Achalasia subtypes are front and center of the Chicago classification-strategies to overcome limitations in clinical application

High-resolution manometry (HRM) with closely spaced pressure sensors, enhances visualization and interpretation of esophageal pressures. HRM software displays two key physiological features of achalasia: Inadequate swallow-induced lower esophageal sphincter (LES) relaxation, and the absence of normal esophageal primary peristalsis. HRM metrics quantify these features, by determining: (I) integrated relaxation pressure (IRP) of the esophagogastric junction (EGJ) during swallowing; and (II) esophageal body pressure patterns of absent or abnormal peristalsis, with high sensitivity for diagnosis of achalasia. These measures guide identification of three achalasia subtypes, through the Chicago classification of motility disorders. Achalasia subtypes stratify prevalent esophageal body pressure patterns with: Subtype I, absent pressures (aperistalsis); subtype II, uniform pressures (esophageal pan pressurization); and subtype III, spasm pressures (spastic, premature or abnormal contractions). Whenever HRM reveals a non-relaxing EGJ, achalasia subtypes are front and center of the hierarchical classification process, with relevance to treatment outcomes. Exploration of pathophysiology suggests esophageal circular and longitudinal muscle function varies with achalasia subtype. Beyond the classification, an achalasia-like syndrome refers to a minority of patients where pressures do not meet criteria for achalasia subtypes, necessitating adjunct tests. Application of HRM in patients with achalasia can be challenging. Limitations during acquisition may occur with resistance at the EGJ or catheter curling, and esophageal pooling with successive water swallows. Interpretation requires care when EGJ relaxation pressure is within the normal range or affected by longitudinal muscle contraction. To overcome inconclusive HRM findings, strategies to clarify dysmotility include adjunct swallow challenge tests or additional investigations. Evolving manometric protocols, additional HRM metrics, and incorporation of intraluminal impedance will maximize HRM utility for achalasia.