Paraneoplastic syndromes are neurological disorders that arise as the "remote effect" of a cancer that does not directly involve the nervous system. The underlying cause of such syndromes is not certain, but it is theorized that these syndromes arise as a result of the body launching an immunological attack against the cells of the nervous system. It is thought that the presence of systemic cancer causes antibodies to be made against the tumor cells. Some of these antibodies, however, become directed against nerve cells, thus giving rise to the host of diseases which constitute the paraneoplastic syndromes. Paraneoplastic syndromes are very rare.
What are the different types of paraneoplastic syndromes?
The types of syndromes resulting from the remote effects of cancer are varied and only the major ones are discussed here:
Cerebellar degeneration can lead to gait ataxia (an inability to smoothly coordinate muscle movements during walking), nystagmus, and dysarthria, a disturbance of speech. Cerebellar degeneration is usually secondary to cancers of the breast, ovary, and female genital tract.
Sensory neuropathy refers to the degeneration of nerve cells specialized for the appreciation of sensations from the body surface. Therefore, people with this paraneoplastic syndrome typically experience: numbness, abnormal burning or tingling sensations in the distal extremities (paresthesia), severe pain, and an impairment of one's position sense (sensory ataxia). This syndrome usually arises secondary to lymphoma.
Lambert-Eaton syndrome (LES) is a neuromuscular disease characterized by the presence of antibodies directed against the terminals of nerves innervating voluntary muscle. Clinically the disease is characterized by limb weakness (especially of the legs), muscle stiffness, drooping eyelids (ptosis), and double vision (diplopia).
Encephalomyelitis is a term used to describe inflammation of any part of the brain or spinal cord. Different forms of encephalomyelitis can arise as the result of a remote tumor. Limbic encephalomyelitis refers to the inflammation of that part of the brain concerned with emotion, the limbic system. It is characterized by confusion, depression, agitation, anxiety, and memory disturbance. Brain stem encephalomyelitis refers to inflammation of parts of the brain stem and is characterized by double vision, speech disturbance, trouble swallowing, abnormalities of eye movements, hearing loss, and facial numbness. Myelitis is a term used to describe inflammation of the spinal cord and is characterized by weakness, muscle wasting, and involuntary muscle twitches.
Motor neuron disease is a paraneoplastic syndrome characterized by degeneration and inflammation of the nerves innervating voluntary muscle. Accordingly, this syndrome is associated with muscle weakness, muscle wasting, and muscle twitching. It is often difficult to distinguish a "pure" motor neuron disease from one caused by encephalomyelitis.
How are paraneoplastic syndromes treated in a neuro-ICU?
Most paraneoplastic syndromes do not require treatment in a neuro-ICU. However, in some cases, paraneoplastic encephalomyelitis, limbic encephalitis, and neuropathy may be severe enough to be life threatening. These instances are extremely rare. Three general strategies can be undertaken to treat these disorders:
General supportive measures such as intubation can be instituted to ensure that the patient receives an adequate supply of oxygen.
Paraneoplastic syndromes are caused by antibodies directed against the body's nerve cells. Plasmapheresis can be performed to remove pathogenic antibodies, although success is often limited. This process involves removing blood from the body, separating out the cellular elements of the blood, resuspending these cellular elements in a plasma substitute, and then reinfusing this mixture into the body. The purpose of such a procedure is to "cleanse" the blood of anti-tumor antibodies which have become directed against the cells of the nervous system. Immunosuppression with steroids can also be given.
Regardless of the type of syndrome present, these disorders can best be managed by treating the cancer from which the syndrome arises. This is usually accomplished by surgery, radiation therapy, and/or chemotherapy, which is performed once the patient is stable.