Major Basic Protein Deposition Without Eosinophilic Infiltration in Hypercontractile Esophagus: A Case Report

Hypercontractile esophagus is a motility disorder characterized by excessive contractions in the esophageal body. Certain cases of hypercontractile esophagus exhibit eosinophilic infiltration in the muscle layer; however, its clinical significance is unclear. Here, we report a case of hypercontractile esophagus with possible eosinophilic inflammation despite the absence of eosinophilic infiltration on hematoxylin and eosin staining. A 75-year-old man presented with dysphagia, primarily triggered by the ingestion of meat. Esophagogastroduodenoscopy showed abnormal peristalsis of the esophageal body, while the lower esophageal sphincter function remained normal. High-resolution manometry confirmed hypercontractile esophagus, according to the Chicago Classification version 4.0. As symptoms persisted despite medical treatment, the patient underwent peroral endoscopic myotomy. Biopsies obtained from the inner circular muscle layer revealed no notable eosinophilic infiltration on hematoxylin and eosin staining. However, immunofluorescence staining for major basic protein (MBP), a cytotoxic eosinophil granule protein that persists in tissues, showed patchy depositions. Corresponding counterstaining revealed collapsed nuclei surrounded by eosinophilic material, suggesting MBP release via eosinophil cytolysis. This case demonstrated that immunostaining for eosinophil granule proteins may uncover eosinophilic activity in the esophageal muscle layer, even in the absence of eosinophils. While the precise pathogenic role of eosinophilic inflammation in hypercontractile esophagus remains unclear, MBP deposition could reflect a localized immune-mediated process contributing to motility disturbance. Further investigation is needed to determine the prevalence, mechanisms, and clinical implications of these findings in esophageal motor disorders.