New concepts in paraneoplastic neurological syndromes.

Paraneoplastic neurological syndromes (PNS) are rare diseases defined so far by the presence of a neurological disorder associated with cancer in the absence of invasion of the nervous system by tumor cells. Discovery of circulating autoantibodies specific for these patients has revolutionized the diagnosis and understanding of these syndromes and demonstrated a role of the immune system in the neurological syndromes. Until recent years, we thought that these autoantibodies were only markers of the disease and had no role in the pathophysiology. The recent description of autoantibodies directed against membrane receptors or channels and playing a direct pathological role has transformed the concept of PNS. Especially, it appears that many patients may have a neurological syndrome and autoantibodies without cancer. This results in a classification based on the nature of the autoantibodies associated with neurological syndrome. In case of autoantibodies targeting intracellular antigens, cancer is almost always associated, the neurological disorders are mainly related to neuronal death, patients are rarely sensitive to immunomodulatory treatments and cellular immunity appears to play a major role. In contrast, patients with autoantibodies targeting membrane antigens (receptors, channels or receptor associated proteins) have rarely cancer, neurological disorders are related to a reversible neuronal dysfunction, patients are mostly sensitive to immunomodulatory treatments and it seems that humoral immunity and autoantibodies play a major role.