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Direct vs. Remote (paraneoplastic) Effects of Tumors

Signs and symptoms of nervous system tumors are generally caused by their localized neuronal destruction and/or space-occupying effects with consequent brain compression or displacement -- these are DIRECT effects. REMOTE or paraneoplastic effects of tumors refer to changes in the peripheral or central nervous system caused by a primary tumor elsewhere in the body. This section will first describe paraneoplastic effects (or syndromes), and then discuss the many types of direct effects of a tumor within the skull.

A. Paraneoplastic Syndromes (Remote Effects)  

Remote effects of a neoplasm involve changes in the peripheral or central nervous system caused by a primary tumor elsewhere in the body, sometimes before clinical recognition of the primary neoplasm. Paraneoplastic syndromes are more common with certain primary neoplasms - the most common tumor causing paraneoplastic syndromes is small cell carcinoma of the lung. Peripheral nerves, muscle, dorsal root ganglia or CNS structures may be involved. CNS syndromes that have been recognized include paraneoplastic cerebellar degeneration, limbic encephalitis, and subacute sensory neuropathy. Most or all paraneoplastic neurologic disorders are immune-mediated. One mechanism involves production of autoantibodies associated with the tumor which cross-react with antigens in the nervous system to produce different clinical syndromes.