To examine visual and vestibular spatial perception skills in patients with cervical dystonia.

Cervical dystonia (CD) is characterized by involuntary muscle spasm leading to abnormal postures or tremor of the head. Non-motor deficits in CD are increasingly recognized as determinants of quality of life and disability. CD patients are known to have impairment in tasks requiring the mental manipulation of surrounding space. We hypothesized that CD patients have abnormal heading perception in visual and vestibular domains, and that this correlates with severity of dystonia.

We recruited 12 CD patients and 4 healthy controls (HC). We examined vestibular motion perception with en bloc movement of a head-fixed platform (Hexapod, Moog) in which subjects experienced a step forward movement with randomized, variable degrees of directionality. We examined visual motion perception using immersive virtual reality goggles in which subjects viewed a star-cloud radiating from different locations on the horizon with randomized variable degrees of directionality. During both tasks, subjects selected leftward or rightward relative to perceived straight ahead motion. Statistical significance was investigated using the Student’s T-test.

CD group had significantly higher visual discrimination thresholds (6.91±3.16° vs 4.35±1.47°) [p=0.03] as well as vestibular discrimination thresholds (24.74±17.7° vs 12.14±5.6°) [p=0.02] than HC group. There was no significant difference in visual directional bias between CD and HC groups. CD group (-6.8±3.11°) had a significantly higher vestibular bias than HC group (0.1±3.37°) [p=0.001]. There was no significant difference between visual and vestibular thresholds and biases between CD patients with (n=6) and without (n=2) tremor. Higher TWSTRS score correlated with higher vestibular threshold (R² = 0.4263).

Vestibular and visual heading perception are impaired in CD. The impairment could be due to abnormal head-on-trunk orientation signal leading to inaccurate coordinate transformation necessary for perceiving direction of one’s own motion.