Single-fiber electromyography in the orbicularis oculi muscle in patients with ocular myasthenia gravis symptoms: does abnormal jitter predict response to treatment?

BACKGROUND Seronegative ocular myasthenia gravis (OMG) is diagnosed by ocular symptoms with supporting SFEMG, typically of frontalis or extensor digitorum muscles. We aimed to determine the sensitivity and specificity of orbicularis oculi SFEMG to diagnose and exclude myasthenia gravis and predict response to therapy. METHODS Orbicularis oculi SFEMG studies were conducted in 142 consecutive patients with symptoms and/or findings of OMG and negative AChR antibody during the period of 5 years. Retrospective chart review was conducted 2 years after the SFEMG to determine whether treatments were given and responses to treatment. RESULTS Orbicularis oculi SFEMG was abnormal in 31 patients and normal in 111 patients. Twenty-nine patients with abnormal SFEMG were treated, and 25 had a good response. Twenty-four patients with normal SFEMG received treatment; none responded to treatment or developed generalized myasthenia. CONCLUSION An abnormal orbicularis oculi SFEMG in patients with seronegative OMG has a high predictive value for response to therapy. Our study findings may affect the treatment decisions in practice and aid better management of myasthenic patients.