Characterization of Manual Dexterity by Finger Force Manipuladum (FFM) in Patients With Writer's Cramp and in Control Subjects

Writer's cramp is a focal dystonia characterized by abnormal movements and postures during writing. Limited finger independence during writing manifests as difficulty suppressing unwanted activations of neighbouring non task-relevant fingers. Patients with Writer's cramp also have difficulty in fine control of grip force.

The investigators have recently developed the Finger Force Manipulandum which quantifies the forces applied by each fingers in different tasks. This method is sensitive for detection and quantification of small unwanted contractions in non-active ('stationary') fingers. Different tasks have been developed to assess abilities such as finger individuation but also fine finger force control, finger movement regularity and speed.

The aim of this study is to assess if developed tasks allow to precisely characterize writer's cramp condition in terms of abilities aforementioned.

To do so, performance of 20 writer's cramp patients in the developed task will be compared with performance of 20 control participants (matched in age, sex and writing hand) in the same tasks.