Pembrolizumab-Induced Myasthenia Gravis With Myocarditis in the Setting of Metastatic Renal Cell Carcinoma

Immune checkpoint inhibitors (ICIs) like pembrolizumab are increasingly used for treating renal cell carcinoma (RCC), offering benefits such as enhanced specificity and activation of immunological memory. However, ICIs can lead to immune-related adverse events (irAEs), including rare but serious neurologic consequences such as myasthenia gravis (MG). We present a case of pembrolizumab-induced MG with concurrent orbital myositis and myocarditis. A 69-year-old male with a history of pT3aN1 kidney cancer presented with abdominal pain, night sweats, and weight loss. Initial imaging revealed a retroperitoneal mass and a thyroid mass, and a biopsy confirmed papillary RCC. The patient began neoadjuvant therapy with pembrolizumab and axitinib. Three weeks post-initiation, he developed dysphagia, ptosis, and proptosis, which progressed with each pembrolizumab infusion. Hospitalization was required after the third cycle due to bilateral ptosis, heart block, and elevated troponins. Despite initial steroid treatment, symptoms persisted. Diagnoses of ICI-related MG (irMG) and myocarditis were established, and treatment included cessation of pembrolizumab, high-dose steroids, IVIGs, and a pacemaker for heart block. Post-discharge, the patient showed a slight improvement in ptosis but persistent dysphagia. MG induced by ICIs is a rare but severe complication with rapid onset and progression, often presenting with bulbar involvement and a significant risk of respiratory failure. The therapeutic regimen for our patient, including high-dose methylprednisolone and IVIG, aligns with current recommendations. This case underscores the importance of recognizing cardiac irAEs like myocarditis in patients on ICIs, as early intervention can significantly affect outcomes. Despite therapeutic interventions, complete resolution of irMG symptoms is rare, and persistent sequelae are common. This case highlights the critical need for vigilant monitoring and prompt management of neurologic and cardiac irAEs in patients undergoing ICI therapy. Clinicians should maintain a high index of suspicion for MG and myocarditis to improve diagnostic accuracy and patient outcomes.