Brainstem and vagal dysfunction in pharyngoesophageal and esophageal dysphagia

Dysphagia affects approximately 16% of the US population and is classified as pharyngoesophageal and esophageal, the former being more clinically urgent because loss of airway protection may cause pulmonary aspiration and death. Safe swallowing depends on a brainstem central pattern generator, modulated by cortical and subcortical input and executed through the cranial nerves, above all the vagus. The latter supplies the pharynx, larynx, upper esophageal sphincter, esophagus and lower esophageal sphincter. Because afferent and efferent pathways converge in the medulla, small lesions in medulla cause severe, persistent dysphagia, worse than that following cortical injury. Dysphagia occurs in 80-90% of acute medullary strokes. Injury to the nucleus tractus solitarius degrades the sensory feedback that triggers the swallow, while nucleus ambiguous involvement weakens motor drive, producing delayed reflex triggering, pharyngeal muscle weakness, impaired sphincter opening, and silent aspiration. Vagal injury causes dysphagia at multiple levels, from unilateral palatal, pharyngeal, and laryngeal paresis to life-threatening bilateral paralysis, and loss of normal esophageal peristalsis. Because conventional manometry detects only the contraction phase of peristalsis, distension-contraction plots are needed to uncover distension-phase abnormalities in patients when pressure recordings appear normal, both in the pharynx and esophagus.