AQP4 and syphilis: 28% of patients belonged to the systemic autoimmune diseases (NPLE and Hashimoto’s encephalopathy), coexisting neuronal antibodies, antibody-negative autoimmune encephalitis, infection-related neuronal antibody positive group (syphilis and Listeria monocytogenes infections) and atypical AQP4-IgG, which presented with encephalitis syndrome (Fig. 1).