A 69-year-old female with squamous cell carcinoma of the skin presented with acute-onset diplopia. She had completed two cycles of cemiplimab with the last dose administered two weeks prior to symptoms of diplopia. During the neurological examination, she exhibited gaze limitation in all directions. Laboratory results showed elevated CK (3485 U/L) and elevated troponin (450 ng). Myasthenia gravis-related antibodies were negative. MRI scans of the brain and orbit, cerebrospinal fluid analysis, electromyography, echocardiogram, and cardiac MRI were unrevealing. In spite of receiving 5 days of intravenous immunoglobulin (IVIG) and thymoma resection, the patient continued to deteriorate over the next ten days, resulting in upper and lower extremity weakness, dysphagia, and dyspnea that eventually required intubation. She underwent plasma exchange followed by a second round of IVIG and was started on prednisone with minimal improvement.
Rituximab was initiated at a dose of 500mg/m2 every two weeks for two doses. Over the following three months, the patient exhibited significant improvement, ultimately discontinuing ventilation and tube feeds. She was discharged home with the ability to perform activities of daily living independently.