At eight years after implantation of a subthalamic nucleus deep brain stimulation (STN DBS) device, pain is lessened or eliminated, compared with baseline, among patients with Parkinson’s disease, according to research published online ahead of print March 23 in JAMA Neurology. Most patients developed new pain after implantation, however, most of which was musculoskeletal. The results indicate that clinicians should treat musculoskeletal pain independently, researchers said.
Beom S. Jeon, MD, PhD, a neurologist at the Seoul National University Hospital in South Korea, and colleagues evaluated the long-term effect of STN DBS on pain in 24 patients with Parkinson’s disease. Assessments of pain were conducted preoperatively and eight years after surgery. Thirteen patients had additional two-year postoperative data.
The 24 patients (15 men) underwent STN DBS at the Movement Disorder Center at Seoul National University Hospital from June 1, 2005, through March 31, 2006. The inclusion criteria for STN DBS were a clinical diagnosis of idiopathic Parkinson’s disease, levodopa responsiveness with severe motor complications, absence of severe dementia, and normal findings on brain MRI.
Motor symptoms were assessed using the Unified Parkinson’s Disease Rating Scale (UPDRS) and the Hoehn and Yahr staging scale. Pain severity was scored on an ordinal scale from 0 (absent) to 10 (maximal) in seven parts of the body (ie, head, neck, trunk, and the upper and lower extremities on each side of the body). Pain quality was categorized as dystonic, musculoskeletal, radiculoneuritic, or central.
New Pain Developed in 75% of Patients
Of the 24 patients, 16 (67%) had pain at baseline when not taking medication, with an average pain score of 6.2. All off-medication baseline pain lessened or disappeared at eight years after surgery. New pain developed, however, in 18 of 24 patients (75%) during the eight-year follow-up, including in five patients who had had no pain at baseline. The average pain score for new pain was 4.4.
The most common body parts with newly developed pain were the lower extremities, followed by the upper extremities. The types of new pain at eight years were musculoskeletal in 11 patients, central in four patients, radiculoneuritic in three patients, and dystonic in one patient.
Overall, the number of patients with off-medication pain increased from 16 at baseline to 20 at eight years. The number of body parts with pain increased from 48 to 60, while average pain scores decreased from 6.2 to 4.8.
“The results of the present study highlight once again that musculoskeletal problems should be considered when predicting the operative outcome before surgery, and continuous evaluation and treatment of musculoskeletal pain should be performed after surgery,” Dr. Jeon and colleagues said.
Average off-medication dystonic pain score increased from 6.3 at baseline to 8.5 at eight years, but the eight-year score was the average score of two patients who had severe dystonic pain because of rigidity, the authors said. In all, the number of patients with dystonic pain decreased from five to two. Average off-medication pain scores decreased by 55% for radiculoneuritic pain, 44% for central pain, and 29% for musculoskeletal pain.
Lack of Control Group Among Study’s Limitations
The small number of patients in the study and the lack of a control group treated medically were among the study’s limitations, the authors said. The study also did not evaluate the association between motor UPDRS scores and pain, and it did not measure patients’ overall level of pain, they said.
Despite the study’s limitations, the long follow-up period “provides a novel perspective on the durability of the pain-relieving properties of STN DBS in Parkinson’s disease,” said Richard B. Dewey Jr., MD, Professor of Neurology and Neurotherapeutics, and Pravin Khemani, MD, Assistant Professor of Neurology and Neurotherapeutics, both at the University of Texas Southwestern Medical Center in Dallas, in an accompanying editorial.
“The authors direct our attention to the fact that musculoskeletal pain may emerge years after DBS, warranting individualized treatment. … Although there is a growing consensus that STN DBS decreases the level of pain in people with Parkinson’s disease, the literature is mixed on the subtypes of pain that are responsive to DBS, and the study by Jung and colleagues shows that new pain arising years after the procedure is common,” they continued.
The next step for researchers is to seek a deeper understanding of the mechanism of pain in Parkinson’s disease. Future trials with larger cohorts, longer observational periods, and standard methods will enable effective interpretation of outcomes, concluded Drs. Dewey and Khemani.
—Jake Remaly
