Definition, incidence and etiology: what's new in the 21st century?

Actually, achalasia can be defined as a primary esophageal motor disorder characterized by esophageal aperistalsis and abnormal post-deglutitive lower esophageal sphincter (LES) relaxation. Its incidence varies from 0.03 to 1.63 cases per 100,000 people per year and increases with age, while the prevalence is almost 10/100,000 with no difference between the sexes. Regarding etiology, the most frequent histologic alteration is represented by the loss of the myenteric nerve fibers regulating inhibitory nitrergic neurotransmission in the LES, with the presence of a lymphocytic infiltrate and collagen deposition. The cause of this loss remains unclear. Among the theories proposed, the infectious, hereditary and autoimmune etiologies have been widely investigated. The only infectious agent identified as a cause of achalasia is Trypanosoma Cruzi, responsible of Chagas' disease. Regarding hereditary component, in rare cases achalasia presents as part of a genetic syndrome such as Down syndrome, Allgrove syndrome and familial visceral neuropathy. Although, no disease-specific gene has been identified. The autoimmune hypothesis has focused on the association of specific HLA classes with achalasia. However, no consistent association has been observed across studies. Despite increasing understanding of the physiopathology of achalasia, its etiology remains largely unknown. The onset of the disease is characterized by chronic inflammation of the myenteric plexus of the esophagus secondary to an environmental insult. Probably, genetic factors are involved in the development of achalasia, although the precise molecular basis of the disease has not been identified.