By Steven Reinberg
MONDAY, March 23, 2015 (HealthDay News) -- People with Parkinson's disease who undergo deep brain stimulation may experience long-term pain relief, a small, new study from Korea suggests.
However, three-quarters of the patients developed new pain in muscles and joints eight years after the procedure was performed, the researchers found.
"It is potentially important that some pain types improved, but also important to understand why other types of pain did not benefit from stimulation," said Dr. Michael Okun, national medical director for the National Parkinson Foundation.
Dr. Michael Schulder, vice chairman of neurosurgery at North Shore University Hospital in Manhasset, N.Y., said that pain is common among these patients.
"There is little doubt that pain is one of the problems associated with Parkinson disease," he said. "But it is not completely understood whether it is related to stiffness or to abnormal mechanisms in the brain. In addition, depression and other psychological problems may have a role," Schulder said.
The question the study leaves unanswered is why patients developed new pain, Schulder said. "The original pain got better, but they got new pain, so in the end it's kind of a wash. But they might have been in more pain if they didn't have the deep brain stimulation," he noted.
Deep brain stimulation involves surgically implanting a battery pack called a neurostimulator in the brain. This sends out tiny electrical pulses to targeted areas of the brain, to block signals that cause the tremors and other motor symptoms of Parkinson's, according to the foundation.
While this and other advances have helped ease movement problems associated with the disorder, less has been done to understand the debilitating pain associated with Parkinson's, experts say.
"This study draws attention to an important and often neglected area of Parkinson disease care and research," Okun said.
Typically, pre-existing pain and its response to deep brain stimulation therapy is not measured, he explained.
Pain that starts after the implantation surgery also needs to be studied, Okun added, noting it is likely related to the disease itself and other medical conditions.
This latest study was published online March 23 in the journal JAMA Neurology.
A team led by Dr. Beom Jeon, from the Seoul National University Hospital, studied the long-term effects of deep brain stimulation on pain in 24 Parkinson patients. The researchers measured patients' pain before surgery and eight years later.
Sixteen of the patients experienced pain before surgery when not taking medication. Their average pain score was 6.2 on a scale of 1 to 10 where 10 represents the most pain, the researchers reported.
Jeon's team found that the pain suffered before surgery had improved or disappeared eight years later.
But 18 patients developed new pain during the follow-up period.
New pain affected 47 body parts, with an average pain score of 4.4. For more than half of these patients, the new pain was described as aching and cramping in joints or muscles, the researchers said.
This new muscle pain needs to be researched separately, the researchers said, noting it didn't seem to respond to deep brain stimulation.
"We found that pain in [Parkinson's disease] is improved by deep brain stimulation, and the beneficial effect persists after a long-term follow-up of eight years," the researchers concluded.
"In addition, new pain developed in most of the patients during the eight-year follow-up period. We also found that deep brain stimulation is decidedly less effective for musculoskeletal pain and [that pain] tends to increase over time. Therefore, musculoskeletal pain needs to be addressed independently," the researchers concluded.
The authors of an accompanying editorial said larger trials are needed with longer follow-up. "For now we have learned that [deep brain stimulation] does not take the ouch out of [Parkinson disease]," they wrote.