Abnormalities of spatial and temporal sensory discrimination in writer's cramp.

Clinical observations of patients with writer's cramp suggest that abnormalities of the sensory system may be a frequent finding in this disorder. Neurophysiological data from an animal model of focal dystonia have revealed cells in somatosensory cortex with enlarged and overlapping tactile receptive fields. However, psychophysical studies so far have been unable to document a clinical correlate supporting a similar enlargement of receptive fields in humans. We compared the fingertip discrimination of the orientation of fine spatial gratings between writer's cramp and control subjects and found a significant decrease in grating sensitivity in the patients, consistent with the possibility of enlarged tactile receptive fields. In addition, we duplicated previous experiments showing an abnormality of tactile temporal discrimination. The results provide psychophysical measures which may relate to the development of sensory cortical reorganization in patients with writer's cramp.