Piriformis muscle syndrome is a painful disorder characterized by buttock and hip pain usually due to sciatic nerve compression. Some previous works have studied the efficacy and safety of botulinum toxin in the management of piriformis muscle syndrome. Our objectives are analyze the efficacy of ultrasound-guided injections of incobotulinumtoxinA (Xeomin®) in the reduction of pain in piriformis muscle syndrome, and study if there are differences in the efficacy related with the dilution volume.

A retrospective cohort including patients admitted to Rehabilitation Department from January 1st 2015 to June 30th 2016 was analyzed. 58 patients who fulfilled the required criteria were registered. In all the included patients, Visual Analogical Scale (VAS) was measured before performing a ultrasound-guided injection of 100 units of incobotulinumtoxinA in piriformis muscle, and 6 weeks after the injection. All the injections were performed by the same investigator. All the injections were performed using volume dilutions of 50 U/mL (n=18), 20U/mL (n=19) or 10 U/mL (n=21).

After performing Kolmogorov–Smirnov test, we checked that the data did not follow a normal distribution so a non-parametric test (Wilcoxon signed-rank test) was used. There was a statistically significant reduction of pain 6 weeks after incobotulinumtoxinA injection (Z_W=−6.649, P<0.01). All dilutions showed statistically significant reduction of pain: (10U/mL: Z_W=−4.027, P<0.01; 20 U/mL: Z_W=−3.837, P<0.01; 50 U/mL: Z_W=−3.753, P<0.01).

IncobotulinumtoxinA seems to be a useful therapy in the management of piriformis muscle syndrome. There are no differences in the efficacy related with the volume of dilution.