What functional pelvic‑floor disorder causes sharp left‑sided rectal pain with straining, and how should it be diagnosed and treated?

Sharp Left-Sided Rectal Pain with Straining: Pelvic Floor Dyssynergia

This presentation is most consistent with a functional defecatory disorder, specifically pelvic floor dyssynergia (also called anismus or dyssynergic defecation), which causes sharp rectal pain during straining due to paradoxical contraction or incomplete relaxation of the pelvic floor muscles during attempted defecation. 1

Understanding the Disorder

Pelvic floor dyssynergia is characterized by impaired rectal evacuation from inadequate rectal propulsive forces and/or increased resistance to evacuation. 1 The sharp left-sided rectal pain your patient experiences during straining to pass gas or have a bowel movement is a hallmark feature of this condition. 1

Key Clinical Features to Assess

The following symptoms strongly suggest a defecatory disorder rather than other functional motility problems: 1

• Excessive straining even with soft stool
• Sense of anorectal blockage during defecation
• Need for manual maneuvers during defecation (digital disimpaction or splinting)
• Feeling of incomplete evacuation 1
• Pain specifically triggered by straining rather than constant pain 1

A critical distinction: If the pain were brief (lasting seconds to minutes) and episodic without relation to defecation, proctalgia fugax would be considered. 2 However, your patient's pain is directly linked to straining, which points to dyssynergia. 1

Diagnostic Approach

Initial Clinical Evaluation

Begin with a detailed history focusing on the specific characteristics of the pain and defecation pattern. 1 Ask specifically about:

• Whether straining occurs throughout the entire evacuation or just at initiation 1
• Need for digital assistance or positional changes 1
• Duration of symptoms (chronic vs. acute) 1
• Presence of psychological disturbances (common in one-third of functional anorectal pain patients) 3

Physical Examination

A digital rectal examination is essential and should assess: 1

• Resting anal sphincter tone (may be elevated in dyssynergia) 1, 4
• Sphincter tone augmentation with squeeze 4
• Puborectalis muscle contraction during squeeze 4
• Localized tenderness along the puborectalis (suggests levator ani syndrome if present) 4
• Ability to relax pelvic floor during simulated defecation (impaired in dyssynergia) 4
• Patient's ability to "expel the examiner's finger" (reduced in dyssynergia) 4

Important caveat: A normal digital rectal examination does NOT exclude pelvic floor dysfunction. 4 Many patients with dyssynergia will have subtle findings that require physiologic testing to confirm. 1

Confirmatory Testing

After initial evaluation, if symptoms persist despite conservative measures, anorectal physiology testing is strongly recommended. 1

The diagnosis of pelvic floor dyssynergia should be confirmed by anorectal physiology testing combined with balloon expulsion test. 1 These tests demonstrate:

• Paradoxical contraction or incomplete relaxation of anal sphincters during attempted defecation 1
• Inability to expel a balloon from the rectum 1
• Abnormal anorectal angle changes during straining 1

MR defecography can be considered if: 1

• There is concern for structural abnormalities (rectocele, intussusception, enterocele) 1
• The patient has rectal pain suggesting possible structural causes 1
• Initial testing is inconclusive but clinical suspicion remains high 1

MR defecography findings in dyssynergia include impaired evacuation, abnormal anorectal angle change, and paradoxical sphincter contraction. 1

Treatment Algorithm

First-Line Treatment: Pelvic Floor Retraining

Biofeedback therapy (pelvic floor retraining) rather than laxatives is the recommended treatment for defecatory disorders. 1 This is a strong recommendation with high-quality evidence. 1

Biofeedback is particularly effective in patients with functional anorectal pain who have difficulty with defecation. 3 In one study, 17 of 29 patients (59%) improved with biofeedback, making it the most effective intervention. 3

The mechanism works by:

• Training patients to relax pelvic floor muscles during straining 1
• Restoring normal rectoanal coordination 1
• Suppressing the nonrelaxing pelvic floor pattern 1

Success depends on: 1

• Patient motivation
• Therapist expertise
• Frequency and intensity of the retraining program
• Involvement of behavioral psychologists when needed 1

Second-Line Options for Refractory Cases

If biofeedback fails or is unavailable, consider: 3

1. Tricyclic antidepressants: 10 of 26 patients (38%) improved 3
2. Botulinum toxin injection: 5 of 9 patients (56%) improved 3
3. Sacral nerve stimulation: 2 of 3 patients (67%) improved, though limited data 3

Important limitation: Outside of clinical trials, botulinum toxin injection cannot be broadly recommended based on current evidence. 1

Common Pitfalls to Avoid

1. Treating with laxatives alone: Laxatives are ineffective for dyssynergia and may worsen symptoms by increasing straining. 1

2. Assuming IBS: While functional anorectal pain can overlap with IBS features, the key distinguishing factor is that dyssynergia pain is specifically triggered by defecation/straining, not by eating or generalized bowel habit changes. 1

3. Skipping anorectal testing: Clinical history alone is insufficient; physiologic confirmation changes management. 1

4. Ignoring psychological comorbidities: One-third of patients with functional anorectal pain have psychological disturbances that require concurrent management. 3

5. Pursuing surgery prematurely: Surgical options are limited and should only be considered after adequate trial of biofeedback therapy. 1

When to Suspect Alternative Diagnoses

Consider other causes if: 1

• Pain is constant and unrelated to defecation (suggests functional abdominal pain syndrome) 5
• Pain is brief (seconds to minutes) and episodic without defecation trigger (proctalgia fugax) 2
• Structural abnormalities are found on examination (anal fissure, proctitis, stricture) 1
• Red flag symptoms are present (fever, weight loss, blood in stool, anemia) 1

The left-sided location of pain may suggest: 6

• Abdominal wall pain if reproducible with muscle contraction 6
• Levator ani syndrome if there is localized tenderness on palpation 4

However, the clear association with straining during defecation makes pelvic floor dyssynergia the most likely diagnosis. 1