Background: Chronic anal fissure (CAF) is a linear split of the anoderm. The minimally invasive management of CAF such as botulinum toxin (BT) injection is recommended. However, the exact efficient dose of BT, number of injections per session and the injection sites are still debatable. The aim of this analysis was to assess the dose-dependent efficiency of botulinum toxin injection for CAF.
Methods: PubMed and Web of Science databases were searched for terms: "anal fissure" AND "botulinum toxin." Studies published between October 1993 and May 2015 were included and had to meet the following criteria: (1) chronic anal fissure, (2) prospective character of the study, (3) used simple BT injection without any other interventions and (4) no previous treatment with BT.
Results: A total of 1577 patients from 34 prospective studies used either Botox or Dysport formulations were qualified for this meta-analysis. A total number of BT units per session ranged from 5 to 150 IU, whereas the efficiency across analyzed studies ranged from 33 to 96 %. Surprisingly, we did not observe a dose-dependent efficiency (Spearman's rank correlation coefficient, ρ = 0.060; p = 0.0708). Moreover, there were no BT dose-dependent postoperative complications or fecal incontinence and significant difference in healing rates compared BT injection into the anal sphincter muscles.
Conclusions: BT injection has been an accepted method for the management of CAF. Surprisingly, there is no dose-dependent efficiency, and the postoperative incontinence rate is not related to the BT dosage regardless the type of formulation of botulinum neurotoxin used. Moreover, no difference in healing rate has been observed in regard to the site and number of injections per session.