The primary pathophysiologic abnormality in achalasia is loss of intrinsic inhibitory innervation of the lower esophageal sphincter and smooth muscle segment of the esophageal body. Disease of the extrinsic (vagal) nervous system and esophageal musculature may also be present, but these are less consistent findings and could represent secondary phenomena. Inflammation within the esophageal myenteric plexus is pathognomonic of the disease, but the cause of this inflammation is uncertain. Autoimmunity and previous viral infection have been hypothesized, but remain unproven.