Workup of Slow Transit Constipation in Outpatient GI Clinic
The diagnostic workup for slow transit constipation should begin with a thorough clinical assessment followed by specific diagnostic tests including colonic transit studies and anorectal function testing to differentiate between slow transit constipation and defecatory disorders. 1
Initial Clinical Assessment
History
- Focus on specific constipation symptoms:
- Stool frequency
- Stool consistency
- Straining during defecation
- Sensation of incomplete evacuation
- Need for manual maneuvers to facilitate defecation
- Duration of symptoms (chronic constipation defined as symptoms persisting >3 months)
Medication Review
- Identify and discontinue medications with constipating effects if feasible 1
- Common culprits: opioids, calcium channel blockers, anticholinergics, antidepressants
Physical Examination
- Digital rectal examination with assessment of:
- Resting anal tone
- Squeeze pressure
- Pelvic floor motion during simulated evacuation
- Ability to "expel examiner's finger"
- Presence of rectocele or other structural abnormalities
- Tenderness along puborectalis (suggesting levator ani syndrome)
Basic Laboratory Testing
- Complete blood count (strong recommendation, low-quality evidence) 1
- Metabolic tests generally not recommended unless clinical features warrant (strong recommendation, moderate-quality evidence):
- Thyroid-stimulating hormone
- Serum glucose
- Calcium
- Creatinine
Structural Evaluation
- Colonoscopy indicated only if:
- Patient has alarm features (blood in stool, anemia, weight loss)
- Age >50 years without previous colorectal cancer screening
- Abrupt onset of constipation symptoms 1
Specialized Testing Algorithm
Step 1: Assess for Defecatory Disorders
- Anorectal manometry to evaluate:
- Resting and squeeze anal pressures
- Rectoanal inhibitory reflex
- Rectal sensation
- Balloon expulsion test
- Defecography (conventional or MR) if anorectal manometry suggests defecatory disorder
Step 2: Evaluate Colonic Transit
- Colonic transit should be evaluated if:
- Anorectal testing does not show defecatory disorder, OR
- Symptoms persist despite treatment of defecatory disorder 1
Transit Testing Options
Radiopaque Marker Study (most widely available):
- Patient ingests capsule containing radiopaque markers
- Abdominal X-ray taken at 5-7 days
- Retention of >20% of markers indicates slow transit 2
Scintigraphic Transit Study:
- More detailed assessment of regional colonic transit
- Requires specialized nuclear medicine facilities 2
Wireless Motility Capsule:
- Provides whole gut and regional transit times
- Non-radioactive alternative 2
Advanced Testing (for Refractory Cases)
- Colonic manometry and barostat testing (available only at specialized centers) 1
- Small bowel transit studies if combined small bowel and colonic dysmotility is suspected 3
Diagnostic Categorization
After completing the evaluation, patients can be categorized into one of the following:
- Normal transit constipation (NTC)
- Slow transit constipation (STC)
- Defecatory disorder
- Combined STC and defecatory disorder
- Secondary constipation (due to organic disease or medication side effect) 1
Common Pitfalls to Avoid
- Failing to perform adequate anorectal function testing before diagnosing isolated STC
- Overlooking defecatory disorders, which may coexist with STC and require different treatment approaches
- Premature referral for surgical intervention without comprehensive physiological assessment
- Not assessing psychological factors that may contribute to symptoms
- Performing extensive testing before an adequate trial of conservative management
By following this systematic approach, clinicians can accurately diagnose slow transit constipation and distinguish it from other causes of constipation, leading to more targeted and effective treatment strategies.