Deficient activation of the motor cortical network in patients with writer's cramp

Objective: To study regional cerebral blood flow (rCBF) in patients with si mple writer's cramp using PET to identify regions that malfunction. Backgro und: Several lines of evidence indicate impaired cortical function in patie nts with focal dystonia, but the precise pathophysiology is still unknown, Methods: Seven patients with writer's cramp were compared with seven age- a nd sex-matched control subjects. Control subjects and patients were scanned during sustained contraction, tapping, and writing with the right hand. Af ter realignment and stereotactic normalization of the scans, all tasks were compared with a rest condition. For each task, an intra- and intergroup co mparison was performed using statistical parametric mapping. For each condi tion and within groups, rCBF correlation analysis was performed between som e selected regions that were activated during movement. Results: In control subjects and patients, significant increases of rCBF were observed for eac h task in areas already known to be activated in motor paradigms. The inter group comparison disclosed less activation in writer's cramp patients for s everal areas for all three tasks. This decrease reached significance for th e sensorimotor cortex during the sustained contraction task and for the pre motor cortex during writing. rCBF correlation analysis showed different pat terns between control subjects and patients. At rest and during writing, th e correlations between the putamen and premotor cortical regions and betwee n the premotor cortical regions themselves mere stronger in control subject s. Conclusions: Deficient activation of premotor cortex and decreased corre lation between premotor cortical regions and putamen suggest a dysfunction of the premotor cortical network in patients with writer's cramp possibly a rising in the basal ganglia. The dysfunction is compatible with a loss of i nhibition during the generation of motor commands, which in turn could be r esponsible for the dystonic movements.