Specific components of manual dexterity are affected in patients with writer's cramp: an observational comparative study and preliminary rehabilitation report.

Abstract

To compare manual dexterity in patients with writer's cramp and healthy controls to determine which components of dexterity are impaired in writer's cramp. In addition, to assess the effects of rehabilitation. Cross-sectional primary study, longitudinal secondary study. 23 patients with writer's cramp and 20 healthy age- and sex-matched control subjects. Degree of manual dexterity (through 3 tasks) and handwriting symptoms were assessed, and effects of rehabilitation probed. Patients with writer's cramp showed significantly lower handwriting speed (97 letters/min) and legibility (BFM score = 1.3) compared with control subjects (171 letters/min, p < 0.001; BFM score = 0.15, p < 0.001). Only the task quantifying finger independence showed weaker finger selectivity (median = 0.84) in patients compared with controls (median = 0.89, p = 0.01). The other 2 tasks, maximal finger tapping and visuomotor finger force-tracking, did not reveal significant group differences (all p > 0.44). In patients, automated writing legibility correlated with finger selectivity (r = 0.50, p = 0.02). Rehabilitation improved dexterity (selectivity and force-tracking) and automated writing legibility. In this multi-component analysis of manual dexterity, reduced selectivity of finger movements was identified as the main behavioural mechanism (deficit) in writer's cramp, associated with writing speed. In contrast, force control and tapping speed were unaffected. Selective finger activation can be improved with therapy targeting dextrous finger movements.