Studies continued on long latency thyroarytenoid responses to superior laryngeal nerve stimulation resulting in vocal fold adduction in the awake human. The long latency response between 55 and 70 ms is thought to have the same neurophysiological basis as the cough reflex. This late response was decreased during phonation while an earlier ipsilateral response was enhanced, suggesting that the various laryngeal reflex responses may be modified differently by voluntary activity. Treatment with botulinum toxin in spasmodic dysphonic patients who had a return of symptoms following Type III Thyroplasty was evaluated and compared with previously untreated spasmodic dysphonic patients' responses to injection. Symptom improvements occurred following both unilateral and bilateral injections in the previously untreated patients, while the post thyroplasty group had few benefits following either type of injection. Thyroplasty may render spasmodic dysphonic patients unable to respond to other treatment approaches when symptoms return. The long-term effects of botulinum toxin injections were evaluated in patients who had received multiple treatments for their spasmodic dysphonia on one side. Units had longer durations on the injected side, although the number of turns, a measure of the number of unit firings, was not altered on the injected side. As the time following the last injection increased, fewer differences were found suggesting that physiological changes following an injection continue past one year.
