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Paraneoplastic neurological syndromes (PNS) are defined as remote effects on the central and peripheral nervous system that are not caused directly by the tumor, its metastases and treatment, or metabolic disorders. The most probable cause is a falsely initiated immune reaction. Well-defined classical PNSs are associated with distinct tumors and occur with onconeural antibodies directed against intracellular neuronal antigens. However, response to therapy is limited. Recently, new antibodies directed against neuronal surface antigens were described in encephalitic syndromes of autoimmune origin. These probably antibody-mediated disorders are more frequent than classical PNS, occur with or without tumor association and often show a good response to immunosuppressive treatment. [ABSTRACT FROM AUTHOR]

Antibody-associated limbic encephalitis was usually seen as a paraneoplastic syndrome where the antibodies would target intracellular proteins. However, recent reports challenged this idea and described antibodies that target synaptic proteins expressed on the cell surface. These antibodies are not necessarily linked to tumors and should be regarded as a distinct entity of different autoimmune diseases. They are of direct clinical relevance since their binding to their target antigen is likely the cause of the clinical symptoms and, therefore, immune treatment often results in a beneficial outcome. Tests which differentiate these antibodies are now available in specialized laboratories. [ABSTRACT FROM AUTHOR]