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To better define electrophysiological abnormalities in myasthenia gravis (MG) patients with muscle-specific tyrosine kinase (MuSK) antibodies (Ab), we compared electrophysiological features of 14 MuSK Ab-positive, 73 acetylcholine receptor antibody (AChR Ab)-positive, and 22 MuSK and AChR Ab-negative (seronegative) patients with generalized disease. Repetitive nerve stimulation (RNS) abnormalities were observed in 86% of MuSK Ab-positive and 82% of AChR Ab-positive patients but in only 55% of seronegative patients. RNS decrements in the orbicularis oculi were more common and severe in the MuSK Ab-positive patients than the other two groups. Single-fiber electromyography (SFEMG) of the extensor digitorum communis was abnormal in 90% of MuSK Ab-positive patients. The high frequency of RNS abnormalities in facial muscles in the MuSK Ab-positive population reflects the propensity for facial muscle involvement in this form of MG and emphasizes the importance of including facial muscles in RNS protocols when evaluating these patients.

Background: Relative afferent pupillary defects are typically related to ipsilateral lesions within the anterior visual pathways., Objective: To describe a patient who had a workup for headache and was found to have an isolated left relative afferent pupillary defect without any other neurological findings., Design: We review the neuroanatomy of the pupillary light reflex pathway and emphasize the nasotemporal bias of decussating fiber projections, which accounts for the relative afferent pupillary defect contralateral to the described lesion. Result Magnetic resonance imaging of the brain revealed a pineal tumor compressing the right rostral midbrain., Conclusion: While rare, a relative afferent pupillary defect can occasionally occur secondary to lesions in the postchiasmal pathways. In these circumstances, the pupillary defect will be observed to be contralateral to the side of the lesion.