Eosinophilic esophageal myositis diagnosed by endoscopic ultrasound-guided fine-needle aspiration biopsy: a case report.

Eosinophilic esophagitis (EoE) is diagnosed by microscopic findings of eosinophilic infiltration into the squamous epithelium. In contrast, another disease concept termed "eosinophilic esophageal myositis (EoEM)" has been proposed, whereby there is eosinophilic infiltration into the muscularis propria instead. A 60-year-old man was referred to our hospital for chest pain, dysphagia, and several episodes of esophageal food impaction. Although EoE was suspected based on clinical features, biopsy specimens showed no mucosal eosinophilic infiltration. Endoscopic ultrasound (EUS) showed thickening of the muscularis propria layer and subsequent EUS-guided fine-needle aspiration biopsy (EUS-FNA) revealed eosinophilic infiltration into the muscularis propria. Although the patient's symptoms gradually improved after steroid administration, complete remission was not achieved after 1 year of treatment. This case may reflect a disorder distinct from typical EoE based on eosinophilic infiltration of the muscularis propria but not the squamous epithelium, and we, therefore, diagnosed it as EoEM using the EUS-FNA findings as reference.