Cancer can affect peripheral nerves either by compression or direct invasion. Direct invasion occurs either from hematogenous spread of tumor to peripheral nerves or dorsal root ganglia or by direct extension to nerve from surrounding structures. Typically, head and neck malignancies, melanoma, lung and breast cancer, and abdominal and pelvic tumors cause either cranial or peripheral nerve dysfunction. Occurring either early or late in the disease process, the clinical signs and symptoms are reflective of the anatomical sites and nerves involved. Frequently pain, sensory symptoms, or weakness are manifested by involvement of either single or multiple cranial nerves, spinal roots, nerve plexi, or peripheral nerves. Complications of therapy including radiation fibrosis and chemotherapy-induced neuropathy can mimic peripheral nerve metastases. Acute ischemic or inflammatory neuropathies and complications of paraneoplastic neurological syndromes should also be considered. Diagnosis may be challenging, requiring frequent neuroimaging studies of the appropriate area. Either CT or MRI of the appropriate area is performed in an attempt to either delineate discrete tumors or areas of enhancement. If imaging studies fail to reveal the presence of tumor, exploration of the affected area may be recommended depending on extent of the underlying malignancy, degree of patient's disability, and surgical accessibility and morbidity. Control of pain, which is frequently severe and unrelenting, is a priority. This control may be achieved with systemic chemotherapy or focal radiation. Additionally, pain control with analgesics or anesthetic blocks may be successful. The extent and response of the underlying tumor to therapy and severity of pain portends the prognosis.
Goetz: Textbook of Clinical Neurology, 1st ed., Copyright © 1999 W. B. Saunders Company
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