Single fiber electromyography of extraocular muscles: a sensitive method for the diagnosis of ocular myasthenia gravis.

We performed single fiber electromyography (SFEMG) in the superior rectus and levator palpebralis (SR-LP) muscles of 17 patients with pure ocular myasthenia gravis (MG) and 9 controls. Thirteen patients were also assessed with SFEMG in the orbicularis oculi (OO) muscle. All the MG patients but none of the control subjects showed abnormal SFEMG jitter in the SR-LP muscles. On the other hand, only 62% of the MG patients had abnormal SFEMG jitter in the OO muscle. The procedure was well tolerated by the patients, and complications were minor. We conclude that SFEMG of the SR-LP muscles is a safe and highly sensitive technique for the diagnosis of ocular MG.