Neuropathic cancer pain: the role of adjuvant analgesics.

Neuropathic pain may be defined as pain related to abnormal somatosensory processing in either the peripheral or central nervous system. This pathophysiologic label is typically applied when the painful symptom is associated with an overt injury to neural structures, is part of a recognized syndrome, or has a dysesthetic quality (usually burning, shooting, or electrical). Most neural injury does not lead to clinically important neuropathic pain, but sometimes even a small degree of tissue injury can precipitate severe pain. In the cancer population, neuropathic pain is often related to compression, direct neoplastic invasion of the peripheral nerves or spinal cord, or to a neuropathy caused by chemotherapy. To manage neuropathic pain in this population, nonopioid adjuvant drugs that are neuroactive or neuromodulatory are often needed to complement opioid therapy. The primary adjuvant analgesics are anticonvulsant and antidepressant medications, but a wide variety of other drugs are also used. To optimize analgesic therapy in patients with neuropathic pain, both opioid and adjuvant analgesics must be used effectively.