Saccade fatigue and response to edrophonium for the diagnosis of myasthenia gravis.

Maximum velocity and amplitude of repetitive ( 1-per-second) 30 degrees saccadic eye movements were quantitatively assessed for 4 minutes before and after intravenous edrophonium chloride as a diagnostic test for myasthenia gravis. Atropine was given initially to suppress muscarinic side effects. Eye movements were recorded by electrooculography and a digital computer identified saccadic eye movements and plotted amplitude-velocity relationships. When compared with control subjects, eleven of twelve patients with proven MG had a significant increase in saccade amplitude and/or maximum velocity after edrophonium chloride. Only three of twelve proven MG patients had clinically apparent extraocular muscle weakness. The initial period of fatigue improved the sensitivity of the test in those patients who began with normal saccade amplitude and maximum velocity. Two of the patients with positive saccade fatigue tests had no change in optokinetic nystagmus amplitude before and after edrophonium chloride. It is concluded that, quantitative assessment of repetitive large angle saccades before and after edrophonium chloride is a sensitive test for extraocular muscle involvement in MG.