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

ABSTRACT 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.