The use of electromyographic examination as a diagnostic tool and phenytoin sodium as treatment in a case of classic springhalt in a Dutch warmblood horse

: This paper describes a case of unilateral stringhalt present for 18 months in the right hind limb of a 4-year-old Warmblood gelding. The only abnormalities detected by electromyography (EMG) were a prolonged insertion activity, fibrillation potentials, and positive waves at rest and enhanced EMG activity in the right lateral digital extensor muscle on muscle contraction. This was interpreted as denervation and hyperirritability of this muscle. Both similarities and differences with Australian stringhalt could be found. As described for horses suffering from Australian stringhalt, phenytoin sodium was administered orally in a dosage ranging from 15 to 9.3 mg/kg body weight in order to try to influence the hyperflexia. Therapeutic effects without side effects could be achieved at plasma concentrations between 5.1 and 9.9 mg/L at a dosage of 12 mg/kg body weight twice daily, which is consistent with data in the literature (5-10 mg/L). The EMG examination seems to help to clarify the aetiology of the classical form of stringhalt, since the only abnormality in this patient was an abnormal electrical activity in the lateral digital extensor muscle. As in Australian stringhalt, in this type of stringhalt phenytoin also relieved the hyperflexion of the tarsus.