While the etiology of achalasia remains unclear, the histopathological changes associated with it have been well described. Surgical specimens involving strips of esophageal muscle from esophagomyotomy or entire resected esophagi have formed the basis of study.32-35 Gross examination of esophagectomy specimens from patients with severe/recurrent achalasia reveals the classic morphology of a dilated proximal esophagus, with distal tapering. The muscularis propria is frequently hypertrophied, and the mucosa exhibits exaggerated longitudinal folds.32
Upon microscopic examination, there is a range of associated changes in the esophagus. The most classic feature is an absence of myenteric ganglion cells, which is seen in specimens from patients with both early and late achalasia.32,34-38 While there is no apparent association between the number of remaining ganglion cells and the degree of symptoms, there does seem to be a temporal relationship, i.e. patients with longstanding disease tend to exhibit fewer ganglion cells.34,38 The most consistent histological feature, seen in all esophageal specimens, is inflammation.32,35 The inflammation occurs in and around the myen-teric nerves, predominantly involves lymphocytes and results in neural fibrosis. Goldblum et al made an interesting observation in their study of patients with early achalasia.35 A woman with rapid onset of dysphagia and weight loss underwent esophagomyotomy only 2.5 months after the onset of symptoms. Histological examination was significant for mild myenteric inflammation, normal numbers of ganglion cells and an absence of fibrosis. These findings suggest that the earliest pathological feature of achalasia is myenteric inflammation.
Additional histological changes result from esophageal obstruction and the associated stasis. Esophageal obstruction leads to varying degrees of muscular hypertrophy of the muscularis propria, most notably in the inner circular layer.32,36,39 Further findings include small leiomyomas of the inner circular layer, degenerative changes of the muscularis propria as well as focal fibrosis of the muscularis propria (again, predominantly in the inner circular layer).32 Stasis of luminal contents results in both proximal and distal squamous hyperplasia, as well as changes similar to those seen in reflux esophagitis, namely papillomatosis and basal cell hyperplasia.32 However, owing to the increased LES pressure limiting passage of gastric contents, these findings are unlikely to be due to true gastroesophageal reflux.
Extra-esophageal pathology accompanies achala-sia, predominantly related to esophageal innervation. Both the vagus nerve and the vagal dorsal motor nucleus are affected. Electron microscopy of periesophageal vagal nerve biopsies reveals changes resembling Wallerian degeneration (i.e. secondary to nerve transaction), changes that are not seen on light microscopy.33,38 Whether the affected nerves are motor, sensory or vagal-associated sympathetic nerves is unclear. Evaluation of the dorsal motor nucleus of the vagus, performed upon autopsy, also reveals degenerative changes, neuron loss and Lewy bodies.40
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