Immune checkpoint inhibitors (ICI) are associated with a variety of immune-related adverse events (irAEs). IrAEs are under diagnosed as they present with a spectrum of non-specific, and often initially subtle, symptoms. These symptoms typically develop shortly after initiation of ICI. Patients may present with symptoms suggestive of disorders such as myasthenia gravis, encephalitis/meningitis, inflammatory polyradiculopathies, or peripheral neuropathy. In this report, we present the case of a patient, with newly diagnosed malignant melanoma, who began to experience a variety of symptoms including bilateral lower extremity weakness weeks after initiating neoadjuvant Ipilimumab & Nivolumab (Ipi/Nivo). 

Patient is a 77-year-old male with a medical history significant for metastatic melanoma diagnosed in 2023 presenting to Neurology clinic in April 2024 for worsening ambulatory dysfunction. Patient reported worsening lower extremity weakness since December of 2023 shortly after he was started on neoadjuvant Ipilimumab & Nivolumab (Ipi/Nivo). By April 2024, his asymmetric bilateral lower extremity weakness and sensory deficits had progressed significantly and he required a walker to ambulate. Workup included MRI of the thoracic spine, which revealed pachymeningitis, EMG findings concerning for left lumbosacral plexopathy, and a nonrevealing lumbar puncture.  

Immune checkpoint inhibitors are associated with a variety of irAEs affecting multiple organ systems. While neurologic symptoms are uncommon, when present they can include symptoms suspicious for myasthenia gravis, GBS, or other various neuropathies. As these medications become more commonly prescribed, neurologists ought to be aware of the relationship between ICI and irAEs. Further characterization and awareness of ICI-associated syndromes are necessary for neurologists to be able to identify and treat patients for irAEs as these medications become more widely utilized.