LAS VEGAS—If acute pain caused by a damaged peripheral nerve is not cured within six weeks the pain will centralize and a patient will be stuck with it for life, said pain specialist Forest Tennant, MD, DrPH, of the Veract Intractable Pain Clinic in West Covina, California. “Once that pain centralizes, we have no cure. Control is what we have,” Dr. Tennant told attendees at a session titled, “Diagnosis and Management of Central Pain.” “You can’t be too aggressive in treating acute pain because you’ve got a time limit,” he added.
Development of centralized pain begins with injured peripheral nerves and is followed by retrograde chemical or electrical signals that enter the central nervous system and activate glial cells (which are residential macrophages of the nervous system), which in turn causes neuroinflammation. What follows is release of excess glutamate and neurotoxins, cell death, reformation (neuroplasticity), and imprinting of pain sensation.
Once glial cells activate, he said, there is no way to calm them down. Brain cells that have been damaged or destroyed try to regrow. “It is believed that it is in the regrowth process that the pain gets trapped,” he said.
“Centralized pain means central inflammation inside the nervous system, and it can be progressive. It does away with both white matter and gray matter and brain cell volume decreases in these people,” said Dr. Tennant.
Pain centralization usually occurs 6 to 8 weeks after injury, but it also can centralize immediately. In some cases, centralization can be delayed after injury and then occur suddenly. Neck and head injuries, he noted, centralize the worst.
Central pain is characterized by hyperarousal of the autonomic sympathetic nervous system and endocrine system. Signs of a hyperaroused autonomic nervous system include high pulse rate, hypertension, dilated pupils, hyperhidrosis, and vasoconstriction. Elevated adrenocorticotropin (ACTH), cortisol, pregnenolone, dehydroepiandrosterone (DHEA), and testosterone are signs of a hyperaroused endocrine system.
Dr. Tennant noted that there is no generally accepted treatment for central pain, so clinicians may try opioids (including topical), neuropathic agents, antidepressants, bedtime sedatives, anti-inflammatory agents, hormone replacement, stimulants, and anti-anxiety drugs. Diets high in protein are recommended as he has found that patients with central pain eat very little protein. Fish oil supplements and regular exercise are also recommended; the type of exercise is not important. The goal, he said, is to improve blood flow and oxygenation in the brain because oxygen is necessary for the healing process.