Autoimmune Encephalitis Related to Cancer Treatment with Immune Checkpoint Inhibitors: Systematic Review

ABSTRACT BACKGROUND Immune checkpoint inhibitors (ICPI) are a game changer in the treatment of various metastasized cancers, but emerging reports of adverse events, including ICPI-associated autoimmune encephalitis (ICPI-AIE), are concerning. We aimed to collect all published cases of ICPI-AIE to identify the salient clinical and laboratory features of this disorder. METHODS We searched PubMed, The Cochrane Library and Embase for ICPI-AIE cases from the first description in 2015 until 01/2020 using standard bibliographic measures including PRISMA guidelines and pre-registration with PROSPERO (CRD42019139838). RESULTS Thirty-nine studies met inclusion criteria, resulting in 54 ICPI-AIE patients (mean age 58.6 years; 43% females). Common cancers included melanoma (30%) and non-small cell lung cancer (30%). Brain metastases were found in 16 patients (30%). The most frequent ICPI was nivolumab (61%). Onset of ICPI-AIE occurred on average after 3.5 treatment cycles, but very early and late presentations were common. Non-limbic AIE was roughly twice as frequent as limbic AIE (p<0.05). The most common laboratory abnormalities included bitemporal FLAIR lesions on MRI, continuous slow waves and diffuse slowing on EEG, and monocytic pleocytosis on cerebrospinal fluid analysis. Of note, intraneuronal antibodies were more frequent than neuronal surface antibodies, and logistic regression identified the presence of intracellular antibodies as a significant predictor for lack of improvement after 1 st line immunotherapy (p<0.05). CONCLUSIONS ICPI-AIE consists of a heterogenous group of conditions. Neurologists will likely encounter ICPI-AIE more often in the future, but important unresolved questions include the exact pathophysiological mechanisms, the epidemiology and the best treatment approaches associated with ICPI-AIE.