Task specific grip force control in writer's cramp.
OBJECTIVE
Writer's cramp is defined as a task specific focal dystonia generating hypertonic muscle co-contractions during handwriting resulting in impaired writing performance and exaggerated finger force. However, little is known about the generalisation of grip force across tasks others than writing. The aim of the study was to directly compare regulation of grip forces during handwriting with force regulation in other fine-motor tasks in patients and control subjects.


METHODS
Handwriting, lifting and cyclic movements of a grasped object were investigated in 21 patients and 14 controls. The applied forces were registered in all three tasks and compared between groups and tasks. In addition, task-specific measures of fine-motor skill were assessed.


RESULTS
As expected, patients generated exaggerated forces during handwriting compared to control subjects. However there were no statistically significant group differences during lifting and cyclic movements. The control group revealed a generalisation of grip forces across manual tasks whereas in patients there was no such correlation.


CONCLUSIONS
We conclude that increased finger forces during handwriting are a task-specific phenomenon that does not necessarily generalise to other fine-motor tasks.


CONCLUSIONS
Force control of patients with writer's cramp in handwriting and other fine-motor tasks is characterised by individualised control strategies.
Schön Klinik München Harlaching, Munich, Germany; Clinical Neuropsychology Research Group (EKN), Clinic of Neuropsychology, Hospital München-Bogenhausen, Germany.
A S
AS
Schneider
Clinical Neuropsychology Research Group (EKN), Clinic of Neuropsychology, Hospital München-Bogenhausen, Germany.
W
W
Fürholzer
Clinical Neuropsychology Research Group (EKN), Clinic of Neuropsychology, Hospital München-Bogenhausen, Germany.
C
C
Marquardt
Department of Sport and Health Science, Technische Universität München, Germany. Electronic address: Joachim.Hermsdoerfer@tum.de.
J
J
Hermsdörfer
D000328:Adult; D020821:Dystonic Disorders / Q000503:physiopathology*; D005260:Female; D005385:Fingers / Q000503:physiopathology; D018737:Hand Strength / Q000502:physiology*; D006236:Handwriting; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D055815:Young Adult
Focal dystonia; Force analysis; Grip force; Handwriting; Writer’s cramp