Brain, Vol. 125, No. 4, 895-903,
April 2002
© 2002 Guarantors of Brain
Abnormal cortical mechanisms of voluntary muscle relaxation in patients with writer’s cramp: an fMRI study
1 Departments of Brain Pathophysiology, Human Brain Research Center, 2 Neurology and 3 Nuclear Medicine, Kyoto University Graduate School of Medicine, Kyoto, 4 Laboratory of Cerebral Integration, National Institute for Physiological Sciences, Myodaiji, Okazaki, and 5 Department of Neurology, Tokushima University School of Medicine, Tokushima, Japan
Correspondence to: Hiroshi Shibasaki, MD, PhD, Department of Brain Pathophysiology, Human Brain Research Center, Kyoto University Graduate School of Medicine, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606–8507 Japan E-mail; shib{at}kuhp.kyoto-u.ac.jp
Although it is hypothesized that there is abnormal motor inhibition in patients with dystonia, the question remains as to whether the mechanism related to motor inhibition is specifically impaired. The objective of the present study was to clarify the possible abnormalities of the mechanisms underlying voluntary muscle relaxation during motor preparation and execution in patients with writer’s cramp, using event-related functional MRI. Eight patients with writer’s cramp and 12 age-matched control subjects participated in the study. Two motor tasks were employed as an experimental paradigm. In the relaxation task, subjects were asked to hold their right wrist in the horizontal plane by maintaining moderate contraction of wrist extensor muscles in the premotor phase; they relaxed those muscles voluntarily just once during each fMRI scanning session. In the contraction task, subjects extended the right wrist voluntarily from the same premotor state as for the relaxation task. Five axial images covering the primary sensorimotor cortex (SMC) and supplementary motor area (SMA) were obtained once every second. Activated volumes in the left SMC and the SMA were significantly reduced in patients for both muscle relaxation and contraction tasks. These data suggest that there is impaired activation in both SMC and SMA in voluntary muscle relaxation and contraction in patients with writer’s cramp. This implies that abnormalities of both inhibitory and excitatory mechanisms in motor cortices might play a role in the pathophysiology of focal dystonia.
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