To describe the clinical features and antibody repertoire of thymoma-associated autoimmune encephalitis.

Thymomas are one of the most frequent tumors associated with autoimmune encephalitis; the frequency of neural surface antibodies (NS-ab) is unknown.

NS-ab were detected in 31/50 (62%) patients. Compared with the 19 NS-ab negative patients, those with NS-ab were more likely to have limbic encephalitis (20% vs 5%), Morvan syndrome (14% vs 5%), seizures (55% vs 25%), multifocal cortico-subcortical FLAIR MRI abnormalities (43% vs 25%) and clinical relapses (27% vs 5%) [p<0,05]. Other clinical features were not significantly different: neuromyotonia (7% vs 10%), stiff-person syndrome/PERM (9% vs 5%), or myasthenia (36% vs 42%). GABAaR antibodies were the most prevalent (in 12 cases). Other NS-ab included: 4 LGI-1; 2 AMPAR; 1 CASPR2; 1 NMDAR; 2 GlyR (1 with concurrent GAD); 1 AQP4; 2 LGI1 + CASPR2; 1 GABAaR + LGI1; 1 GABAaR + AMPAR; and 1 CASPR2 + AMPAR + GABAbR; in the remaining 3 patients the identity of the antigens was unknown. Antibodies against onconeuronal antigens (2 CRMP5, 1 Hu, 1 Ma2) were only identified in the group of patients with NS-ab. Age, sex, tumor characteristics, inflammatory CSF, EEG findings, treatments, and outcome were similar in NS-ab positive and negative patients (not shown).