Introduction: We tested whether a change in head/neck position initiates head deviation in drug-naïve patients with cervical dystonia and to identify the electrophysiological and neuroanatomical correlates of dystonic head rotation.
Methods: Twenty-five consecutive drug-naïve patients with cervical dystonia and 25 healthy controls underwent the simultaneous surface electromyographic (EMG) recording of sternocleidomastoid (SCM) muscle contractions during head/neck position changes, blink reflex recovery cycle (BRrc), DAT-SPECT, and advanced structural neuroimaging analysis using voxel-based morphometry (VBM).
Results: Surface EMG recordings of SCM muscle activity during changes in head/neck position demonstrated an insignificant asymmetric low amplitude of the SCM muscle contractions in the horizontal position in both patients and controls, but an asymmetric high amplitude in SCM muscle contractions leading to abnormal head movements in vertical positions in patients with cervical dystonia. All controls had a symmetric low increase in amplitude of SCM muscle contractions in response to changes in head/neck position. VBM analysis in 19 patients showed abnormal decreases of gray matter (GM) volume in the bilateral motor (localized in the homunculus of the head) and premotor cortices when compared to controls. In addition, the side of these neuroanatomical changes was asymmetrically related to abnormal head deviations in these patients. All subjects had normal results during BRrc and DAT-SPECT.
Conclusions: The passage from inactive horizontal position to active vertical head/neck posture initiates head deviation in drug-naïve patients with cervical dystonia, and the anatomical correlates of this dystonic head rotation is a restricted abnormal pattern of GM changes in the motor cortices.
Keywords: Dynamic dystonic disorder; Isolated cervical dystonia; Torticollis.
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