Electromyographic analysis of canine distemper myoclonus

Canine distemper myoclonus was electromyographically analysed to throw more light upon the condition without invasive surgical intervention. Although myoclonus seemed to occur synchronously in many muscles, the onset of myoclonus appeared to be slightly earlier in one or two particular muscles and, furthermore, myoclonus did not arise temporally in descending or ascending order along the neuroaxis. Myoclonus-like discharges were evoked by tendon-tapping and this feature disappeared after cessation of myoclonus. In successive myoclonic bursts, a significant positive correlation was noted between the silent period and the subsequent discharge period, independently of the level of consciousness, i.e., the longer the silent period, the longer the subsequent episode of myoclonus. This correlation was re-established very early after recovery from anesthesia with halothane, when electroencephalograms showed slow waves. These results strongly indicate that the lower motor neurons may be the primary site responsible for the genesis of canine distemper myoclonus.