To characterize human thyroarytenoid and cricothyroid muscle responses to stimulation of the internal (sensory) and external (motor) branches of the superior laryngeal nerve (SLN), three awake subjects were studied at rest and during muscle activation with stimulation at different current levels. When only the external branch was stimulated, direct cricothyroid muscle responses were obtained without responses in either thyroarytenoid muscle. When only the internal branch was stimulated, no cricothyroid responses were obtained, but two late thyroarytenoid responses occurred (R1 and R2). The R1 response was usually ipsilateral and had a mean onset latency of 18 milliseconds, while the R2 response was bilateral and occurred between 66 and 70 milliseconds. Both responses tended to decrease in latency and increase in amplitude with increased stimulation level. The similarity of R1 to the adductor response and R2 to other late responses is discussed.

Eight patients with voice tremor were studied to characterize laryngeal muscle involvement. Electromyographic (EMG) recordings were made from intrinsic laryngeal muscles, simultaneously with some extrinsic laryngeal muscles, respiratory movement, and voice recordings during respiration, whisper, and phonation. Spectral measures were used to determine the tremor frequency and the prominence of spectral peaks in the EMG, respiratory and acoustic signals, while correlation coefficients were computed between pairs of tremulous EMG signals to measure the synchrony of tremor between muscles. The intrinsic laryngeal muscles were tremulous during respiration and speech, with the thyroarytenoid most often involved. Tremor was also detected in some of the extrinsic muscle recordings and the percentage of muscles with tremor was higher during phonation than during whisper or respiration. Time delays were found between tremor oscillations in laryngeal muscles. Because the thyroarytenoid was affected in all the patients studied, botulinum toxin injections may be beneficial in treatment of this voice disorder.

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We report the case of a 37-year-old woman with a history of long-standing right-sided sensorineural hearing loss who presented with an acute onset of vertigo and ipsilateral facial palsy. A computed tomographic scan study showed a stenosis of the right internal auditory canal (IAC). Neither generalized skeletal disease nor bony tumors, which may cause the IAC stenosis, were evident. The IAC stenosis found in this patient may be due to congenital malformation. Inflammation, compression or ischemia in the stenosed IAC may have resulted in the vertigo and facial palsy. This is the only case that we are aware of in which IAC stenosis is accompanied by vertigo and facial palsy.

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