Focal Hand Dystonia: A Functional Imaging Study

Writer's cramp is a focal task-specific dystonia that specifically affects the act of handwriting. Although it has been generally thought that sensation is normal, there is consistent evidence for defective perception (i.e., kinaesthesia, temporal and spatial discrimination) and abnormal sensory processing in focal hand dystonia. For instance, Tempel and Perlmutter demonstrated bilateral diminished regional blood flow response in the sensorimotor cortex in patients with unilateral dystonia after vibrotactile stimulation (Tempel and Perlmutter, Brain 1990; 113: 691–707). Here we used functional magnetic resonance imaging (fMRI) at 3 tesla to map functional brain activation associated with central processing of complex cutaneous stimuli during a “Grating Orientation Task“. The study included 12 patients with writer's cramp and 12 healthy age-matched controls. During fMRI, a hemispheric plastic dome (JVP-Domes; Stoelting, Wood Dale, IL; gap values: 0.35mm or 3.0mm) was positioned either vertically or horizontally on the tip of the right index finger. Participants were required to judge the orientation of the domes. Statistical analyses were performed using SPM2 software (Wellcome Department of Imaging Neuroscience, ION, London, UK). Significance threshold was set at P<0.05 (corrected). In patients with writer's cramp, the “Grating Orientation Task“ produced a stronger activation in the rostral dorsal premotor cortex, rostral supplementary motor area, precuneus, and occipital visual areas. Subcortically, the putamen, caudate nucleus, thalamus and cerebellum showed a relative increase in task related activity. Our results indicate that in patients with writer's cramp, complex tactile stimuli produce an abnormal increase in neuronal activity within the sensorimotor network. This may be a functional correlate of compensatory mechanisms or impaired centre-sorround inhibition during sensory processing.