New Treatment for Headshaking in Horses

However, a new procedure has been developed and is still being monitored. Clinical trials of percutaneous electrical nerve stimulation (PENS neuromodulation) were pioneered at the University of Bristol in August 2013 and results were published in 2014.

The procedure involved the use of a probe that was inserted just beneath the skin and next to the nerve in question. Seven horses diagnosed with trigeminal-mediated headshaking were selected for the trials. They were sedated and the skin was desensitized with a local anesthetic during the probe’s insertion under ultrasonographic guidance. The nerve was then stimulated for 25 minutes following a protocol of alternating frequencies based on human clinical data. The probe was removed and the procedure repeated on the other side. Three treatments were done during the trials, each one repeated when signs of headshaking returned.

“All the horses tolerated the procedure extremely well under standing sedation, although there remains a risk to performing any procedure in a conscious horse,” says Roberts. “Side effects have been minimal with a few horses having a hematoma at the site of probe insertion, which resolved uneventfully without treatment and did not appear to cause any problems. Five horses returned to ridden work following their third procedure, with an average remission time of 15.5 weeks. One horse responded to the first procedure but not to later ones.”

The protocol guideline is that the second procedure is done five days after the first and the third procedure is done about ten days after the second. After that, two to three weeks is allowed to gauge the horse’s response.

“It certainly seems to be the case that horses can respond to the third treatment when they did not [respond] to earlier ones, so we should try three procedures before deciding if the horse will respond to treatment,” she says. “Some horses have a promising start but then fail to respond to later treatments. Some horses don’t respond at all, and some only for a short time. It is my early impression that where horses respond, but for insufficient time, length of remission may increase with repeated procedures. It is still very early days and we have a lot to learn and refine.”

Roberts says that trigeminal-mediated headshaking still carries a poor prognosis, even with the availability of neuromodulation. “I do think the future in treatment lies in regulating the nerve’s function back to normal and neuromodulation may be the way to do that for many individuals. We are still just using a human protocol stuck on to a horse so it needs refinement and development.”

All the horse owners were advised to lunge their horses each day to assess their behaviour following each treatment. If they appeared comfortable and were not headshaking, they could proceed to riding while watching for reactions.