Histopathologic Characteristics in Per-oral Endoscopic Myotomy Biopsy Among Achalasia Subtypes

Achalasia is an esophageal motility disorder categorized into three subtypes based on esophageal motility patterns assessed by high-resolution manometry (HRM). This study aimed to evaluate and compare the histopathological characteristics of the muscularis propria at the lower esophageal sphincter (LES) and the esophageal body among different achalasia subtypes.

A total of 26 patients initially diagnosed with achalasia and undergoing peroral endoscopic myotomy (POEM) between May 2021 and November 2022 were prospectively enrolled. During POEM, biopsy specimens of the muscularis propria were obtained from the LES and the distal esophagus (approximately 5 cm above the LES). Tissue sections were stained with hematoxylin and eosin (H&E) and Masson's trichrome, and immunohistochemical staining was performed for CD117, S100, CD3, CD20, CD4, and CD8. Control samples of histologically normal LES tissue were obtained from five patients undergoing surgery for gastric malignancy.

Of the 26 patients, 14 (53.8%) were classified as type I and 12 (46.2%) as type II achalasia. The esophageal diameter was significantly larger in type I than in type II achalasia (4.57 ± 1.09 cm vs. 3.25 ± 0.88 cm, p = 0.005). At the LES, the degree of fibrosis and the proportion of severe ganglion loss in the muscularis propria were significantly higher in type I achalasia than in controls (p < 0.05). The number of interstitial cells of Cajal (ICCs) was significantly lower in type I achalasia compared to controls (p = 0.031). Although a difference was observed in CD4 + T cell counts among type I, type II, and control groups (p = 0.045), post-hoc pairwise comparisons did not reveal significant differences. No significant differences were observed in the distal esophagus and the LES regarding inflammation, fibrosis, ganglion loss, ICC density, or counts of CD3 + , CD4 + , CD8 + , or CD20 + cells (p > 0.05). Mild fibrosis was more frequently observed in the distal esophagus than in the LES, but this difference was not statistically significant (p > 0.05).

Compared to controls, type I achalasia is associated with significantly greater fibrosis, more severe ganglion loss, and a reduced number of ICCs in the muscularis propria at the LES. These findings suggest that type I achalasia may represent an advanced stage of the disease, characterized by inflammation-driven ganglion degeneration, loss of ICCs, and progressive fibrosis.