Objective: Aim of the current study is to describe how patients with idiopathic cervical dystonia (CD) perform reaching movements with their upper limb (i.e. a clinically unaffected segment).

Background: CD is a focal dystonia, characterized by involuntary, abnormal movements and postures of the head and neck. Current views on its pathophysiology are faulty sensori-motor integration and impaired motor planning due to circuitry abnormalities between sensorimotor cortexes, cerebellum and basal ganglia. Previous studies showed end-effector kinematic abnormalities when CD patients perform upper limb reaching movements. However, evidence on this topic is still sparse.

Methods: CD patients attending the outpatient Movement Disorders Clinic of IRCCS Fondazione Don Gnocchi in Milan were recruited; prompted by a visual go signal, were asked to move a conventional PC mouse on a digitizing tablet so that to perform reaching towards targets displayed on a computer screen. During the task, subjects sat facing a computer monitor at eye level. Different movement parameters were calculated from the end-effector trajectory, such as spatial error and movement time. Patients were also evaluated with different clinical tests (TWSTRS, Beck’s, Zung, EQ5D5L, Rey figure). Median and IQR (between squared brackets) are used for descriptive statistics and the Wilcoxon rank sum test was used for between groups (controls vs CD patients) comparison.

Results: 9 patients with idiopathic CD and 7 healthy control subjects were recruited. With respect to controls, CD patients’ reaching movements had significantly longer movement time (controls: 0.39 [0.06] s vs patients: 0.45 [0.14] s; p=0.04), lower peak velocity (25.7 [2.24] cm/s vs 18.0 [6.73] cm/s; p<0.01) and lower peak acceleration (239.2 [38.2] cm/s² vs 150.8 [68.4] cm/s²; p=0.01). Movement extent was slightly smaller in CD patients (4.0 [0.3] cm) than controls (4.21 [0.32] cm; p=0.07). No between groups difference was present for movement error, onset time, trajectory area and symmetry index.

Conclusions: idiopathic CD patients show impaired reaching movements, despite no clinical signs of disease in their upper limbs. Our results are in line with previous observations. The effectiveness of a multimodal treatment consisting in botulinum toxin injections in cervical muscles coupled to sensori-motor re-learning techniques affecting plasticity remains to be investigated.

References: 1.Albanese A, Bhatia K, Bressman SB et al. Mov Disord, 2013; 28(7): 863-73. 2.Pelosin E, Bove M, Marinelli L et al. Mov Disord, 2009; 24(13): 1955-1961.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/impaired-reaching-movements-in-idiopathic-cervical-dystonia-patients/