Paraneoplastic and Nonparaneoplastic Autoimmune Syndromes of the Nervous System
Autoimmune syndromes of the nervous system can be divided into those which are consistently associated with tumors and those which are not. The former, often termed paraneoplastic, are defined as disorders caused by a systemic cancer that are not a direct result of tumor invasion and are believed to be a result of an immune response to antigens shared by the cancer and the nervous system. Many paraneoplastic disorders typically associate with serum autoantibodies which can help establish the diagnosis of a paraneoplastic syndrome and often suggest the primary site of the cancer. However, these antibodies are typically noncausative as they usually target intracellular antigens. By contrast, the latter group of nonparaneoplastic conditions often associate with autoantibodies which can access their neuroglial surface target antigen in vivo, and hence are directly autoantibody-mediated. Both sets of conditions can involve any portion of the nervous system, either a single area or cell type (e.g., Purkinje cells of the cerebellum) or more extensively (e.g., encephalomyelitis). Treatment paradigms usually require both cancer therapy and immunosuppression. Outcomes are often best in the patients without tumors, some making almost complete recoveries.