Clinical characteristics and outcome of patients with autoimmune encephalitis: clues for paraneoplastic etiology

BACKGROUND: Autoimmune encephalitis (AE) represents a complex syndrome with diverse clinical manifestations and therapeutic outcomes. Aim of this study is to report the clinical characteristics and the long-term outcome of patients with paraneoplastic and idiopathic AE. METHODS: All patients with subacute encephalopathy admitted to the Neurology Department of our Institution from January 2012 to May 2019 were consecutively enrolled. Patients' serum and cerebrospinal fluid (CSF) were tested for neural-specific autoantibodies (Ab) by indirect immunofluorescence assays on mouse brain, rat neurons, cell-based assays and immunoblots. Outcome was assessed by the modified Rankin Scale score (mRSs). RESULTS: From 107 adult patients with subacute encephalopathy, 50 patients were finally diagnosed with AE. Neural Ab were detected in 45/50 patients (90%). Lgi1-IgG was the most frequent (6/50, 12%) Ab specific to neural surface antigens (NsAb) detected in adults with AE. Paraneoplastic encephalitis was diagnosed in 16/50 patients (32%). The presence of bilateral temporal lobe lesions at MRI and CSF-restricted oligoclonal bands (OCB) was associated with higher probability to detect cancer at the time of AE diagnosis. All patients with NsAb had a good outcome at last follow-up. Severe disability at AE onset and the lack of long-term immunosuppression predicted a poor outcome. CONCLUSIONS: Lgi1-IgG was the most frequent Ab detected. Patients with bilateral temporal lobe lesions and OCB have higher probability to harbor an occult tumor. In these patients a strict surveillance and monitoring for cancer detection is recommended.