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Plexopathies
Cervical, brachial, and lumbosacral plexi can be sources of intractable pain in cancer patients.131 Pain is produced when these structures are infiltrated by tumor or compressed by fibrosis after radiation therapy to adjacent structures. Pain tends to be less prominent in radiation-induced plexopathies than in tumor-related ones. Traction injury related to the positioning of a patient during a prolonged operation may also produce brachial plexopathy.
Pain originating in the cervical plexus often occurs as an aching discomfort that may radiate into the neck and occiput. It is most commonly caused by metastasis to the cervical lymph nodes or the local extension of primary head and neck tumors.
Brachial plexopathy is a common complication of lung cancer and lymphoma, but it can also be caused by metastasis to the brachial plexus from a remote primary tumor.263 Pain occurs in up to 85 percent of patients with brachial plexus involvement and may precede weakness or sensory loss by months.159 When the upper plexus is damaged by tumor, pain usually begins in the shoulder and is associated with shooting or electrical sensations in the thumb and index finger. When the lower plexus is involved, as is more common, pain begins in the shoulder and radiates into the elbow, arm, and medial forearm, and into the fourth and fifth digits. In about 25 percent of patients, both upper and lower divisions are involved. Compared with tumor-related plexopathy, radiation damage to the brachial plexus causes less severe pain, distributed initially in the upper division.
Epidural extension may occur in up to 50 percent of patients with superior pulmonary sulcus ("Pancoast") tumors.247 Epidural disease is more likely to occur when the entire plexus is involved and Horner's syndrome is present, which indicates medial and paraspinal spread of tumor. Lymphoma may produce brachial plexopathy and spinal cord compression in the absence of vertebral body erosion. CT and MRI of the brachial plexus and epidural spaces are the diagnostic procedures of choice, and are essential to define the extent of disease and to determine the appropriate radiation ports.
The lumbosacral plexus, embedded in the psoas muscle, may be invaded by tumors of the abdomen and pelvis. Colorectal, endometrial, and renal cancers, as well as sarcomas and lymphomas, may invade this plexus by direct spread. However, 25 percent of lumbosacral plexopathies are metastatic.321 Pain is usually felt in the lower abdomen, buttock, and leg. Infiltration of the sacral plexus may produce perineal and perirectal pain, which is exacerbated by sitting and lying prone. Pain typically precedes, by weeks or even months, the necrologic signs of weakness, sensory loss, or urinary incontinence. Abdominal and pelvic CT or MRI may provide the diagnosis and allow definition of radiation portals. Similar to patients with brachial plexopathy, patients with diffuse or bilateral lumbosacral plexus involvement may have an epidural extension of tumor, in which case, MRI of the epidural space is also required. Epidural disease of the cauda equine or leptomeningeal tumor may produce a clinical syndrome similar to lumbosacral plexopathy.131
Note: Pain may precede overt necrologic signs in spinal cord compression, plexopathies, and spinal metastasis. Prompt recognition of these syndromes and institution of appropriate treatment can avoid paralysis and incontinence.
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