Abstract
With the success of immuno-oncotherapy (IO) to treat systemic cancers came the risk for multi-organ autoimmune inflammation (esophagitis, colitis, hypophysitis, pneumonitis, etc.). Immune-mediated encephalitis, however, has been only rarely described in patients treated on IO. Here we present the first case of a 70-year-old male with history of clear cell renal cell carcinoma (CCRCC, Fuhrman grade 4, April 2017) post-nephrectomy with early progressive pulmonary metastases treated with pazopanib before switching to single-agent nivolumab (February 2018) with demonstrated early response. Further progression (March 2019) added body irradiation and continued systemic nivolumab with questionable medication-induced dermatitis. Patient presented to ED in May 2019 with new-onset generalized tonic-clonic seizure, left visual field cut, and 4.6cm heterogeneous enhancing right occipital mass with vasogenic edema on brain MRI, presumed metastasis. However, unknown to the patient was a remote area of right occipital encephalomalacia (found on skull-based portion of staging PET, July 2018) presumed silent stroke or TBI endorsed 20-years-ago. Patient started anti-epileptic therapy and underwent negative CSF evaluation before neurosurgical resection. Tissue pathology concerning for lymphoproliferative malignancy versus reactive lymphocytic infiltrate with perivascular distribution of monomorphic CD4+ T-cell predominance (97%) and positive T-cell receptor (gamma, beta) gene rearrangement. While clonal T-cell populations are highly suggestive of T-cell malignancies, reactive conditions can also rarely show clonal T-cell populations. Patient underwent a negative systemic staging for lymphoma and IO was discontinued without immediate initiation of steroids. Follow up clinical evaluation reveal patient improved off IO therapy. Patient was determined to have reactive immune-mediated encephalitis secondary to IO therapy causing seizure mimicking brain metastasis of primary CCRCC. Interestingly, the prior area of encephalomalacia allowed for a cellular bed to collect, resembling brain mass. Upfront staging brain MRI prior to starting IO might have revealed susceptible area and could be considered in these patients