Update on paraneoplastic neurologic disorders.

Once considered rare, paraneoplastic neurologic disorders (PNDs) are an extensive group of neurologic disorders that occur either exclusively or at increased frequency in patients with cancer. PNDs have been increasingly recognized due in large part to the identification of antineuronal antibodies in the serum and cerebrospinal fluid of patients. Although almost any neoplasm can cause PND, the tumors most commonly involved are small-cell lung cancer, cancers of the breast and ovary, thymoma, neuroblastoma, plasma cell tumors, and ovarian teratoma. Establishing the diagnosis of PND is important because in more than two-thirds of patients the neurologic symptoms develop before the presence of the cancer is known. When PND is suspected and no tumor is found, it is recommended that cancer screening be repeated every 6 months. Early diagnosis and intervention offers the best chance of neurologic stabilization or improvement.