What is the diagnostic approach for fecal incontinence?

Diagnostic Approach for Fecal Incontinence

Begin with a detailed clinical history focusing on the type, frequency, and consistency of stool leakage, followed by digital rectal examination and basic screening tests, then proceed to specialized anorectal physiologic testing only when conservative management fails. 1

Initial Clinical Assessment

Essential History Components

The clinical history must specifically characterize:

• Type of incontinence: Urge incontinence (inability to defer defecation), passive incontinence (unconscious leakage), or combined 1
• Frequency and volume: Number of episodes per week, amount of leakage (staining vs. complete evacuation) 2
• Stool consistency: Liquid, solid, or both—this is critical as diarrhea is the strongest independent risk factor (OR=53) 2, 1
• Presence or absence of rectal urgency: A key predictor of severity 2
• Need for digital manipulation to evacuate stool 2
• Sensation of incomplete evacuation 2

Critical Risk Factor Assessment

Document these specific risk factors that drive diagnostic decisions:

• Bowel disturbances: Diarrhea is by far the most important risk factor, followed by constipation with overflow 2, 1
• Obstetric history: Forceps delivery, complicated episiotomy, anal sphincter trauma 2, 1
• Surgical history: Prior anal surgery, cholecystectomy (OR=4.2), hemorrhoidectomy 2
• Medications: Opiates, anticholinergics, calcium channel blockers that cause constipation with overflow 2
• Comorbidities: Diabetes (peripheral neuropathy), inflammatory bowel disease, neurological disorders 2, 1

Physical Examination

Digital Rectal Examination (Mandatory)

Every patient requires a digital rectal examination—this is a safe, simple diagnostic tool with particular benefit in identifying structural and functional abnormalities 2.

Assess the following systematically:

• Resting sphincter tone: Evaluate internal anal sphincter function 2
• Squeeze pressure: Test external anal sphincter and puborectalis contraction during voluntary squeeze 2
• Simulated defecation: Instruct patient to "expel my finger" to assess pelvic floor coordination 2
• Perineal descent: Observe descent during straining and elevation during squeeze in left lateral position 2
• Anal verge inspection: Look for patulous opening (suggests neurogenic dysfunction), prolapse, fissures, or fecal soiling 2
• Palpable masses or tenderness: Acute tenderness along puborectalis suggests levator ani syndrome 2

Abdominal and Perineal Examination

• Abdominal examination: Assess for distension, masses, liver enlargement 2
• Perineal inspection: Check for skin tags, fissures, prolapse, hemorrhoids 2

Initial Screening Tests

Perform basic blood and stool tests before proceeding to specialized testing 2:

• Complete blood count: Screen for anemia 2
• Metabolic panel: Thyroid-stimulating hormone, glucose, calcium (though diagnostic yield is low) 2
• Fecal calprotectin: Exclude colonic inflammation if inflammatory bowel disease suspected 2
• Stool studies: Culture, ova and parasites if infectious diarrhea suspected 2

Specialized Anorectal Physiologic Testing

Reserve specialized testing for patients who fail conservative management or when surgical intervention is being considered 3, 1. A normal digital rectal examination does not exclude pelvic floor dysfunction 2.

Anorectal Manometry (Primary Specialized Test)

Indicated when:

• Conservative measures (dietary modification, fiber, antidiarrheals, biofeedback) have failed 1
• Surgical intervention is being considered 3
• Objective assessment needed to guide therapy 3

Provides information on:

• Resting and squeeze pressures
• Rectal sensation and compliance
• Rectoanal inhibitory reflex 1

Pudendal Nerve Terminal Motor Latency (PNTML)

This is the most important predictor of surgical outcome—it cannot be assessed by digital examination alone 3:

• Normal PNTML: Sphincteroplasty is an excellent option with 70-90% good-to-excellent results 3
• Prolonged PNTML (neuropathy present): Consider postanal or total pelvic floor repair instead 3

Endoanal Ultrasound

Indicated to:

• Identify anal sphincter defects from obstetric or surgical trauma 1
• Guide surgical planning for sphincteroplasty 3

Additional Specialized Tests (Selected Cases)

• Defecography (fluoroscopic or MR): When structural abnormalities suspected (rectocele, rectal prolapse, intussusception) 3, 1
• Electromyography: Assess pelvic floor muscle function and coordination 3, 4
• Rectal compliance and sensation testing: When overflow incontinence or neurologic dysfunction suspected 1

Imaging for Structural Abnormalities

MR Defecography (Preferred Imaging Modality)

MR defecography with rectal contrast is the initial imaging test of choice when defecatory dysfunction or structural abnormalities are suspected 2:

• Provides direct visualization of pelvic organs, pelvic floor muscles, and fascia 2
• Detects rectoceles, enteroceles, rectal intussusception, and prolapse 2
• Reveals excessive perineal descent in fecal incontinence 2
• Imaging during defecation phase is essential—dynamic straining alone without defecation is insufficient 2

Cystocolpoproctography (Alternative)

• Fluoroscopic technique with sensitivity of 83% for peritoneocele detection 5
• May be used when MR defecography unavailable 2

Common Pitfalls to Avoid

• Do not skip digital rectal examination: Even if it appears normal, specialized testing may still be needed 2
• Do not order specialized testing before attempting conservative management: Most patients respond to dietary modification, fiber, antidiarrheals, and biofeedback 1
• Do not proceed to surgery without pudendal nerve testing: PNTML results determine surgical approach and predict outcomes 3
• Do not assume sphincter defect without imaging: Clinical examination alone misses many structural abnormalities 2

Diagnostic Algorithm Summary

1. Detailed history → Characterize type, severity, risk factors 1
2. Digital rectal examination → Assess sphincter tone, coordination, structural abnormalities 2
3. Basic screening tests → CBC, metabolic panel, stool studies as indicated 2
4. Trial of conservative management → Dietary modification, fiber, antidiarrheals, biofeedback 1
5. If conservative management fails → Anorectal manometry, PNTML, endoanal ultrasound 3, 1
6. If structural abnormalities suspected → MR defecography 2
7. Surgical planning → Use PNTML results to guide procedure selection 3