How does a lateral internal sphincterectomy affect anal sexual functions versus continence in a patient with a history of anorectal procedures?

Lateral Internal Sphincterotomy: Impact on Anal Sexual Function vs Continence

Lateral internal sphincterotomy (LIS) carries a substantial risk of fecal incontinence—affecting up to 45% of patients at some point postoperatively—with women experiencing significantly higher rates (53.4%) than men (33.3%), though most episodes are minor and transient, with only 3% reporting long-term quality of life impact. 1

Understanding the Dual Impact

Continence Effects

The continence complications from LIS are well-documented and occur through direct sphincter division:

• Immediate postoperative period: Incontinence manifests as flatus incontinence (31%), mild soiling (39%), or gross incontinence (23%) at some point after surgery 1
• Long-term outcomes (>5 years): Only 6% report flatus incontinence, 8% have minor soiling, and 1% experience solid stool loss 1
• Gender disparity: Women experience incontinence at 1.6 times the rate of men (53.4% vs 33.3%, p<0.05) 1
• Quality of life: Despite high incidence rates, only 3% of patients report that incontinence ever affected their quality of life 1

Sexual Function Effects

The impact on anal sexual function operates through a different mechanism than mechanical incontinence:

• Neuropathic dysesthesia: The World Journal of Emergency Surgery identifies altered sensations and sexual dysfunction following LIS as primarily neuropathic pain and dysesthesia rather than structural sphincter damage 2
• Preserved sphincter integrity: Patients with sexual dysfunction typically have intact continence and altered sensations rather than mechanical problems 2
• Myofascial component: Pelvic floor muscle tension commonly develops after anorectal surgery and contributes to altered sensations during sexual activity 2

Critical Technical Factors Affecting Both Outcomes

Extent of Sphincter Division

The proportion of internal sphincter divided is the single most important modifiable factor determining both continence and sexual function outcomes:

• Safe threshold in women: Division of less than 25% of total sphincter length (corresponding to <1 cm) maintains continence scores of 0 in significantly more patients compared to ≥25% division 3
• Calibrated approach: Tailoring sphincter division to manometry results—20% for mild hypertonia (50-60 mmHg), 40% for moderate (60-80 mmHg), and 60% for severe (>80 mmHg)—achieves 97.6% cure rates with only 0.4% gas incontinence 4
• Segmental technique: Dividing the sphincter in two segments at different planes resulted in zero transient or persistent incontinence in a 50-patient series 5

Treatment Algorithm for Post-LIS Sexual Dysfunction

When sexual dysfunction develops after LIS with preserved continence:

First-Line Conservative Management (6-12 months)

• Specialized pelvic floor physical therapy: 2-3 times weekly focusing on internal and external myofascial release 2
• Topical lidocaine 5% ointment: Applied to affected areas for neuropathic pain management 2
• Gradual desensitization exercises: Guided by physical therapist 2
• Warm sitz baths: To promote muscle relaxation 2
• Muscle coordination retraining: To reduce protective guarding patterns that developed during the painful fissure period 2

Expected Timeline

• Improvement trajectory: Dysesthesia and altered sensations typically improve significantly over 6-12 months with appropriate pelvic floor therapy and neuropathic pain management 2
• Favorable prognostic indicator: Absence of incontinence or structural damage suggests better potential for improvement with conservative management 2

Alternative to LIS: Botulinum Toxin

For patients concerned about either continence or sexual function risks, botulinum toxin injection represents the safest alternative, achieving 75-95% cure rates with no risk of permanent incontinence or sexual dysfunction. 6, 7

• Mechanism: Causes temporary (3-month) paresis of anal sphincter, reducing resting tone and allowing fissure healing through reversible sphincter relaxation without permanent damage 7
• Efficacy: Comparable cure rates to LIS but with zero risk of permanent sphincter damage 6, 7
• Timing: Should be considered after 8 weeks of failed topical therapy (calcium channel blockers first-line, nitroglycerin second-line) 6, 7

Critical Pitfalls to Avoid

• Do not pursue additional surgical interventions for post-LIS sexual dysfunction, as this would likely worsen the neuropathic component 2
• Avoid manual anal dilatation entirely: Carries 30% temporary and 10% permanent incontinence rates 8
• Do not divide >25% of sphincter length in women without accepting significantly increased incontinence risk 3
• Recognize the distinction: Sexual dysfunction after LIS is typically neuropathic/myofascial rather than mechanical sphincter failure, requiring physical therapy rather than surgical revision 2

Comparative Risk-Benefit Analysis

LIS remains the gold standard for chronic anal fissure with technical simplicity, minimal morbidity, rapid symptom relief, >90% healing rates, and low relapse rates 6. However, the 45% overall incontinence rate (though mostly transient) and potential for sexual dysfunction must be weighed against the zero permanent damage risk of botulinum toxin 6, 1. For patients with risk factors for incontinence, compromised sphincter function, or concerns about sexual function, botulinum toxin should be strongly preferred 6, 7.