Pembrolizumab-induced myasthenia gravis: A fatal case report

Purpose Pembrolizumab, a monoclonal antibody which inhibits the programmed cell death 1 receptor, has been shown to efficaciously enhance pre-existing immune responses to malignancies. However, safety concerns must also be considered as pembrolizumab use has been associated with several life-threatening immune-related adverse events (irAEs). We report a fatal case of pembrolizumab-induced myasthenia gravis in a patient with no prior myasthenia gravis history. Case report A 63-year-old male presented with right eyelid drooping, puffiness, blurred vision, and shortness of breath two weeks after an initial infusion of pembrolizumab. He was subsequently diagnosed with new onset acetylcholine-receptor positive myasthenia gravis. Despite aggressive treatment with corticosteroids, pyridostigmine, intravenous immunoglobulin, and plasmapheresis, the patient clinically deteriorated and ultimately expired from acute respiratory failure after a 12-day hospitalization. Discussion Current package labeling for pembrolizumab warns against various irAEs associated with its use including pneumonitis, colitis, and endocrinopathies. To date, only one case of new onset myasthenia gravis and two case reports of myasthenia gravis exacerbation have been identified. This case further highlights the mortality risk associated with development of irAEs. Conclusion While rare, evidence for the development of MG associated with pembrolizumab is growing. Prompt recognition of symptoms and discontinuation of pembrolizumab is necessary to help improve prognosis.