Effects of intra-articular botulinum toxin type A in an equine model of acute synovitis: a pilot study

To test the hypothesis that botulinum toxin type A (BoNT-A) can attenuate lameness associated with acute synovitis in an equine model.

Four horses 2-6 yrs of age with clinically normal carpi were studied for 15 days. Kinematic gait analysis and clinical measures of lameness were conducted before and after experimental interventions. Horses were randomly assigned to either placebo (saline) or treatment (BoNT-A) groups. On day 0 of the intervention, 50 units of BoNT-A or an equivalent volume of saline (0.09%) was given into the middle carpal joints. On day 14, acute synovitis was induced with intra-articular injection of recombinant equine interleukin-1 beta (IL-1 beta) 100 ng. Synovial fluid, clinical evaluation of lameness, and kinematic gait analysis were evaluated on day 15.

Synovitis was observed on histology and cytology in all horses after IL-1 beta, indicating acute suppurative inflammation. In the BoNT-A group, one horse developed lameness, whereas the other demonstrated no change in baseline gait evaluation. No adverse effects were observed in joints injected with BoNT-A or with saline alone.

Our findings support the idea that BoNT-A can attenuate lameness in an equine model of acute synovitis. Our findings further suggest that BoNT-A might be a potential new treatment for painful arthritis; this warrants further study.