumed practicing, dystonic symptoms improved.
This is an interesting and important study. Zeuner et al showed that daily practice of an attended, complex motor task (learning to read Braille) alters the sensory perception threshold of both normal and dystonic individuals. Further, learning to read Braille improved rating scale measures of dystonia, although patients did not feel that their functional disability improved. This study provides further evidence that the adult brain possesses remarkable plasticity when presented with a complex task requiring concentrated attention. It also suggests an avenue of further research for therapeutic trials in patients with focal and generalized dystonia. —Steven Frucht
Dr. Frucht, Assistant Professor of Neurology, Movement Disorders Division, Columbia-Presbyterian Medical Center, is Assistant Editor of Neurology Alert.