PATHOPHYSIOLOGY OF ACHALASIA
Achalasia is a primary esophageal motility disorder characterized by abnormal relaxation of the lower esophageal sphincter (LES) and absent esophageal peristalsis. The incidence rate is approximately 1 in 100,000, and the prevalence is approximately 10 in 100,000.1 This uncommon disease stands out among the esophageal motility disorders as the most clearly defined and successfully treated. Although this disease has well-defined clinical, manometric, and radiographic signs, the etiology is still unknown. Proposed etiologies include autoimmune, neurodegenerative, viral, and hereditary processes that, whether alone or in combination, lead to an inflammatory response that results in loss of inhibitory myenteric neurons.2
Dysphagia is one of the most predominant symptoms (in >90%) of achalasia patients. It results from the dysfunction of the ganglionic myenteric neurons that regulate esophageal peristalsis and LES relaxation in response to a food bolus.3 Other symptoms include regurgitation of undigested food and saliva (in 75% of patients), weight loss (in 60% of patients), chest pain (in 40% to 50% of patients), and heartburn (in 40% of patients).4,5
The clinical presentation of achalasia typically begins with intermittent dysphagia, which patients typically describe as a slower movement of the food with rapid eating. During this phase, the main complaint is chest pain secondary to esophageal spasms, without regurgitation of food.
During the next stage, patients develop esophageal spasms with immediate regurgitation of food. A third stage consists of chest pain and evidence of esophageal dilation. In the majority of the cases, weight loss is present at this latter stage. Once the esophagus is dilated, bland undigested food or saliva regurgitates at irregular intervals, which increases the risk of bronchopulmonary aspiration.1,6 Few data describe the esophageal manometric changes between stages7 and the environmental versus genetic factors that accelerate or decelerate disease progression. Interestingly, some patients progress from early to end-stage disease in a short period, while others may linger at initial phases for years. Misdiagnosis as gastroesophageal reflux disease (GERD) can delay appropriate diagnosis and treatment.8 Achalasia patients frequently develop shoulder and neck postural mechanisms to move swallowed food across the tonic LES.9
The diagnosis of achalasia is based on the sum of the evidence collected during endoscopic, radiographic, and manometric assessment.10 High-resolution manometry (HRM) plays an essential role in the assessment of esophageal motor function. The manometric findings of absence of peristalsis, hypertensive LES, and a poorly relaxing LES confirm the diagnosis.11 The combination of an atonic esophageal body with a functional obstruction at the gastroesophageal junction (GEJ) leads to incomplete bolus transit. The Chicago Classification of esophageal motility disorders (version 3.0) using HRM describes three subtypes of achalasia that are characterized by the pattern of aperistaltic contractions in association with an elevated integrated relaxation pressure (IRP) >15 mm Hg. Type I ...