FLUOROSCOPIC AND ELECTROMYOGRAPHIC GUIDED INJECTION OF THE PIRIFORMIS MUSCLE WITH BOTULINUM TOXIN TYPE B

Paul V. Beck, BS 1 , Gagan Mahajan, MD 1 , Barth L. Wilsey, MD 1,2 , Paul G. Kreis, MD 1 , and Scott M. Fishman, MD 1 Analgesic Research Program: 1 Division of Pain Medicine, University of California, Davis 2 Northern California Veterans Administration Pain Clinics Piriformis syndrome (PS) is possibly an under‐diagnosed form of buttock and leg pain involving irritability of the sciatic nerves, presumably related to effects from the overlapping piriformis muscle. Spasm, inflammation, and hypertrophy of the muscle may compress the sciatic nerve, either between the muscle and the bony pelvis, or between inflamed fascicles of the muscle itself (Durrani and Winnie, 1991.) Injection of the muscle can be difficult. We have developed a novel technique for needle guidance (Fishman et al 1999). Using an injectable 4–6 inch EMG needle, we use EMG to locate the muscle immediately posterior to the ischium followed by fluoroscopy with radiopaque dye injection to confirm needle placement in the piriformis muscle. This technique can be used to deliver therapeutic drugs such as local anesthetics and corticosteroids. Since piriformis spasm is a proposed mechanism for PS and recent reports have indicated superior efficacy for botulinum toxin injection over corticosteroid in certain forms of myofascial pain including PS (Porta, 2000), we have designed a test of botulinum toxin in PS. Several botulinum neurotoxins have been isolated, but until recently, only botulinum toxin type A (BOTOX™) has been available for this indication. Botulinum toxin type B (MYOBLOC™) is now available for clinical uses. Since botulinum toxin type B offers greater stability and ease of use (requires no re‐constitution, stable at room temperature, stable with shaking/turbulence during injections etc), we chose it as the active agent in this trial of 10 patients. We use a randomized placebo controlled enriched enrollment model. Patients are required to have been diagnosed with PS by standard diagnostic criteria as well as have had temporary relief from previous fluoroscopy guided piriformis injection with local anesthetics with corticosteroid. Five patients are randomized to receive the placebo arm and five to receive the active Botulinum Toxin Type B. Data collection is ongoing and will be reported.