Changes in psychophysiological processing of vision in myasthenia gravis.
OBJECTIVE: To investigate the possibility of impaired central nervous system (CNS) cholinergic transmission in myasthenia gravis (MG), and the effect of eye movements and particularly of micromovements in the psychophysiology of vision. MATERIALS AND METHODS: Fourteen patients with clinical manifestations of external ophthalmoplegia due to different causes (nine patients with myasthenia gravis and five with ocular myopathy) were examined. Simultaneous recording of eye movements (optical method) and pattern reversal-visual evoked potentials (PR-VEPs) were performed. RESULTS: Eye micromovements during fixation were impaired in both groups. A statistically significant difference (P < 0.01) was found in the amplitude of P100 of PR-VEPs before and after treatment in MG patients, and also between normal controls and MG patients before (P < 0.001) and after treatment (P < 0.01). P100 latency of the PR-VEPs in MG patients before and after treatment was delayed compared to normal controls, while there were no differences between ocular myopathy patients and normal controls. CONCLUSION: The eye movement impairment observed in MG patients is not sufficient to explain abnormal PR-VEPs detected in these patients. These results provide neurophysiological evidence of impaired cholinergic transmission in the central nervous system in patients with MG and suggest that PR-VEPs offer an easily applicable non-invasive method to study the central effects of MG.