Novel uses of complement inhibitors in myasthenia gravis—Two case reports

Abstract Introduction/Aims Myasthenia gravis (MG) is a rare, life‐threatening immune‐related adverse effect (irAE) of immune checkpoint inhibitor (ICI) treatment. C5‐complement inhibitors are effective treatments for acetylcholine receptor antibody (AChR ab) positive generalized MG. We describe the use of eculizumab/ravulizumab in two patients with MG receiving concomitant pembrolizumab. Methods This was a retrospective review of two medical records. Results Patient 1: An 80‐year‐old male with recurrent, non‐muscle invasive transitional cell carcinoma of the bladder developed ICI‐induced AChR ab positive MG (ICI‐MG), myositis, and myocarditis 2 weeks after the first dose of pembrolizumab. Myositis responded to corticosteroids. MG responded to eculizumab, followed by ravulizumab. He died of metastatic cancer 8 months later. Patient 2: A 58‐year‐old male had refractory thymoma‐associated AChR ab‐positive MG, which responded to eculizumab. He developed metastatic Merkel cell cancer necessitating pembrolizumab. MG remained stable on eculizumab. He had no irAEs for 22 months, with positron emission tomographic resolution of cancer. He then developed mild, indolent retinal vasculitis, which responded to prednisone. Discontinuation of pembrolizumab for 5 months resulted in cancer recurrence; pembrolizumab was resumed with peri‐infusion pulse prednisone. MG remained stable and he continues eculizumab. Discussion In the first patient, eculizumab, followed by ravulizumab, improved ICI‐MG. In the second patient, eculizumab treatment may have had a prophylactic effect on the development of ICI‐induced irAEs. The effect of complement inhibition on cancer outcomes of ICI therapy is unknown. A possible biologic basis for complement inhibitors in reducing irAEs of ICI, especially in the presence of underlying autoimmune disease, merits evaluation.