NEUROOPHTHALMOLOGICAL EVALUATION OF SUPERIOR OBLIQUE MYOKYMIA

Three cases of superior oblique myokymia (SOM) were analyzed neuro-ophthalmologically using single neuromuscular unit (NMU)-electromyography (EMG), single fiber EMG, and a two-dimensional eye movement analyzing system. The action potentials of the superior oblique muscle had high amplitude, long duration and many turns, and single NMU-EMG of the inferior oblique muscle showed no decrease of discharge synchronized with the burst discharges of the superior oblique muscle. Moreover, the jitter value calculated from single fiber EMG of the superior oblique muscle was relatively small and essentially the same as in normal controls and muscles completely recovered from oculomotor nerve palsy. Two-dimensional eye movement analysis showed unilateral rotary eye movements with a lower frequency than had been previously reported. These studies suggested that the lesion responsible for SOM was in either the ipsilateral trochlear nucleus or its infranuclear tract and that SOM might be associated with the recovery stage of trochlear nerve palsy.