Pathogenesis of achalasia cardia

Abstract

Achalasia cardia is one of the common causes of motor dysphagia. Though the disease was first described more than 300 years ago, exact pathogenesis of this condition still remains enigmatic. Pathophysiologically, achalasia cardia is caused by loss of inhibitory ganglion in the myenteric plexus of the esophagus. In the initial stage, degeneration of inhibitory nerves in the esophagus results in unopposed action of excitatory neurotransmitters such as acetylcholine, resulting in high amplitude non-peristaltic contractions (vigorous achalasia); progressive loss of cholinergic neurons over time results in dilation and low amplitude simultaneous contractions in the esophageal body (classic achalasia). Since the initial description, several studies have attempted to explore initiating agents that may cause the disease, such as viral infection, other environmental factors, autoimmunity, and genetic factors. Though Chagas disease, which mimics achalasia, is caused by an infective agent, available evidence suggests that infection may not be an independent cause of primary achalasia. A genetic basis for achalasia is supported by reports showing occurrence of disease in monozygotic twins, siblings and other first-degree relatives and occurrence in association with other genetic diseases such as Down's syndrome and Parkinson's disease. Polymorphisms in genes encoding for nitric oxide synthase, receptors for vasoactive intestinal peptide, interleukin 23 and the ALADIN gene have been reported. However, studies on larger numbers of patients and controls from different ethnic groups are needed before definite conclusions can be obtained. Currently, the disease is believed to be multi-factorial, with autoimmune mechanisms triggered by infection in a genetically predisposed individual leading to degeneration of inhibitory ganglia in the wall of the esophagus.

Keywords: Esophageal sphincter; Esophagus; Motility disorder; Motor dysphagia; Peristalsis.

Figure 1

Schematic diagram outlining possible pathogenesis of achalasia cardia. A: Diagram showing distribution of nitric oxide (NO) and acetycholine (Ach) neurons in the esophagus with normal motility pattern and barium esophagogram; B: Loss of NO in esophagus in early stage of the disease resulting in high amplitude simultaneous contractions in body (called vigorous achalasia). In this stage esophagus is not dilated in barium esophagogram; C: Further degeneration of inhibitory and additional degeneration of excitatory neurons causes low amplitude simultaneous contractions in esophageal body (called classic achalasia). In this stage esophagus is dilated in barium esophagogram. NANC: Non-adrenergic, non-cholinergic.