Mononeuritis multiplex as a rare and severe neurological complication of immune checkpoint inhibitors: a case report

Background Mononeuritis multiplex is a rare autoimmune peripheral neuropathy that typically presents in the context of vasculitis, diabetes, infection, or as a paraneoplastic syndrome. Adverse immune-related neurological conditions have been increasingly reported with the use of immune checkpoint inhibitors against cytotoxic T-lymphocyte antigen-4 and/or the programmed cell death protein 1/programmed death ligand-1 axis. Mononeuritis multiplex has only been reported twice from treatment of cancers with immunotherapy. Case presentation Here we report a case of mononeuritis multiplex as a complication of immune checkpoint inhibitor therapy for melanoma. An 80-year-old non-Hispanic white female with recurrent melanoma was treated with combination ipilimumab and nivolumab and subsequently presented with progressive leg weakness, back pain, and difficulty ambulating. The diagnosis of mononeuritis multiplex was made, which was resistant to steroid pulses, chronic steroids, intravenous immunoglobulin, and rituximab. She developed progressive neurologic dysfunction and elected for hospice care. We found only two other cases reported in the literature. Conclusions Increased awareness, prompt recognition, and aggressive treatments are likely the best opportunity for improved outcomes in this severe side effect.