When Manometry and Functional Lumen Imaging Probe Disagree: The Current Limitations of the Chicago Classification Version 4.0 and Probable Extended Indications of Functional Lumen Imaging Probe.

High-resolution manometry (HRM) has revolutionized evaluation of esophageal motility disorders, offering detailed pressure topography and refined diagnostic criteria codified through the Chicago classification (CC). However, patients with dysphagia may present with borderline or near-normal HRM findings, exhibiting clinically significant symptoms. CC version 4.0 (v4.0) addresses such scenarios by recommending provocative maneuvers and ancillary tests, notably functional lumen imaging probe (FLIP) and timed barium esophagography. However, growing evidence indicates that FLIP, which measures luminal distensibility under balloon distention, can detect structural or biomechanical abnormalities, such as hypertrophy or fibrosis, that remain inconspicuous on HRM. These discordant findings point to limitations in CC v4.0. FLIP complements HRM by assessing passive tissue properties and capturing balloon-induced contractility, thereby unmasking subtle esophageal wall stiffness not always reflected in integrated relaxation pressure or standard peristaltic metrics. Such discrepancies can arise in early or atypical achalasia, esophagogastric junction outflow obstruction, eosinophilic esophagitis, and even epiphrenic diverticula, where "normal" manometry may belie significant pathology. Present CC v4.0 guidelines do not specify how to incorporate FLIP-derived measures or reconcile disagreements with timed barium esophagography results, leaving certain phenotypes-including repetitive simultaneous contractions-under-recognized. These gaps underscore an overreliance on integrated relaxation pressure alone and insufficient integration of evolving FLIP technology. Thus, standardizing FLIP protocols, establishing normative distensibility data, and clarifying management pathways for manometry-FLIP discordance remain critical. Prospective, multicenter studies are needed to investigate long-term clinical outcomes and to refine how FLIP metrics can be formally integrated into future CC iterations. Ultimately, multimodal, symptom-driven approaches that leverage both HRM and FLIP are essential to fully characterize esophageal dysmotility and optimize therapy.