NCMP-24. Bulbar Myasthenic Syndrome in a 65 year-old Woman with Melanoma during treatment with Pembrolizumab: Case Report

A 65 year old woman with a past medical history of melanoma treated with resection and Pembrolizumab (three doses, last dose 1/2025) presented in February 2025 with decreased oral intake, dysphagia, dysphonia, ptosis, and diplopia. Upon admission, she had bilateral upper extremity weakness. Exam was notable for severe bilateral ptosis, ophthalmoplegia in all directions, right eye exotropia, 4/5 strength in neck flexion and extension, negative Bienfang’s and curtain signs, and no fatiguability. NIFs worsened from -60 to -30 without other signs of respiratory distress. AchR, LEMS, MUSK, VGCC antibodies were negative. Creatine kinase was mildly elevated at 274. MRI Brain/Orbits showed hypertrophy and enhancement of the of the bellies of the extraocular muscles bilaterally concerning for myositis. EMG did not show abnormalities although bulbar muscles were not tested. There wasn’t any symptomatic improvement with pyridostigmine. Patient underwent five doses of IV Solumedrol, followed by five doses of PLEX and five doses of IVIG. Patient’s respiratory status improved throughout hospitalization. With mild improvement in remaining symptoms, patient was discharged on oral prednisone and cyclosporine. Her neuromuscular status improved after discharge; Pembrolizumab remains on hold. Immune checkpoint inhibitors are a class of immunotherapy that prevents interaction between tumor cells and the immune system to encourage immune response and tumor cell destruction. Immune-related adverse events (IrAE) occur when T cell activation exceeds desired function and induces unwanted inflammatory responses in other organs. While neurological adverse events are rare, there have been documented IrAEs targeting the central and peripheral nervous systems (CNS, PNS). Myopathies and myasthenic syndromes are the most common neurological complications in the PNS, after polyradiculopathies and neuropathies. Early identification and treatment are essential for functional recovery and future oncological management.1 1. Roth P, Winklhofer S, Muller AMS, et al. Neurological complications of cancer immunotherapy. Cancer Treat Rev. 2021;97:102189. doi:10.1016/j.ctrv.2021.102189