Abnormal response from the sternocleidomastoid muscle in patients with spasmodic torticollis: observations during microvascular decompression operations.

Electromyographic (EMG) recordings from patients undergoing microvascular decompression (MVD) operations to relieve spasmodic torticollis were studied. When EMG potentials were recorded from the sternocleidomastoid muscle in response to electrical stimulation of the spinal accessory nerve (SAN) at the neck, an abnormal (delayed) response was seen in 9 of 12 patients who had unilateral symptoms. In 5 patients with bilateral symptoms, no such delayed response was seen. We assume that this abnormal muscle response depends on an abnormal cross-transmission. Neural conduction time measurements, using electrical stimulation of the intracranial portion of the SAN, indicated that the location of this cross-transmission was more central than the vascular compression of the SAN. We hypothesize that this location might be in the motonucleus of the SAN. Similarities between these abnormal EMG findings in patients with spasmodic torticollis and those reported earlier in patients with hemifacial spasm (HFS) are presented.