Indications for Anorectal Manometry
The primary indications for anorectal manometry are fecal incontinence and constipation, particularly when evaluating for dyssynergic defecation and when standard treatments have failed. 1
Primary Indications
1. Fecal Incontinence
Anorectal manometry is essential for evaluating patients with fecal incontinence to:
- Identify anal sphincter weakness
- Assess rectoanal inhibitory reflex
- Evaluate rectal sensory function
- Measure anal canal pressure response to cough
- Determine rectal compliance
Fecal incontinence is the most common indication for anorectal manometry, particularly in patients over 40 years of age, with a 4:1 ratio compared to constipation in those over 60 years old. 2
2. Constipation with Suspected Dyssynergic Defecation
ARM is crucial in the diagnostic workup of refractory constipation to:
- Identify dyssynergic defecation patterns
- Assess rectoanal coordination during simulated defecation
- Evaluate rectal sensory thresholds
- Measure rectal compliance
- Guide biofeedback therapy decisions
ARM provides objective evidence of dyssynergic defecation, which is found in approximately 43% of constipated patients. 3
Additional Indications
3. Anorectal Pain
ARM can help evaluate patients with chronic anorectal pain by:
- Identifying abnormal pressure patterns
- Assessing for pelvic floor dysfunction
- Evaluating rectal hypersensitivity
4. Pre-surgical Assessment
ARM is valuable when evaluating surgical options for:
- Rectal cancer
- Inflammatory bowel disease
- Planning reanastomosis after colonic diversion
- Assessing sphincter function before restoring colorectal anatomy 1
5. Pediatric Applications
In children, ARM is particularly useful for:
- Differentiating Hirschsprung disease from functional constipation
- Evaluating congenital anorectal anomalies 2
Clinical Utility and Testing Components
The comprehensive ARM assessment typically includes:
- Resting anal canal pressure
- Anal canal squeeze pressure (peak and duration)
- Rectoanal inhibitory reflex
- Anal canal pressure response to cough
- Anal canal pressure during defecatory maneuvers
- Simulated defecation with balloon or contrast
- Rectal compliance measurement
- Sensory thresholds assessment 4
Important Considerations
- ARM results should be interpreted with reference to age- and sex-matched normal values
- The rectal balloon expulsion test should be performed alongside ARM for more comprehensive evaluation
- ARM findings should be correlated with clinical symptoms and other test results 5
- ARM can identify which patients are likely to benefit from biofeedback therapy 1
Pitfalls and Limitations
- Lack of standardized protocols and normative data
- Variable day-to-day reproducibility, especially during simulated evacuation
- Limited sensitivity and specificity for certain parameters
- Patients may compensate for physiological deficits through other mechanisms 4
- Symptoms alone (e.g., straining, incomplete evacuation) are poor predictors of underlying pathophysiology 1
ARM technology has evolved significantly, with high-resolution and 3D systems now available that provide more detailed assessment of anorectal function compared to traditional water-perfused systems. These advanced systems offer better visualization and understanding of complex pressure patterns in the anorectum. 6