Dysport® for the treatment of myofascial back pain: Results from an open-label, Phase II, randomized, multicenter, dose-ranging study.

Background and purpose Botulinum toxin type A (BoNT-A) has antinociceptive and muscle-relaxant properties. The objectives of this study were to investigate the efficacy and safety of a single BoNT-A (Dysport®) treatment in myofascial back pain. Methods In this randomized, open-label, multicenter study, adults with myofascial lower back pain received Dysport® injections at four trigger points (60,80 or 120 units per injection point). Patients were followed for 12 weeks. The a priori primary endpoint was a pooled evaluation, at Week 6, of seven measures of efficacy, including pain intensity (patient diary), modified Pain Disability Index (PDI) score, use of interfering concomitant analgesics, and patient-rated global efficacy. Optional assessments of pressure thresholds and tissue compliance were conducted. Safety was also assessed. Results A total of 202 patients were randomized to treatment and 189 patients received a low (n = 57), medium (n = 57), or high (n = 75) total dose of Dysport® at 34 centers in Germany between October 2002 and October 2003. All treated patients were included in the safety population; 8 patients were excluded from the intention-to-treat population. Patients had moderate to severe pain at baseline. At baseline, 120 patients were receiving concomitant analgesic therapy; 6.7%, 74.2% and 19.2% were considered to cause mild, moderate and severe interference with pain measurements, respectively. There was no difference between doses for the a priori combined primary endpoint. Patient-reported pain intensity scores at rest and on movement decreased significantly after treatment for all groups combined (p < 0.0001 at all visits). At Week 6, reductions in pain intensity at rest were 29%, 19% and 26% for the low-, medium- and high-dose groups, respectively; reductions in pain intensity on movement were 27%, 18% and 26%, respectively. Overall, patients who reported pain intensity reductions at Week 6 were evident within 3 weeks of treatment and were maintained for the 12 weeks of the study. In the total population, significant decreases in mean PDI sum scores from baseline were observed from Week 3 and were maintained through to the end of treatment (Week 12); no differences between the dose groups were observed. Pressure thresholds and tissue compliance also increased during the study. Adverse events were generally as expected for BoNT-A; the majority were mild or moderate in severity. Conclusions Dysport® treatment was associated with reductions in myofascial back pain and was well tolerated. Nodose-response relationship was observed; treatment with Dysport® using a four-trigger-point injection protocol at 60 units per trigger point was associated with a clinically relevant and statistically significant improvement in pain and pain-related disability; there was no additional benefit from the higher doses. Implications Our findings are limited by the lack of a control group and further research is warranted to confirm the value of Dysport® for the treatment of myofascial back pain and confirm the optimum dosing in this indication.