Stimulated Single-Fiber EMG In The Ocular Myasthenia Gravis And In Some Ocular Myopathies

Abstract

The aim of this study was to evaluate the role of stimulated single fiber electromyography (ST‐SFEMG) in differentiating ocular myasthenia gravis (OMG) from some myopathies with ocular involvement. We performed ST‐SFEMG in the orbicularis oculi muscle in 65 patients diagnosed with OMG, in 11 chronic progressive external ophthalmoplegia and 3 oculopharyngeal muscular dystrophy. 97% of OMG and 21.4% of myopathic patients had 10% o more motor potentials (MP) exceeding 35 μs. 95% of OMG and 14.3% of myopathic patients had 15% o more MP exceeding 35 μs. 89% of OMG and 7.1% of myopathic patients had 20% o more MP exceeding 35 μs. 72% of OMG and 0% of myopathic patients had 25% o more MP exceeding 35 μs. It is possible to discern between OMG and ocular myopathy by ST‐SFEMG and that the cutoff criteria is 25% MP with jitter over 35μs in orbicularis oculi muscle.