A 32-year-old man presents with dysphagia to both liquids and solids, occasional regurgitation of undigested food, and weight loss. Barium swallow shows a dilated oesophagus with a smooth tapering ('bird beak') distal segment. Manometry shows failure of the lower oesophageal sphincter to relax on swallowing. The pathophysiologic defect is:

• A Degeneration of inhibitory (nitrergic and VIPergic) myenteric neurons, leaving the sphincter tonically contracted ✓
• B Loss of excitatory cholinergic neurons supplying the lower oesophageal sphincter
• C Excess circulating cholecystokinin causing sustained sphincter contraction
• D Damage to the nucleus ambiguus abolishing the swallowing reflex

Explanation

Lower oesophageal sphincter relaxation during swallowing depends on inhibitory postganglionic neurons releasing nitric oxide and VIP from the myenteric plexus. In idiopathic achalasia these inhibitory neurons degenerate, so the sphincter cannot relax and aperistalsis develops, producing the bird beak appearance. Excitatory cholinergic function is relatively preserved, which is why the sphincter tone is actually increased, not lost. The swallowing reflex itself remains intact.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.