Successful Treatment of Immune Checkpoint Inhibitor-Induced Myocarditis, Myositis, and Myasthenia Overlap Syndrome With Baricitinib and Abatacept.

Immune checkpoint inhibitor (ICI) therapies are known to cause immune-related adverse events (irAEs), including life-threatening myocarditis, myositis, and myasthenia (MMM) overlap syndrome. Current literature lacks established therapeutic guidelines for effective management with steroid-sparing agents. In this paper, we report the successful treatment of MMM with baricitinib in conjunction with abatacept (CTLA-4-Ig) in a single patient. We report two cases with a history of locally advanced malignancies treated surgically who were receiving adjuvant ICI therapy and subsequently developed MMM overlap syndrome. Case A was treated with high-dose corticosteroids, IVIG, and mycophenolate mofetil with no improvement and subsequently expired due to respiratory failure and cardiac arrest. On the other hand, Case B showed improvement of myocarditis and myositis with high-dose corticosteroids, abatacept, and mycophenolate mofetil. However, myasthenic symptoms progressed. Discontinuation of mycophenolate mofetil and initiation of baricitinib resulted in a complete recovery at 2-month follow-up. The use of baricitinib in combination with abatacept resulted in significant improvement of ICI-induced MMM in our patient. We propose that in patients with ICI-induced MMM, baricitinib with abatacept can be used effectively with successful outcomes, especially for refractory myasthenic symptoms. Further clinical trials on the use of JAK inhibitors alone or in combination with abatacept will be beneficial in determining its efficacy.