**Core Concept**
Achalasia is a primary esophageal motility disorder characterized by the failure of the lower esophageal sphincter (LES) to relax, leading to impaired esophageal emptying and progressive dilatation of the esophagus. This condition results from degeneration of the myenteric plexus, a network of nerve fibers controlling esophageal peristalsis.

**Why the Correct Answer is Right**
The degeneration of the myenteric plexus disrupts the coordinated contraction and relaxation of the esophageal muscles, preventing normal peristalsis and causing food accumulation in the esophagus. The failure of the LES to relax prevents the passage of food into the stomach, exacerbating dysphagia. This pathophysiological mechanism is responsible for the clinical manifestations of achalasia.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as achalasia is not caused by a mechanical obstruction, such as a tumor or stricture, which would require a different treatment approach.

**Option B:** This option is incorrect as achalasia is not associated with an abnormality in the esophageal muscles themselves, but rather with a dysfunction of the myenteric plexus controlling the muscles.

**Option C:** This option is incorrect as the primary cause of achalasia is not inflammation, but rather degeneration of the myenteric plexus.

**Option D:** This option is incorrect as the primary symptom of achalasia is not regurgitation of food, but rather progressive dysphagia.

**Clinical Pearl / High-Yield Fact**
Achalasia is often associated with other conditions, such as gastroesophageal reflux disease (GERD) and esophageal cancer, due to prolonged exposure of the esophagus to gastric reflux.

**Correct Answer:** C.