What is the role of Botox (botulinum toxin) injection therapy in the treatment of chronic anal fissures?

Botox Injection Therapy for Chronic Anal Fissure

Botulinum toxin injection is an effective second-line treatment for chronic anal fissures that fail 8 weeks of conservative and topical therapy, achieving 75-95% healing rates with no risk of permanent incontinence, making it the preferred option before considering surgery. 1

Treatment Algorithm: When to Use Botox

Step 1: Exhaust Conservative Management First (2 weeks)

• Start all patients with fiber supplementation, adequate fluid intake, warm sitz baths, and topical analgesics, as approximately 50% of fissures heal with these measures alone 1
• Do not use botulinum toxin as first-line treatment 1

Step 2: Topical Pharmacotherapy (6-8 weeks)

• If conservative measures fail after 2 weeks, advance to topical calcium channel blockers (0.3% nifedipine with 1.5% lidocaine) applied three times daily for at least 6 weeks, which achieve 65-95% healing rates 2
• Nitroglycerin ointment is second-line with lower healing rates of 25-50% and more headache side effects 1

Step 3: Botulinum Toxin Injection (After 8 weeks of failed non-operative management)

• Reserve botulinum toxin for fissures that remain unhealed after 8 weeks of comprehensive conservative and topical therapy 1, 2
• This timing defines the transition from acute to chronic fissure requiring more aggressive intervention 2

Efficacy Data: What to Expect

Healing Rates

• Single injection achieves 73.8% complete healing at 2 months 3
• A second injection (if needed at 2 months) increases overall healing to 86.9% at 6 months 3
• Long-term healing rates stabilize at 75-79% at one year 4, 3
• Pain relief occurs rapidly, with 78-82% of patients pain-free within the first week 5, 4

Comparison to Surgery

• Lateral internal sphincterotomy achieves higher early healing rates (98% at 2 months vs. 73.8% for single Botox injection) and superior one-year healing (94% vs. 75.4%) 3
• However, sphincterotomy carries an 8-16% risk of fecal incontinence that may be permanent, while botulinum toxin causes only transitory incontinence in 4-7% of cases 5, 4, 3
• The critical advantage of botulinum toxin is zero risk of permanent incontinence 1, 4

Technical Considerations

Dosing

• Use 20-40 units total, injected in divided doses 5
• The 20-unit dose is sufficient and equally effective as higher doses 5
• Specifically, 2.5-5 units of Botox injected bilaterally lateral to the fissure 4

Mechanism and Duration

• Botulinum toxin causes temporary paresis of the internal anal sphincter for approximately 3 months, reducing resting anal tone and allowing fissure healing through reversible sphincter relaxation 1, 4
• This addresses the underlying sphincter hypertonia without permanent structural damage 4

Injection Location Controversy

• The optimal injection site (internal vs. external sphincter) remains controversial and unstudied 6, 1
• Most published studies inject bilaterally lateral to the fissure into the internal sphincter 4

Special Populations: Who Benefits Most

• Patients with compromised sphincter function or risk factors for incontinence should strongly consider botulinum toxin over surgery 1
• Women with anterior fissures, who comprise 30% of female fissure patients, are good candidates given their higher baseline incontinence risk 7

Enhanced Technique: Fissurectomy Plus Botox

• For fissures resistant to both topical therapy and initial botulinum toxin injection, combining fissurectomy (excision of fibrotic edges and sentinel pile) with 25 units of botulinum toxin achieves 93% healing 8
• This combination addresses both the sphincter spasm and the chronic fibrotic tissue that prevents healing 8
• Standard fissurectomy alone with botulinum toxin injection increases efficiency from 81.1% to 90.1% compared to fissurectomy without toxin 7

Side Effects and Safety Profile

• Transient flatus or fecal incontinence occurs in 4-7% of patients but resolves completely 5, 4, 7
• No permanent incontinence has been reported in any published series 5, 4
• The procedure is well-tolerated and performed on an outpatient basis 5, 4
• Return to daily activities occurs significantly faster than surgery (1 day vs. 14.8 days) 3

Managing Treatment Failures and Relapses

• If the fissure is not healed at 2 months, repeat the injection once 3
• Relapse rates range from 3-11% within the first 6-12 months 4, 3
• For persistent failures after two injections, consider fissurectomy-botulinum toxin combination or proceed to lateral internal sphincterotomy 8
• Do not rush to surgery for recurrent fissures; repeat the conservative approach first 1

Critical Pitfalls to Avoid

• Never use manual dilatation—it causes high rates of permanent incontinence 1, 2
• Do not skip the 8-week trial of conservative and topical therapy before botulinum toxin 1
• Do not assume all fissures are benign—atypical features (lateral location, multiple fissures, failure to heal) require evaluation for Crohn's disease, inflammatory bowel disease, or malignancy 2
• Avoid using botulinum toxin in acute fissures that have not failed conservative management 2