In a patient with sensation of incomplete bowel evacuation, normal colonoscopy and abdominal ultrasound, and an enlarged prostate treated with tamsulosin 0.4 mg daily, what is the most likely diagnosis and appropriate first‑line management?

Likely Diagnosis and Management

This patient most likely has a defecatory disorder (dyssynergic defecation) causing the sensation of incomplete bowel evacuation, and the first-line management is anorectal manometry with balloon expulsion testing followed by biofeedback therapy if dyssynergia is confirmed. 1

Clinical Reasoning

The presentation of incomplete bowel evacuation with normal colonoscopy strongly suggests a functional defecatory disorder rather than structural pathology. The key diagnostic clues are:

• Sensation of incomplete evacuation is a hallmark symptom of defecatory disorders, particularly when structural causes have been excluded by colonoscopy 2, 1
• The enlarged prostate and urinary symptoms are relevant because pelvic floor dysfunction commonly affects both urinary and defecatory function simultaneously 2
• Normal colonoscopy and ultrasound effectively exclude structural causes such as colorectal cancer, strictures, or mechanical obstruction 2, 1

Diagnostic Approach

Digital Rectal Examination (Critical First Step)

Perform a focused digital rectal examination to assess:

• Resting tone of the internal anal sphincter and augmentation during voluntary squeeze 1
• Puborectalis muscle contraction during squeeze maneuver 1
• Pelvic floor motion during simulated defecation (asking the patient to "bear down as if having a bowel movement") 1
• Paradoxical contraction or inadequate relaxation of the pelvic floor during straining strongly suggests dyssynergic defecation 1, 3

Anorectal Testing (Definitive Diagnosis)

Anorectal manometry and balloon expulsion test should be performed first, before any additional colonic transit studies 1, 4:

• These tests identify defecatory disorders with high accuracy by measuring rectoanal coordination and the ability to expel a balloon 2, 4
• Dyssynergic defecation is characterized by inadequate rectal propulsive forces and/or paradoxical contraction or incomplete relaxation of the pelvic floor and external anal sphincter during attempted defecation 3, 4
• Colonic transit studies should only be performed if anorectal testing is normal or symptoms persist despite treatment of confirmed dyssynergia 1

First-Line Treatment

Biofeedback Therapy (Definitive Treatment)

If dyssynergic defecation is confirmed on anorectal testing, biofeedback therapy is the first-line definitive treatment with strong evidence supporting its efficacy 1, 4, 5:

• Success rates exceed 70% for dyssynergic defecation 1
• Biofeedback trains patients to relax pelvic floor muscles during straining and restores normal rectoanal coordination 1, 5
• This is superior to laxatives or fiber supplementation for defecatory disorders 5

Conservative Measures (Adjunctive)

While awaiting anorectal testing or biofeedback:

• Discontinue or minimize constipating medications if feasible 1
• Increase dietary fiber and fluid intake to optimize stool consistency 1
• Encourage regular physical activity 1

Relationship to Prostate Enlargement

The enlarged prostate and tamsulosin use are relevant but not causative:

• Tamsulosin treats lower urinary tract symptoms from benign prostatic hyperplasia by relaxing smooth muscle in the prostate and bladder neck 6, 7, 8
• Pelvic floor dysfunction commonly affects both urinary and bowel function due to shared neuromuscular pathways 2
• The sensation of incomplete emptying in both bladder and bowel suggests a common underlying pelvic floor dyssynergia 2, 1
• Tamsulosin does not cause constipation and should be continued for urinary symptoms 6, 7

Common Pitfalls to Avoid

• Do not perform colonoscopy repeatedly when the initial study is normal and there are no alarm features (blood in stool, anemia, weight loss, sudden onset) 2, 1
• Do not order colonic transit studies before anorectal testing in patients with symptoms suggesting defecatory disorder 1
• Do not treat empirically with laxatives alone when defecatory disorder is suspected, as this will not address the underlying pelvic floor dyssynergia 5
• Do not attribute bowel symptoms solely to irritable bowel syndrome without excluding defecatory disorders, as up to one-third of chronically constipated patients have an evacuation disorder 4, 5
• Do not assume the prostate enlargement is causing the bowel symptoms, though pelvic floor dysfunction may affect both systems 2, 1

When to Refer

Refer to gastroenterology or a pelvic floor specialist for:

• Anorectal manometry and balloon expulsion testing to confirm dyssynergic defecation 1, 4
• Biofeedback therapy if dyssynergia is confirmed 1, 4
• Persistent symptoms despite conservative measures after 1-2 weeks 1