A 73 years-old man referred for subacute left lower-limb hyposthenia and urinary incontinence over two weeks, reporting a history of clear cell renal carcinoma with left nefrectomy two years earlier, followed by first-line chemiotherapy and ongoing second-line treatment with nivolumab for two pulmonary localizations. Spinal cord MRI revealed an intensive contrast-enhancing intramedullary lesion at T8-T9 surrounded by wide intramedullary T2-hyperintensity, extended from T3 to conus and suggestive for an inflammatory process. Cerebrospinal fluid analysis showed hyperproteinorrachia (80 mg/dl) with three lymphocytes and no malignant cells. Microbiological examination (neurotropic viruses, HIV, Borrelia) ruled out an infective etiology and isoelectrofocusing revealed a mirror pattern. Immunological screening and paraneoplastic antibodies were unremarkable, serum aquaporin-4 immunoglobulin G and anti-myelin oligodendrocyte glycoprotein antibodies were negative as well. Visual evoked potentials were delayed bilaterally. Brain MRI showed an enhancing lesion at cerebellum suspected for secondary localization of renal neoplasia, without evidence of focal white matter inflammatory alterations. 

Patient was diagnosed with myelitis suggestive for neuromyelitis optica spectrum disorder secondary to nivolumab administration and put on high-dose steroid treatment with mild clinical and radiological improvement. He was then referred to surgical removal of cerebellar lesion.