Brain-stem auditory-evoked potentials in spasmodic torticollis.

The pathophysiology of idiopathic spasmodic torticollis is uncertain. Cerebral, basal ganglia, brain-stem, and cervicomedullary lesions have been implicated. Some investigators have found evoked-potential abnormalities, while others have not. We recorded brain-stem auditory-evoked potentials in six patients with otherwise normal result of examinations and laboratory studies. Brain-stem auditory-evoked potentials were recorded from Cz-A1 and Cz-A2 with rarefaction clicks delivered at 11.1/s and 70 dB above sensory threshold with 40-dB contralateral masking. Analysis time was 10 ms, filter bandpass was 150 to 3000 Hz, and 4000 averages were replicated. Patients and age-matched controls were compared by Student's t test. One patient had I-III and I-V interpeak latencies (IPLs) beyond clinical norms (99% tolerance limit). Mean IPLs ipsilateral to torticollis were 2.32 +/- 0.2 (I-III), 1.96 +/- 0.4 (III-V), and 4.16 +/- 0.3 (I-V). Contralateral IPLs were 2.0 +/- 0.2 (I-III), 2.0 +/- 0.2 (III-V), and 3.9 +/- 0.5 (I-V). Control values were 2.04 +/- 0.2 (I-III), 1.86 +/- 0.2 (III-V), and 3.86 +/- 0.4 (I-V). Absolute latencies, V/I amplitude ratios, and III-V IPLs did not differ significantly between patients and controls, nor did IPLs contralateral to torticollis. Ipsilateral I-III and I-V IPLs were greater in patients than in controls. These findings are consistent with those of some clinical reports and with experimental evidence that brain-stem lesions produce torticollis. They imply brain-stem dysfunction ipsilateral to head deviation in at least some patients with torticollis.