Fifty to 80 percent of all amputees experience pain in their stumps or what feels like the missing limbs long after surgical wounds have healed. Now new research from Johns Hopkins suggests the two pains have different sources, bringing us a step closer in understanding what types of drugs might help.
In a study examining stump pain vs. "phantom pain," researchers observed that the powerful pain reliever morphine significantly relieved both stump and phantom pain, while the local anesthetic lidocaine relieved only the stump pain.
"Our results suggest that different therapeutic sensitivities of stump and phantom pain to these drugs exist, and that the mechanisms of these two types of pain may differ," says Srinivasa N. Raja, M.D., lead author of the study and professor of anesthesiology and critical care medicine at Hopkins. The report is to be presented Oct. 16 in New Orleans at the annual meeting of the American Society of Anesthesiologists.
"Overall, the treatment of phantom and stump pain has been disappointing, in part due to the uncertain nature of the mechanisms behind the pain and the lack of well-controlled clinical studies," he says.
Stump pain is believed to arise from nerve injuries at the site of the amputation and the resulting formation of neuromas, noncancerous tumors that grow out of the injured nerve fibers. Phantom pain is thought to reside in the brain. When the part of the brain that controlled the limb before it was amputated no longer has a function, other areas of the brain fill in. The Hopkins data supports that theory, in that lidocaine, a drug that predominantly works on the peripheral nervous system, did not relieve phantom pain. Morphine acts on the peripheral and central nervous systems.
For the study, Raja and his colleagues studied 32 patients with an average age of 54 who had amputated limbs. Twelve patients had pain in the region of the stump, while nine had pain in the missing part of the limb. Eleven patients experienced both types of pain.
On three consecutive days, each patient was given an intravenous injection of either morphine, lidocaine or placebo. Pain measures and patient satisfaction scores were recorded every five minutes from a half-hour before the injection until a half-hour after. The study was double-blind, meaning neither the patients nor the researchers knew which injection was being given.
Patient satisfaction scores were similar and significantly higher for both lidocaine and morphine compared to placebo, which did not significantly reduce either type of pain.
The study was funded by the National Institutes of Health. Other study authors were Christopher L. Wu, M.D.; Peter S. Staats, M.D.; Prabhav K. Tella, M.B.B.S., M.P.H.; and Rachel Vaslav.
Abstract #A-955 "Analgesic Effects of Intravenous Lidocaine and Morphine on Post-Amputation Pain: A Randomized Double-Blind, Active-Placebo-Controlled, Crossover Trial"
Related Web sites:
Johns Hopkins' Department of Anesthesiology and Critical Care Medicine http://www.hopkinsmedicine.org/anesthesiology/
American Society of Anesthesiologists http://www.asahq.org
Materials provided by Johns Hopkins Medical Institutions. Note: Content may be edited for style and length.
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