A 22-year-old woman has had multiple episodes of aspiration of food associated with difficulty swallowing during the past year. On auscultation of her chest, crackles are heard at the base of the right lung. A barium swallow shows marked esophageal dilation above the level of the lower esophageal sphincter. A biopsy specimen from the lower esophagus shows an absence of the myenteric ganglia. What is the most likely diagnosis?

In achalasia, there is incomplete relaxation of the lower esophageal sphincter with a lack of peristalsis. Most cases are "primary" or of unknown origin. They may be caused by degenerative changes in neural innervation; the myenteric ganglia are usually absent from the body of the esophagus. There is a long-term risk of development of squamous cell carcinoma. In Barrett esophagus, there is columnar epithelial metaplasia, but the myenteric plexuses remain intact. Reflux esophagitis may be associated with hiatal hernia, but myenteric ganglia remain intact. Plummer-Vinson syndrome is a rare condition caused by iron deficiency anemia; it is accompanied by an upper esophageal web. Systemic sclerosis (scleroderma) is marked by fibrosis with a stricture.