title: Botulinum neurotoxin treatment improves force regulation in writer's cramp.
abstract: Writer's cramp patients show poor force regulation during handwriting, but also in other experimental tasks requiring fine motor control. Botulinum neurotoxin (BoNT) treatment is clinically effective in a substantial portion of writer's cramp patients, but the full mechanism of action remains enigmatic. BoNT possibly influences α- and γ-motoneurons through chemodenervation not only of extra-, but also intrafusal muscle fibres and might thus influence muscle spindle afferents. Hence, BoNT weakens injected muscles, but may also modulate sensory aspects of force control. Ten patients and 18 controls pressed their index finger on a force sensor tracking two visual targets: The first target consisted of five plateaus with successively higher force levels and alternated with ascending ramps. In the second target condition the same successive plateaus were to be reached by abrupt jumps. The generated force displayed as a time dependant curve. Root mean square of the difference between target and produced force level was calculated for each plateau/ramp/jump. Patients were treated with BoNT at week 4 and measured at baseline, weeks 2, 4, 6 and 8. Disturbed force regulation in patients for the plateaus and the second jump at baseline resolved after BoNT treatment, and the root mean square of force deviation decreased for the ramps. Fine force control was within the 95% confidence interval of the control group after treatment. In conclusion, force regulation was disturbed in patients and improved after BoNT treatment. This is not compatible with a simple muscle weakening and might thus reflect improved sensorimotor integration.
authors.affiliation: Department of Neurology, Kiel University, Neurozentrum, Arnold Heller Strasse 3, Haus 41, 24105 Kiel, Germany. k.zeuner@neurologie.uni-kiel.de
authors.forename: Kirsten E
authors.initials: KE
authors.lastname: Zeuner
authors.forename: Arne
authors.initials: A
authors.lastname: Knutzen
authors.forename: Lucas
authors.initials: L
authors.lastname: Pedack
authors.forename: Mark
authors.initials: M
authors.lastname: Hallett
authors.forename: Günther
authors.initials: G
authors.lastname: Deuschl
authors.forename: Jens
authors.initials: J
authors.lastname: Volkmann
mesh_terms: D000328:Adult; D000368:Aged; D018726:Anti-Dyskinesia Agents / Q000494:pharmacology / Q000627:therapeutic use*; D001905:Botulinum Toxins / Q000494:pharmacology / Q000627:therapeutic use*; D016022:Case-Control Studies; D004185:Disability Evaluation; D020821:Dystonic Disorders / Q000188:drug therapy* / Q000503:physiopathology*; D005260:Female; D005385:Fingers / Q000294:innervation; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011597:Psychomotor Performance / Q000187:drug effects*; D012720:Severity of Illness Index; D018709:Statistics, Nonparametric; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D018726:Anti-Dyskinesia Agents; D001905:Botulinum Toxins