Lateral internal sphincterotomy, the most common treatment for chronic anal fissure, may cause permanent injury to the anal sphincter, which can lead to fecal incontinence. We compared two nonsurgical treatments that avert the risk of fecal incontinence. We randomly assigned 50 adults with symptomatic chronic posterior anal fissures to receive treatment with either a total of 20 U of botulinum toxin injected into the internal anal sphincter on each side of the anterior midline or 0.2 percent nitroglycerin ointment applied twice daily for six weeks.

Chronic anal fissure is a tear in the lower half of the anal canal that is maintained by contraction of the internal anal sphincter. Sphincterotomy, the most widely used treatment, is a surgical procedure that permanently weakens the internal sphincter and may lead to anal deformity and incontinence.

To investigate the effects of two different dosage regimens of botulinum toxin to induce healing in patients with idiopathic anal fissure. Chronic anal fissure is maintained by contraction of the internal anal sphincter. Sphincterotomy, which is successful in 85% to 95% of patients, permanently weakens the sphincter and therefore might be associated with anal deformity and incontinence. Fifty-seven consecutive outpatients were evaluated. Type A botulinum toxin was injected into the internal anal sphincter. Patients were divided into two treatment groups based on the number of botulinum toxin units injected. Patients in the first group were treated with 15 units and retreated with 20 units. Patients in the second group were treated with 20 units and retreated with 25 units. Two months after treatment, 10 patients in the first group and 23 patients in the second group had a healing scar. Symptomatic improvement was observed in 13 patients in the first group and in 24 patients in the second group. Statistical analysis showed that resting anal pressure varied from baseline values as a function of treatment; in contrast, the treatment had no effect on maximum voluntary pressure. Long-term healing was achieved in 13 patients in the first group and in all patients in the second group who underwent a complete treatment. Botulinum toxin is safe and effective in the treatment of anal fissure. It is less expensive and easier to perform than surgical treatment. No adverse effects resulted from injections of the toxin. The higher dosage is effective in producing long-term healing without complications.