Spatial discrimination is abnormal in focal hand dystonia

Background: In patients with focal hand dystonia, abnormal digit representa tions in the primary somatosensory cortex (S1) could be the result of enlar ged and overlapping receptor fields, as suggested by an animal model of dys tonia. A possible clinical correlate of this S1 abnormality is a disturbed spatial discrimination capability. Objective: To test the hypothesis that s omatosensory spatial discrimination is abnormal in focal hand dystonia. Met hods: Seventeen patients with focal hand dystonia underwent a quantitative evaluation of somatosensory spatial frequency (gap detection, JVP domes, ap plied to the distal phalanx of the index finger) and single-touch localizat ion (Von Frey monofilaments, applied to the middle phalanx of the index fin ger). Results: Compared with control subjects, patients had a decreased per formance in both the gap detection (p = 0.004) and the localization (p = 0. 013) tasks. The extent of spatial frequency abnormality correlated with age in both groups. Conclusions: These findings, together with a previously sh own temporal discrimination deficit, support a role for sensory dysfunction in the pathophysiology of dystonia.