An Outbreak of Stringhalt Resembling Australian Stringhalt in Japan

We report four cases resembling Australian stringhalt observed for the first time in Japan. Between June and July 2000, three of four 4-year-old thoroughbred mares that had been grazed on the same pasture suddenly suffered exaggerated flexion of both hindlimbs. Subsequently, the remaining horse also exhibited mild stringhalt in October. The last horse recovered without treatment one month after occurrence, but the other three horses exhibited severe stringhalt even 5-6 months after occurrence. In one horse, endoscopic examination revealed a left laryngeal hemiplegia. Three of four cases were treated with a combination of drug based treatment (baclofen and phenytoin) and exercise. While phenytoin was effective in treating the stringhalt, the baclofen had no effect. Once the stringhalt improved, treadmill exercise was started to improve hindlimb function. As a result, two of the three horses were able to canter. Three cases underwent electromyography examination and motion analysis. Before treatment, high amplitude electric discharges were observed in the long digital extensor muscle and the lateral digital extensor muscle in the swing and stance phase. The angle of each joint flexed extensively in the swing phase. While Australian stringhalt may heal spontaneously over time, therapy with phenytoin and exercise may hasten a cure.