- Indications
- Chronic anal fissure, especially with hypertonic internal sphincter
- Failed conservative management (e.g. topical GTN or diltiazem)
- Contraindications
- Active perianal infection (e.g. abscess)
- Allergy to botulinum toxin
- Neuromuscular disorders (e.g. myasthenia gravis)
- Pregnancy and breastfeeding (relative, depending on agent and dose)
- Mechanism of Action
- Botulinum toxin blocks acetylcholine release at the neuromuscular junction
- Induces temporary paralysis of the internal anal sphincter
- Reduces resting tone → improves blood flow → promotes healing of fissure
- Equipment
- Botulinum toxin (commonly Botox – onabotulinumtoxinA)
- 1 mL syringe with 27–30G needle
- Diluent (usually preservative-free saline)
- Gloves, lubricant, swabs
- Technique
- Preparation of Injection
- Reconstitute Botox (typically 20–40 units in 1–2 mL saline)
- Draw into fine-gauge syringe
- Identify Injection Sites
- Locate internal sphincter by digital rectal exam
- Clean perianal area and apply lubricant as needed
- Inject into Internal Anal Sphincter
- Inject half the dose at 3 o’clock position (left lateral)
- Inject half the dose at 9 o’clock position (right lateral)
- Insert needle into the intersphincteric groove — deep enough to reach internal sphincter, not the mucosa or subcutis
- Inject slowly to reduce pain and leakage
- Post-Procedure Care
- Observe briefly for immediate adverse effects (rare)
- Return to normal activity same day
- Stool softeners and high-fibre diet to aid fissure healing
- Repeat injection may be needed after 8–12 weeks if fissure persists
- Complications
- Minor:
- Mild discomfort at injection site
- Temporary flatus incontinence (up to 10% but usually resolves)
- Local bleeding
- Rare:
- Systemic spread (e.g. weakness — extremely rare at low doses)
- Infection