cqvip:Background: Focal task specific dystonia occurs preferentially during perform ance of a specific task. There may be an inefficiently high grip force when doin g manipulative tasks other than the trigger task, possibly reflecting a generali sed impairment of sensory- motor integration. Objective: To examine how well su bjects with writer’ s cramp (n=4) or musician’ s cramp (n=5) adapted their gri p force when lifting a new object or catching a weight. Methods: Nine patients with focal hand dystonia and 10 controls were studied. Experiments addressed different motor behaviours: (A) lifting and holding an ob ject; (B) adjusting grip force in anticipation of or in reaction to a change in load force by catching a small weight dropped expectedly or unexpectedly into a hand held receptacle. Results: In (A), patients produced a grip force overshoot during the initial lifts; force overflow was most pronounced in those with write r’ s cramp. Patients and controls adjusted their grip force to object weight wi thin one or two lifts, though patients settled to a steady force level above nor mal. In (B), patients with focal hand dystonia and normal controls showed simila r predictive grip force adjustments to expected changes in object load, suggesti ng that this aspect of sensory- motor integration was normal. Patients had a sh orter latency of grip force response than controls after an unexpected load incr ease, reflecting either a greater level of preparatory motor activity or a disin hibited spinal reflex response. Conclusions: The overall increased grip force in patients with focal hand dystonia is likely to be a prelearned phenomenon rathe r than a primary disorder of sensory- motor integration.
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