Clinical Application of the London Classification in 3D High‐Definition Anorectal Manometry: Prevalence, Limitations, and Complementary Metrics

BACKGROUND: The London classification (LC) standardizes the interpretation of anorectal manometry, but real-world data using high-definition three-dimensional anorectal manometry (3D HD-ARM) remain limited. OBJECTIVE: To characterize anorectal manometric patterns in a large 3D HD-ARM cohort applying the LC and to assess additional functional parameters not included in the classification. METHODS: We retrospectively analyzed 300 consecutive 3D HD-ARM studies with balloon expulsion testing (BET). Clinical subgroups were defined using validated questionnaires: St. Mark's score for anal incontinence (AI) and Knowles-Eccersley-Scott Symptom score for chronic constipation (CC). RESULTS: Anal incontinence (AI) was highly prevalent (81.7%), with 75.7% reporting moderate-to-severe fecal incontinence. CC was present in 56.7%, and 49.1% showed overlapping symptoms. The most frequent major finding was rectal hyposensitivity (43.3%) and anal normotension with hypocontractility (16.3%). Anal normotension with hypocontractility best correlated with AI [OR 14.5 (95% CI 1.9-110.2; p = 0.010)], while anal hypertension was more frequent in CC [OR 2.2 (95% CI 1.3-3.9; p = 0.005)]. Rectoanal coordination disorders were common, with inconclusive patterns in 54.4%, limiting diagnostic precision. Among constipated patients with obstructive defecation syndrome (ODS), pathological coordination was more frequent [OR 3.5 (95% CI 1.1-12.1; p = 0.040)]. Additional parameters not included in the LC-reduced functional anal canal length and shorter sustained squeeze duration-were more evident in women with AI, whereas ultraslow waves were associated with CC. Sphincter defects were detected in 13%, mainly in women and AI patients. CONCLUSION: The LC enables consistent phenotyping of anorectal dysfunction, highlighting major abnormalities as highly prevalent. However, frequent minor and inconclusive findings-particularly in defecatory coordination-underscore limitations of the current classification and the need for refinement.