Clinical and electrophysiological evaluation of dysphagia in myasthenia gravis

Objective-To evaluate dysphagia at the oropharyngeal stage of swallowing an d to determine the pathophysiological mechanisms of dysphagia in patients w ith myasthenia gravis. Methods-Fifteen patients with myasthenia gravis with dysphagia and 10 patie nts without dysphagia were investigated by a combined electrophysiological and mechanical method described previously. Laryngeal movements were detect ed by a piezoelectric transducer and the related submental EMG (SM-EMG) and sometimes the EMG of cricopharyngeal muscle of the upper esophageal sphinc ter (CP-EMG) were recorded during dry or wet swallowing. The results of the se electrophysiological variables were compared with those of normal age ma tched control subjects. Results-In patients with myasthenia gravis with dysphagia, it was found tha t the time necessary for the larynx to remain in its superior position duri ng swallowing and swallowing variability in successive swallows increased s ignificantly compared with normal subjects and with patients with myastheni a gravis without dysphagia. The total duration of SM-EMG activity was also prolonged in both groups but more severely in the dysphagic patients. Elect romyographic activity of the CP sphincter was found to be normal in the dys phagic patients investigated. All the patients with myasthenia gravis with dysphagia had pathological dysphagia limits (<20 mi water) whereas other pa tients except two, were within normal limits. Conclusions-Because the electrophysiological variables related to oropharyn geal swallowing were prolonged even in patients with myasthenia gravis with out dysphagia, it is concluded that the submental and laryngeal elevators a re involved subclinically in myasthenia gravis and, because of compensating mechanisms, the patient may not be dysphagic. As the CP-EMG behaviour was found to be normal, a coordination disorder between normal CP sphincter mus cle and the affected striated muscles of the laryngeal elevators may be one of the reasons for dysphagia in myasthenia gravis. This method also made i t possible to investigate the myasthenic involvement in the laryngeal eleva tors that cannot be evaluated by other electrophysiological methods in myas thenia gravis.