A 30-year-old man consults a physician because he has been having increasing difficulty in swallowing both solids and liquids. Physical examination of the patient is noncontributory. Barium swallow studies show a mostly dilated esophagus with slow passage of barium into the stomach. The very distal pa of the esophagus appears narrowed into a "bird's beak." Esophageal manometry shows incomplete relaxation of the lower esophageal sphincter in response to swallowing, high resting lower esophageal pressure, and absent esophageal peristalsis. This patient's condition is MOST likely due to which of the following?

Individuals who have achalasia have been found to have a deficiency of inhibitory ganglion cells within the esophageal wall. This lack causes an imbalance in excitatory and inhibitory neurotransmission, with the result that the lower esophageal sphincter tends to have a higher-than-normal muscle tone and relaxes only with difficulty.Acid reflux can cause esophageal irritation, ulceration, and also predisposes for Barrett's metaplasia with subsequent risk of adenocarcinoma of the esophagus.Cancerous destruction would produce a mass, or area of stricture or ulceration.Candida infection of the esophagus resembles thrush of the mouth, and causes a usually superficial infection. Also Know:Achalasia is associated with a slightly increased risk of squamous carcinoma.An impoant complication of achalasia is aspiration of the contents of the dilated esophagus into the trachea, leading to recurrent attacks of aspiration pneumonia Ref: Chandrasoma P., Taylor C.R. (1998). Chapter 37. The Esophagus. In P. Chandrasoma, C.R. Taylor (Eds), Concise Pathology, 3e.