After a lateral internal sphincterotomy I have loss of internal anal sphincter resting tone causing absent rectal sensation for sexual arousal and altered urinary function; how should I evaluate and manage this hypo‑tone?

Post-Lateral Internal Sphincterotomy Hypotonia: Evaluation and Management

Your symptoms of decreased internal anal sphincter resting tone with loss of rectal sensation and altered urinary function after lateral internal sphincterotomy require urgent neurological evaluation to exclude cauda equina syndrome, followed by conservative management with pelvic floor physical therapy if neurological causes are ruled out.

Immediate Neurological Evaluation Required

You must first exclude cauda equina syndrome (CES), which presents with loss of perineal sensation, altered urinary function, and decreased anal tone—exactly matching your symptom complex 1:

• Emergency MRI of the lumbosacral spine is mandatory when a patient presents with the triad of impaired perineal sensation, altered bladder function, and decreased anal tone 1
• The combination of altered urinary function with loss of rectal sensation represents "red flag" features that require imaging within hours, not days 1
• While your symptoms followed surgery, the temporal relationship does not exclude concurrent neurological pathology that may have been unmasked or coincidentally developed 1

Critical distinction: CES causes hypotonia from nerve root compression, whereas your surgery was intended to reduce hypertonia. The fact that you now have hypotonia with sensory changes and urinary symptoms makes neurological evaluation non-negotiable 1.

Understanding What Likely Happened During Your Surgery

Lateral internal sphincterotomy predictably reduces resting anal pressure, but the extent matters 2:

• Normal post-sphincterotomy pressure drops from approximately 138 mmHg to 86 mmHg at one month, then gradually recovers to 110 mmHg by 12 months 2
• Even at 12 months, pressures remain significantly lower than pre-operative baseline but higher than normal controls (110 mmHg vs 73 mmHg) 2
• Excessive sphincterotomy length (>75% of the sphincter) directly correlates with incontinence and likely correlates with your sensory symptoms 3

The loss of baseline rectal pressure sensation you describe suggests either an excessively long sphincterotomy or concurrent external sphincter injury 3.

Diagnostic Workup After Neurological Clearance

Once CES is excluded by MRI, proceed with anorectal evaluation 4:

• Anorectal manometry to quantify current resting pressure, squeeze pressure, and rectal sensation thresholds 4
• 3D anal ultrasonography to measure the exact length and width of your internal sphincter defect and assess external sphincter integrity 4, 3
• Document whether the sphincterotomy extends >75% of the sphincter length, as this predicts permanent dysfunction 3
• Measure external sphincter thickness, as thinning (<7 mm) indicates concurrent injury contributing to your symptoms 3

Conservative Management Protocol

Do not pursue any additional surgical intervention—this would worsen neuropathic symptoms rather than improve them 5, 6:

Pelvic Floor Physical Therapy (Primary Treatment)

• Initiate 2-3 sessions weekly with a therapist experienced in post-surgical anorectal dysfunction 5
• Treatment components include internal and external myofascial release, gradual desensitization exercises, and muscle coordination retraining 5
• Protective guarding patterns that developed during your painful fissure period persist after surgery and require specific retraining 5, 6
• Warm sitz baths 2-3 times daily to reduce pelvic floor muscle tension 5

Neuropathic Pain Management

• Topical lidocaine 5% ointment applied to affected perineal areas for dysesthesia and altered sensation 5
• This addresses the neuropathic component of your sensory changes 5

Expected Timeline

• Significant improvement in dysesthesia and altered sensations typically occurs over 6-12 months with consistent pelvic floor therapy 5
• Manometric studies show continued gradual recovery of internal sphincter tone throughout the first year post-surgery 2

Addressing Your Specific Concerns

Loss of Rectal Sensation for Arousal

The internal anal sphincter is anatomically distinct from deep pelvic autonomic nerves and is confined to the anal canal level 6. Your sexual dysfunction likely results from:

• Altered sensory feedback from excessive sphincter division 3
• Pelvic floor muscle tension and protective guarding affecting the entire pelvic floor, not just the anal sphincter 5, 6
• Neuropathic changes in the surgical area 5

Pelvic floor physical therapy specifically addresses these mechanisms and should improve sexual function as pelvic floor coordination normalizes 5.

Altered Urination

While the internal anal sphincter does not directly control urinary function 6, your urinary symptoms may reflect:

• Generalized pelvic floor dysfunction from protective guarding 5, 6
• Concurrent neurological pathology (hence the mandatory MRI) 1
• Pelvic floor muscle incoordination affecting both anorectal and urinary sphincter mechanisms 4

Critical Pitfalls to Avoid

• Never undergo manual anal dilatation—this causes permanent incontinence in 10-30% of patients and would devastate your already compromised sphincter 6, 4
• Do not pursue revision sphincterotomy or sphincter repair at this stage—surgical intervention worsens neuropathic symptoms 5
• Do not accept reassurance without imaging—your symptom complex mandates MRI to exclude CES 1

Long-Term Prognosis

Most patients with post-sphincterotomy sensory changes improve significantly with conservative management 5. However, you should understand:

• 45% of patients experience some degree of incontinence after lateral internal sphincterotomy, though most episodes are minor and transient 7
• By 5+ years post-surgery, only 3% report that incontinence affects quality of life 7
• Your sensory symptoms are less commonly reported but follow similar recovery patterns to incontinence when managed with pelvic floor therapy 5

What Should Have Been Done Differently

For future reference, botulinum toxin injection achieves 75-95% cure rates for anal fissure with no risk of permanent incontinence or sexual dysfunction, representing a safer alternative to sphincterotomy 5, 6.