In a small study of patients with Parkinson's disease, treatment with deep brain stimulation was more effective than drug therapy in improving their sense of smell (olfaction), which is often impaired with the neurological condition. This finding supports the belief that deep brain stimulation may improve both movement and non-movement symptoms of the disease.

This study is not the first to examine the impact of deep brain stimulation on olfaction in Parkinson's disease patients, lead researcher Mary Linton B. Peters, from the University of Massachusetts Medical School, Worcester, told Reuters Health. However, it is new in that it compares patients on routine medical therapy to patients who undergo a surgical procedure. "This provides a useful comparison between therapeutic choices and their longer-term effects vs. short-term acute effects."

Peters presented her team's findings last week at the American Association of Neurological Surgeons annual meeting in San Diego, California.

The study included 9 patients with Parkinson's disease who underwent bilateral subthalamic nucleus deep brain stimulation, 36 patients on medical therapy, and 44 healthy control subjects. Olfaction was evaluated using the University of Pennsylvania Smell Identification Test, which includes 40 different odors.

"We found that deep brain stimulation-treated patients had better olfaction than those treated medically, despite having more non-motor symptoms overall," Peters said. "This was not an acute effect, but rather seems to be due to longer-term effects of stimulation."

There was no evidence that a high dose of a particular medication led to better or worse olfaction than a low dose.

Peters said that her group is now involved in a functional imaging study to better understand the mechanisms underlying the impairments in smell among Parkinson's disease patients. "We hope this will help us understand why patients lose their sense of smell, and perhaps serve as an early diagnostic tool for Parkinson's disease."