Ocular myasthenia gravis-like symptoms associated with erenumab: Case report

We present a case of a patient who developed myasthenia gravis (MG)-like symptoms during erenumab treatment.

The patient had a years-long history of chronic migraine with visual and sensory aura. Two months after the beginning of erenumab therapy, she reported intermittent bilateral weakness of the eyelids, with ptosis. The eyelid ptosis was severe enough to block the patient's vision. The symptoms would usually last between 5 and 10 minutes and resolve completely spontaneously, but they repeated on a daily basis. Antibodies against acetylcholine receptors and muscle-specific kinase were all negative, and other work-up excluded the usual etiology of ptosis. Since the cause of symptoms was not detected, we suspected they were induced by erenumab. The treatment was discontinued, and after 7 weeks from the last dose of erenumab, ocular symptoms resolved completely. In the presented case, other possible causes of MG-like symptoms were excluded by diagnostic tests and clinical course of the disease. The temporal relationship between the administration of erenumab and occurrence of ptosis, with regression of the symptoms after the drug discontinuation supports the hypothesis of causal relationship with erenumab. According to the Naranjo's Adverse Drug Reaction Probability Scale, erenumab-related MG-like symptoms were rated 'probable'. Reviewing the literature, we identified no similar case reports.

Drug-induced MG-like symptoms might be life threatening. Therefore, clinicians should be aware of these adverse reactions during the use of erenumab.