Disturbed sensorimotor processing during control of precision grip in patients with writer's cramp

The aim of the study was to investigate force regulation in patients with w riter's cramp when performing a drawer-opening task using the precision gri p. Experimental conditions included intervening load pulses and vibratory m anipulations for examining grip Force responses to sensory disturbances. Th e data revealed that grip force was increased in patients with wr iter's cr amp compared with normal subjects, with a stronger modulation in the sympto matic compared with the asymptomatic hand. This denotes a change in force s caling capabilities and most notably for the preferred hand used in manipul ative activities. Vibratory stimulation of the extrinsic hand/finger muscle s resulted in an increased grip force of both hands in the patients with wr iter's cramp. The latter was not observed in normal subjects and supports a bilateral dysfunction in sensorimotor integration resulting from focal dys tonia. In conclusion, the disturbed regulation of the precision grip during a drawer-opening task is illustrative for the inability of patients with w riter's cramp to efficiently control the force output during manipulative a ctivities.