Utility of Underwater Peroral Endoscopic Myotomy with Near-Focus Magnification for Severe Submucosal Fibrosis.

Background Severe submucosal fibrosis (SMF) is the strongest predictor of technical failure and prolonged procedure time in conventional per-oral endoscopic myotomy (POEM). Underwater POEM (uPOEM) may offer advantages in fibrotic cases, but its effectiveness remains unexplored. Methods This is a single-center, retrospective case series of consecutive patients who underwent uPOEM using near-focus magnification for achalasia with SMF between July 2024 and December 2025. Results Of 153 POEM procedures, 12 patients had SMF (median age 56 [IQR 52-63] years, symptom duration 9 [IQR 7.2-10] years). Four were treatment-naive. Eight had type I (66.7%) and four (33.3%) type II achalasia. Sigmoid esophagus (S1) was present in 3 (25%), S2 in 2 (16.7%), and straight type in 7 (58.3%). The median integrated relaxation pressure (IRP) was 30 (IQR 27-33) mmHg. uPOEM was successfully completed in all 12 patients (100%) with near-focus magnification in whom uPOEM-assisted tunneling was initiated, after exclusion of one aborted pre-tunneling case. The median procedure time was 54 (IQR 52-58) min. One patient had a mucosal breach (Type I), managed with hemoclips. The median Eckardt score decreased significantly from 7 to 0 at 3 months ( p < 0.001). Conclusions uPOEM is safe and appeared feasible in severe SMF, yielding favorable short-term outcomes. Near-focus magnification allows better identification of the submucosal layer allowing for more precise dissection.