Dysphagia in lateral medullary infarction (Wallenberg's syndrome) - An acute disconnection syndrome in premotor neurons related to swallowing activity?

Background and Purpose-We have investigated the pathophysiological mechanis ms of dysphagia in Wallenberg's syndrome (WS) that are due to lateral medul lary infarction (LMI). Methods-Twenty patients with WS were evaluated by means of clinical and ele ctrophysiological methods that measured the oropharyngeal phase of voluntar ily initiated swallowing. For comparison, 22 patients with unilateral hemis pheric infarction were investigated during the acute stage of stroke, and 4 patients with unilateral peripheral 9th and 10th cranial nerve palsies wer e studied. Age-matched 30 healthy control subjects were also included in th e study. Results-It was found that dysphagia was clinically more severe in WS patien ts than in the patients in the other groups. The pharyngeal phase of swallo wing was predominantly impaired, whereas in patients with hemispheric strok e, dysphagia was related only to the delay of triggering of the voluntarily induced swallowing. In WS patients, the swallowing reflex was extremely sl ow in spite of the unilateral involvement due to LMI, whereas the pharyngea l phase of reflex swallowing remained within normal limits in patients with unilateral hemispheric stroke and patients with unilateral peripheral 9th and 10th cranial nerve palsies. Conclusions-Although in WS the lesion due to LMI is unilateral, its effect on oropharyngeal swallowing is bilateral. In LMI, primarily the premotor ne urons in the nucleus ambiguus and their connections seem to be affected. Co nsequently, a disruption and/or disconnection of their linkage to swallowin g-related cranial motor neuron pools bilaterally and to the contralateral n ucleus ambiguus could produce the swallowing disorders in WS. However, the remaining intact ipsilateral premotor neurons and the contralateral center in the medulla oblongata may eventually begin to operate and overcome the s everity and long-term persistence of dysphagia.