Pathophysiological mechanisms of oropharyngeal dysphagia in amyotrophic lateral sclerosis

We investigated the pathophysiological mechanisms of dysphagia in amyotroph ic lateral sclerosis, Forty-three patients with sporadic amyotrophic latera l sclerosis were examined by clinical and electrophysiological methods that objectively measured the oropharyngeal phase of voluntarily initiated swal lowing, and these results were compared with those obtained from 50 age-mat ched control subjects. Laryngeal movements were detected by a piezoelectric sensor and EMG of submental muscles, and needle EMG of the cricopharyngeal muscle of the upper oesophageal sphincter of both the amyotrophic lateral sclerosis and control groups was recorded during swallowing. Amyotrophic la teral sclerosis patients with dysphagia displayed the following abnormal fi ndings. (i) Submental muscle activity of the laryngeal elevators, which pro duce reflex upward deflection of the larynx during wet swallowing, was sign ificantly prolonged whereas the laryngeal relocation time of the swallowing reflex remained within normal limits. (ii) The cricopharyngeal sphincter m uscle EMG demonstrated severe abnormalities during voluntarily initiated sw allows. The opening of the sphincter was delayed and/ or the closure occurr ed prematurely, the total duration of opening was shortened and, at times, unexpected motor unit bursts appeared during this period. (iii) During volu ntarily initiated swallows there was significant lack of co-ordination betw een the laryngeal elevator muscles and the cricopharyngeal sphincter muscle . These results point to two pathophysiological mechanisms that operate to cause dysphagia in amyotrophic lateral sclerosis patients. (i) The triggeri ng of the swallowing reflex for the voluntarily initiated swallow is delaye d and eventually abolished, whereas the spontaneous reflexive swallows are preserved until the preterminal stage of amyotrophic lateral sclerosis, (ii ) The cricopharyngeal sphincter muscle of the upper oesophageal sphincter b ecomes hyper-reflexic and hypertonic. As a result, the laryngeal protective system and the bolus transport system of deglutition lose their co-ordinat ion during voluntarily initiated swallowing, We conclude that these pathoph ysiological changes are related mainly to the progressive degeneration of t he excitatory and inhibitory corticobulbar pyramidal fibres.