Brain-stem auditory-evoked potentials in spasmodic torticollis

M. E. Drake Jr
Department of Neurology, Ohio State University College of Medicine, Columbus 43210.

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.