Objective: To perform a computerised analysis of finger tapping in patients with dystonia and healthy controls in order to develop a better understanding of the dynamics of repetitive actions in dystonia.

Background: The electromyographic features of dystonia—abnormally long EMG bursts, agonist-antagonist co-contraction, overflow activity in remote muscles—are well recognised. Kinematic studies reveal slower, less precise and more variable movements.(1) Analysis of bradykinesia in dystonia has revealed no decremental tendency.(2) However, a detailed exploration of its characteristics has not yet been performed. 

Methods: 30 patients with cervical and/or limb dystonia and 23 healthy controls were compared. A simple task involving repetitive finger tapping was assessed while subjects wore electromagnetic sensors secured to index finger and thumb. Subjects were advised to tap “as fast and as big as possible” for two trials, each 15 seconds long. Precise position and orientation data, in six degrees of freedom, were recorded from each sensor. A high sampling rate permitted ‘real time’ analysis of movement. Separable components (such as rhythm, speed and amplitude) were derived from a comparison of the x, y and z coordinates of each sensor. These components were extracted from the data using a custom script written in MATLAB (The MathWorks Inc., Natick, Massachusetts, USA). Data was then analysed for statistical significance by Mann-Whitney U test using Matlab statistical toolbox software.

Results: The following parameters were significantly different between the groups: in the dystonia group frequency (p = 0.001), maximum opening deceleration (p = 0.0004) and maximum closing acceleration (p = 0.04) were reduced, halt duration was increased (p = 0.01) and the product of amplitude and frequency (a marker of superior overall performance) was lower (p = 0.001). 

Conclusions: There is a loss of efficiency of repetitive actions in dystonia. Extrapyramidal disturbance in dystonia generates slowness of voluntary movement, in addition to the involuntary movement disorder. Improved knowledge of the specific components of bradykinesia in dystonia will aid diagnosis and enhance understanding of its underlying mechanisms.

References:

1. Berardelli A, Rothwell JC, Hallett M, Thompson PD, Manfredi M, Marsden CD. The pathophysiology of primary dystonia. Brain 1998; 121: 1195 – 1212.
2. Haggstrom L, Darveniza P, Tisch S. Mild parkinsonian features in dystonia: literature review, mechanisms and clinical perspectives. Parkinsonism Relat Disord 2016 [Epub ahead of print].

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-kinematic-analysis-of-finger-tapping-in-dystonia/