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.

Predicting Improvement in Writer’s Cramp Symptoms following Botulinum Neurotoxin Injection Therapy

“…15,16 Despite the limitations of these assessments, there remains a tendency in the literature to employ only one scale from multiple categories, 12,17 or apply only one type of assessment. 15,[18][19][20] This lack of comprehensive measurement, which has inhibited the development of a BoNT-A response profile for writer's cramp, may be overcome by implementing various measures from all assessment categories. Therefore, the aim of the present study is to utilize a comprehensive measurement paradigm, implemented at baseline, to create predictive profiles of BoNT-A responders and nonresponders.…”

Predicting Improvement in Writer’s Cramp Symptoms following Botulinum Neurotoxin Injection Therapy

“…Kinematic measurement offers an objective method of assessing movement, but studies of biomechanical analyses to date have generally ignored the multi-segmental nature of the disorder,14 focusing on specific joint angles or applied forces 15,16. Despite the limitations of these assessments, there remains a tendency in the literature to employ only one scale from multiple categories,12,17 or apply only one type of assessment 15,18–20. This lack of comprehensive measurement, which has inhibited the development of a BoNT-A response profile for writer’s cramp, may be overcome by implementing various measures from all assessment categories.…”

“… 15 , 16 Despite the limitations of these assessments, there remains a tendency in the literature to employ only one scale from multiple categories, 12 , 17 or apply only one type of assessment. 15 , 18 – 20 This lack of comprehensive measurement, which has inhibited the development of a BoNT-A response profile for writer’s cramp, may be overcome by implementing various measures from all assessment categories. Therefore, the aim of the present study is to utilize a comprehensive measurement paradigm, implemented at baseline, to create predictive profiles of BoNT-A responders and non-responders.…”