Since its introduction into clinical practice nearly a decade ago, per-oral endoscopic myotomy (POEM) has now become an accepted minimally invasive approach for the treatment of achalasia with excellent short- and mid-term clinical outcomes in both treatment naïve and those who have failed prior therapy. POEM is comparable to laparoscopic Heller myotomy (LHM) in terms of efficacy and safety, with less procedural pain and faster recovery time. Recent data also reveals that POEM may be more effective and durable than pneumatic dilation (PD) for the treatment of achalasia, with similar safety profile. Preliminary data on POEM for spastic esophageal disorders (SED) is promising yet scarce. Post-POEM gastroesophageal reflux disease (GERD) is common but asymptomatic in most patients, further highlighting the need for ongoing research in this field and the importance of long-term surveillance of these patients.

OPINION STATEMENT: "Third space" endoscopy, also commonly referred as submucosal endoscopy, is founded on the principle that the deeper layers of the gastrointestinal (GI) tract can be accessed by tunneling in the submucosal space without compromising the integrity of the overlying mucosa. Peroral endoscopic myotomy (POEM), endoscopic submucosal dissection (ESD), and submucosal tunneling endoscopic resection (STER) are innovative techniques within the field of third space endoscopy in the management of esophageal disorders. POEM has become an accepted minimally invasive therapy for achalasia and related motility disorders with excellent short-term results, with early studies yielding similar efficacy to surgical myotomy and increased durability when compared to pneumatic balloon dilation (PBD). Data are needed to establish long-term outcomes with POEM, with particular interest on the incidence of gastroesophageal reflux, which appears to be higher than initially anticipated. ESD, a mature endoscopic resection technique in Asia, has recently gained traction in the West as a viable option for the management of early Barrett's esophagus (BE) neoplasia. Compared to standard endoscopic mucosal resection (EMR), ESD allows the en bloc resection of lesions irrespective of size, which may facilitate histological interpretation and reduce recurrence rates. Large prospective randomized controlled trials are needed to validate the efficacy and safety of this technique and to further define its role in the endoscopic armamentarium in early BE neoplasia. STER is an attractive technique that theoretically permits the resection of subepithelial esophageal tumors (SETs) arising from the deeper GI layers. Initial studies from highly experienced endoscopic centers support its technical feasibility and safety, although these results should be interpreted with caution due to variability arising from small numbers and heterogeneity among studies. Overall, third space endoscopy is an expanding field within endoscopic therapeutics for the treatment of esophageal diseases. While initial results have been very promising, large prospective studies, long-term data, and structured training programs with the establishment of competency parameters are needed before third space endoscopy can be advocated outside of highly specialized centers.

Peroral endoscopic myotomy (POEM) was first performed in 2008 as a novel treatment of achalasia. It is now performed globally, demonstrating the evolution of the first successful natural orifice transluminal endoscopic surgery (NOTES) procedure. There is extensive data demonstrating the safety and efficacy of POEM, and now long-term data has emerged demonstrating that the efficacy is durable. POEM is also being used to successfully treat diffuse esophageal spasm (DES) and jackhammer esophagus. With jackhammer esophagus and DES, inclusion of the lower esophageal sphincter in the myotomy minimizes the risk of symptom development from iatrogenic ineffective esophageal motility.

Historically, the most robust outcomes in treatment of achalasia were seen with surgical myotomy. Per oral endoscopic myotomy (POEM) introduced an endoscopic method for creating a surgical myotomy. Thousands of cases of POEM have been performed; however, there is no standard technique, and the rates of clinical success and adverse events vary widely among centers. This article presents a detailed description of the POEM technique, including the rationale and potential pitfalls of the main variations, in the context of the international literature.

Peroral endoscopic myotomy (POEM) was first performed in Japan in 2008 for uncomplicated achalasia. With excellent results, it was adopted by highly skilled endoscopists around the world and the indications for POEM were expanded to include advanced sigmoid achalasia, failed surgical myotomy, patients with previous endoscopic treatments and even other spastic oesophageal motility disorders. With increased uptake and performance of POEM, variations in technique and improved management of adverse events have been developed. Now, 6 years since the first case and with >3,000 procedures performed worldwide, long-term data has shown the efficacy of POEM to be long-lasting. A growing body of literature also exists pertaining to the learning curve, application of novel technologies, extended indications and physiologic changes with POEM. Ultimately, this once experimental procedure is evolving towards becoming the preferred treatment for achalasia and other spastic oesophageal motility disorders.