Worsening or uncontrolled Parkinson's disease symptoms were also seen more commonly in the surgery group.
In an accompanying editorial, Dr. Maria Rodriguez-Oroz of the University of Navarra in Pamplona, Spain, raised a number of methodological complaints about the study: its open-label design, lack of patient diaries on motor abilities, and definitions of the "on" state that were left to individual clinicians' judgment.
She also lamented that the report only mentioned serious adverse effects. "Information on non-serious adverse events would have been relevant for neurologists in their day-to-day treatment of patients with Parkinson's disease," she wrote, especially with respect to the apomorphine infusions that many patients in both groups relied on during the study.
On the other hand, she noted that the study was larger than other trials of deep brain stimulation in Parkinson's disease.
The trial's real value, Rodriguez-Oroz suggested, may emerge with additional follow-up of the patients, which Williams and colleagues plan to continue for nine years.
"This will provide invaluable information about the long-term benefit of surgery, especially in different subgroups of patients" defined by age, disease severity, and other parameters that could influence outcomes, Rodriguez-Oroz wrote.