Parkinson’s Disease Increased Over 30-Year Period, Study Shows

The incidence of Parkinson’s disease (PD) and parkinsonism increased significantly in the 30 years from 1976 to 2005, according to a Mayo Clinic study published in JAMA Neurology titled “Time Trends in the Incidence of Parkinson Disease.” Researchers say the trend was particularly strong in men aged 70 and older.

To explore secular trends concerning the incidence of parkinsonism (any condition that causes a combination of the movement abnormalities seen in Parkinson’s disease) and Parkinson’s over 30 years in an American population, researchers used the Rochester Epidemiology Project for the medical records of anyone in Olmsted County, Minnesota, to identify cases of Parkinson’s and other types of parkinsonism from 1976 to 2005. All clinical cases were classified by an expert in movement disorders using specific criteria.

Of 906 patients identified with parkinsonism, 501 were men, with a median age of disease onset of 74 years. Of the 464 identified patients with Parkinson’s, 275 were men, with a median onset of the disease at 73 years.

The results showed that for both parkinsonism and Parkinson’s disease male patients, overall incidence rates significantly increased over the 30 years. Specifically, men of all ages had a 17 percent higher risk of developing parkinsonism and a 24 percent higher risk of developing Parkinson’s disease for every 10 calendar years.

These trends were primarily driven by older patients. Particularly for men aged 70 or older, there was an increase in the incidence rates for both parkinsonism and Parkinson’s disease, with the results showing a 24 percent higher risk of developing parkinsonism and a 35 percent higher risk of developing Parkinson’s disease for every 10 calendar years.

“We have reasons to believe that this is a real trend,” Rodolfo Savica, M.D., Ph.D., lead author and neurologist at Mayo Clinic, said in a recent news release. “The trend is probably not caused merely by changes in people’s awareness or changes in medical practice over time. We have evidence to suggest that there has been a genuine increase in the risk of Parkinson’s disease.”

The researchers point to environmental and lifestyle changes as potential causes for the increase. “There has been a dramatic change in exposure to some risk factors in the United States,” Savica said. “We know that environmental agents like pesticides or smoking or other agents in the environment have changed in the last 70 years or so. Changes in exposure to a number of risk factors may have caused Parkinson’s disease to rise.”

This is the first study considering long-term trends in risk over 30 years and provides contrary evidence to two previous U.S. studies and one Canadian study in which the results revealed no trend, and is also contrary to three studies conducted in the United Kingdom indicating a decline in Parkinson’s disease incidence over time.

The Mayo Clinic study also revealed there was an increased risk for both men and women born in the 1920 cohort (1915-1924), but this effect was significant only for Parkinson’s disease and only in men.

“This observation is important because the persons born in that particular decade may have been exposed to some environmental or other factors during their intrauterine life or early after birth that increased the risk,” Savica said. “We need to confirm this hypothesis.

Parkinsonism includes Parkinson’s disease, but may include other disorders. The diagnosis of parkinsonism requires slowness of movement and at least one other symptom, such as muscle rigidity, a tendency to fall, or a tremor while a person is at rest. Parkinson’s disease has the manifestations of parkinsonism, but without any other known causes, and it is the most common type of parkinsonism.

These trends may be related to changes in smoking behavior over the second half of the 20th century as well as other environmental and lifestyle changes. However, the trends could be unauthentic and need confirmation in other populations, the researchers said, urging caution in interpreting the study results.

“Parkinson’s disease is an important disease and a cause of disability, especially in older ages, and we don’t want to have people untreated for a condition that is treatable just because they have four or five other diseases that are more prominent,” Savica said.

The fact that time trends were found to be more pronounced in men than in women may support a real incidence trend. The recognition of symptoms in the context of multiple illnesses should have altered over time in men and women, the researchers noted.

“Differences in men and women may be important in understanding the environmental causes of Parkinson’s disease,” Savica said.

If there is a genuine increase in the incidence trend and if these results can be replicated in other clinical populations, it may hold important implications for research into the causes of Parkinson’s and for public health, the researchers concluded.