Paraneoplastic syndrome is an abnormal immune response caused by the products of a tumor. It can cause lesions in endocrine, neurological, digestive, hematopoietic, bone and joint, renal and skin systems. If it occurs in the nervous system, it is called neurological paraneoplastic syndrome. Paraneoplastic neurological syndrome affects any part of the nervous system and can involve the central nervous system, producing diffuse gray matter encephalopathy, cerebellar degeneration, cancerous myelopathy, and limbic encephalitis. It can also involve the peripheral nervous system, producing polyneuropathy, neuritis, etc. Accumulation of neuromuscular junction can produce myasthenia gravis, Lambert-Eaton muscle weakness syndrome, neurogenic myalgias, and dermatomyositis or polymyositis.