London ClassificationHRM-ARM Pathophysiology Interpreter
mmHg
mmHg
Functional Analysis
Input anal sphincter pressures and push maneuver profiles to generate a standardized London Classification report.
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
Evaluation of chronic constipation refractory to standard medical therapy
Workup for fecal incontinence (assessment of sphincter integrity and sensation)
Suspected Hirschsprung disease (specifically searching for the absence of RAIR)
Evaluation of rectal prolapse or solitary rectal ulcer syndrome
Patient Preparation
Requires empty rectum (enema is typically required prior to the procedure). Patients should not be on any sedatives or paralytics that could affect sphincter tone or sensation thresholds.
Push (Straining) Phase: Assesses propulsive force and paradoxical anal contraction (Dyssynergia).
04
Sensation: Measures first sensation, desire to defecate, and urgency (Rectal Compliance).
Section 2
Formula & Logic
Physiological Parameters
Anorectal manometry (ARM) uses pressure sensors (typically High-Resolution Solid-State) to map the pressure profile of the anal canal. The London Classification v1.0 (2020) provides standardized definitions for diagnostic groups.
The London Classification (v1.0) Key Groups
01
Disorders of Anal Tone/Contractility: Hypotonia (incontinence) or Hypertonia.
02
Disorders of Rectal Sensation: Hyposensitivity (constipation) or Hypersensitivity.
03
Disorders of Coordination: Dyssynergic Defecation (failed puborectalis relaxation).
04
Disorders of Structure: Rectocele or intussusception (revealed by defecography component).
The RAIR (Rectoanal Inhibitory Reflex)
The RAIR is the reflexive relaxation of the internal anal sphincter (IAS) in response to rectal distention. Its absence is a hallmark of Hirschsprung disease (aganglionosis). If absent, a rectal suction biopsy is the mandatory next step.
Section 3
Pearls/Pitfalls
Dyssynergic Defecation Patterns
Rao et al. classified 4 types: Type 1 (high intra-rectal pressure, paradoxically high anal pressure), Type 2 (low intra-rectal pressure, paradoxically high anal pressure), Type 3 (high intra-rectal pressure, failed anal relaxation), and Type 4 (low intra-rectal pressure, failed anal relaxation).
Biofeedback Utility
Biofeedback is the first-line treatment for Dyssynergic Defecation, with a success rate of 70–80% for correcting manometric abnormalities and improving symptoms — significantly more effective than standard laxative therapy.
Common Pitfalls
Pseudo-dyssynergia — patients may paradoxically contract when an observer is in the room (laboratory environment artifact)
Interpretation for incontinence must always include a Rectal Sensation assessment; "anal weakness" is only half the story
High-Resolution (HR-ARM) is superior to perfusion manometry for mapping the puborectalis "slings"
Section 4
Next Steps
Diagnostic Integration
01
RAIR Absent: Refer for Rectal Suction Biopsy (Screen for Hirschsprung).
The International Anorectal Physiology Working Group (IAPWG) was formed to harmonize the conflicting manometry standards used across Europe and the US. The London Classification was the first to use algorithmic decision trees for diagnosis, mirroring the Chicago Classification for esophageal motility.
