To compare technical, clinical success, adverse events rate and incidence of post-procedural pain of conventional PerOral Endoscopic Myotomy (POEM) versus underwater POEM (u-POEM) in consecutive patients treated for achalasia at a tertiary referral centre.

We retrospectively analysed POEM and u-POEM performed in our centre between February 2024 and July 2025 with at least 3 months of follow-up.  In u-POEM, CO₂ insufflation was suspended during tunnelling and myotomy and the submucosal space was filled with room-temperature saline. Pre-procedural (demographics, achalasia subtype, previous treatments, Eckardt score, laboratory exams), procedural (tunnel and myotomy length, tunnelling and myotomy speed, procedure time, anterior or posterior approach) and post-procedural (pain, laboratory exams, analgesics administration, adverse events evaluation) data were recorded. Statistical analysis was made using Student’s t-test or Wilcoxon rank-sum for continuous variables and Fisher’s exact test for categorical variables; two-sided p<0.05 was considered significant.

Twenty-five consecutive patients were included (POEM n=13; u-POEM n=12). Baseline demographics, BMI, ASA and Eckardt score were comparable. Technical success was reached in all patients. Clinical success (Eckardt score ≤3 at 3 months) was 100% in both groups. Mean total procedure time was significantly longer for u-POEM (68.8 ± 16.0 vs 56.2 ± 12.5 min; p=0.038), driven by a slower myotomy speed (0.85 ± 0.28 vs 1.44 ± 0.54 cm/min; p=0.003), while tunnelling speed and tunnel/myotomy lengths were similar between the two groups. Postoperative pain, measured 24 hours after the procedure using an NRS scale, was less intense in the group of patients who underwent u-POEM (median NRS 1.0 [IQR 0.0–2.25] vs 3.0 [IQR 3.0–4.0]; p=0.004) and 4/12 patients in u-POEM group reported no pain versus 0/13 in POEM (p=0.039). No major adverse events occurred; minor adverse events rate was lower with u-POEM (1/12, 8.3% vs 4/13, 30.8%; p=0.322) but without statistical significance.

u-POEM is feasible and achieved the same outcomes of POEM. This new technique is associated to a reduction of postoperative pain. This result is probably due to the less intense thermal effect on tissues.  On the other hand, u-POEM is associated with reduced myotomy speed. These findings support u-POEM as a safe, effective and less painful alternative to conventional POEM.