Parkinson’s disease starts when nerve cells in the brain become impaired and gradually die. As these cells die, people with the disease may notice a tremor in a hand. Later, they may develop involuntary shaking elsewhere, muscle stiffness, slowed movements, problems with balance, and other symptoms. As a result, it may become difficult to get dressed, talk, and walk. Although treatment with medicines or surgery can help with these symptoms, there are no methods to cure or slow progression of the disease.

One possible reason that scientists haven’t yet found ways to slow the progression of Parkinson’s disease might be that promising medicines were tested too late in the disease process. In previous work, a research team led by Dr. Brad A. Racette at Washington University School of Medicine developed a computer model to identify people with undiagnosed Parkinson’s disease using U.S. Medicare claims data. The model correctly predicted that people who were treated for early disease symptoms suchas falling were more likely than others to be diagnosed with Parkinson’s disease.

To add another dimension to their model, the researchers examined Medicare prescription data. The team’s previous analyses had suggested that people with autoimmune diseases, in which the immune system mistakenly attacks the body’s own tissues, had a lower risk of developing Parkinson’s disease. Suspecting that the drugs used to treat these diseases might play a role, they explored the possible links between drugs that suppress the immune system and the diagnosis of Parkinson’s disease. The study was supported in part by NIH’s National Institute of Environmental Health Sciences (NIEHS) and National Institute of Neurological Disorders and Stroke (NINDS). Results appeared onlineon May 31, 2018,in theAnnals of Clinical and Translational Neurology.

The researchers used claims data for more than 48,000 people, aged 65 to 90, who were newly diagnosed with Parkinson’s disease in 2009. The control group was more than 52,000 randomly selected adults who had not been diagnosed with Parkinson’s disease. The team examined the use of 26 immune-suppressing drugs belonging to six categories. The uses of these drugs include fighting inflammation and helping prevent the body from rejecting donor organs.

The researchers found a substantially lower risk of developing Parkinson’s disease among people who used either of two categories of immune-suppressing drugs: corticosteroids (about 20% lower) or inosine monophosphate dehydrogenase inhibitors (about 36% lower). For people who took both, the risk of the disease was even lower. Four other categories of immune-suppressing drugs did not show as much change in risk.

These findings suggest that the immune system may play a role in the development of Parkinson’s disease in older adults. By dampening the immune system, certain drugs may lower the risk of the disease. However, further study will be needed to confirm these findings.

“It’s a reasonable assumption that if a drug reduces the risk of getting Parkinson’s, it also will slow disease progression, and we’re exploring that now,” Racette says. “Our next step is to conduct a proof-of-concept study with people newly diagnosed with Parkinson’s disease to see whether these drugs have the effect on the immune system that we’d expect.”

—by Geri Piazza