Achalasia and lower esophageal sphincter anatomy and physiology: Implications for peroral esophageal myotomy technique

The anatomical lower esophageal sphincter (LES) consists of 2 sphincters—the intrinsic sphincter involving the semicircular clasp muscles and the oblique sling muscle and the external sphincter, the crural diaphragm. Innervation is through the preganglionic vagus nerve fibers that release acetylcholine as the neurotransmitter affecting 2 types of postganglionic neurons in the myenteric plexus. The postganglionic excitatory neurons release acetylcholine and substance P. The major inhibitory neurotransmitter is nitric oxide, which promotes LES relaxation. Achalasia results from a loss of postganglionic inhibitory innervation resulting in aperistalsis and poor LES relaxation. The key to the surgical treatment of achalasia is adequate disruption of both the semicircular clasp muscles and oblique sling muscle with a myotomy extending at least 2 cm-3 cm onto the stomach. This nearly eliminates basal LES tone; therefore, a fundoplication is added to prevent reflux disease. The new POEM operation needs to include an adequate myotomy on the gastric side, but would the cost be severe acid reflux as no fundoplication is currently performed? Time will tell.