Late-Onset Ocular Myasthenia Gravis–Like Symptoms During Erenumab Therapy for Chronic Migraine: A Case Report

Chronic migraine (CM) is a disabling neurological disorder for which calcitonin gene-related peptide (CGRP)–targeted monoclonal antibodies, such as erenumab, provide effective prophylaxis. Although generally well tolerated, rare neuromuscular complications resembling ocular myasthenia gravis (MG) have been reported. A 46-year-old woman with CM achieved marked improvement with erenumab for over three years before developing diplopia and intermittent ptosis. Laboratory and imaging studies were unremarkable, but clinical suspicion for MG led to pyridostigmine therapy, resulting in rapid improvement. Brief episodes of dysarthria occurred but resolved within one month. Symptoms disappeared after discontinuation of erenumab and continued pyridostigmine. On re-initiation of erenumab, the patient maintained migraine control without recurrence of MG-like symptoms. This case illustrates a rare, late-onset, reversible MG-like complication of erenumab. Clinicians should remain alert to ocular manifestations even as delayed adverse effects of anti-CGRP therapy.