Cancer and the Peripheral Nervous System

Cancer can directly involve any part of the neuromuscular system, including the spinal neurons and nerve roots, the brachial and lumbosacral plexus, the peripheral nerves, and muscles. Brachial Plexopathy Brachial plexopathy can result from metastases to the axillary or supraclavicular nodes, from primary tumor invasion or rarely, in the case of breast carcinoma, from hematogenous spread. About 4% of lung and 2% of breast cancers cause symptomatic tumor infiltration of the brachial plexus followed in frequency by lymphomas. Relentlessly progressive pain is the presenting feature in most patients, usually in the shoulder and axilla radiating to the medial arm, forearm, and the fourth and fifth fingers (1). Weakness and sensory loss follows after a variable period, involving the C8/T1 roots in most patients. In the remaining cases, there is diffuse and often patchy plexus infiltration. Carcinomatous involvement of more than one root is almost always the case and should help in the distinction from degenerative disc disease. Almost half of patients have unilateral Horner’s syndrome as well as tumor spread to the adjacent epidural space, both features helping to distinguish tumor involvement of the plexus from radiotherapy-induced damage. The differential diagnosis includes, besides radiation plexopathy (Table 1), rare entities such as paraneoplastic plexopathy associated with lymphomas and toxicity from chemotherapy (2).