Spasmodic torticollis following unilateral VIII nerve lesions: neck EMG modulation in response to vestibular stimuli.

Three patients with spasmodic torticollis following VIII nerve lesions (VIII-ST) underwent quantitative assessment of their sternomastoid EMG during vestibular (otolith and semicircular canal) stimulation. The results were compared with a normal control group and with six patients with idiopathic spasmodic torticollis (ST). Backwards tilt of the VIII-ST patients resulted in a marked increase in the EMG, especially in the more affected sternomastoid, whereas this manoeuvre did not have a significant effect in normal subjects, or had a variable effect in the ST group. These results suggest that those with torticollis following VIII nerve lesions are a distinct group. Since there was no relationship between the side of the VIII nerve lesion and the direction of the torticollis a direct aetiological link between the two is, however, unlikely. The unusual EMG/tilt responses are explained on the basis of peripheral imbalance of utricular signals (maximal in the supine position) in the presence of central deranged processing of information concerning head posture.