To investigate factors affecting survival in PD, Willis and colleagues searched nationwide Medicare claims data from 2002, identifying more than 138,000 Americans with PD whom they followed through 2008. This represents the largest such cohort studied to date and, since Medicare is used by nearly all Americans 65 or older, the sample should reflect the general population, the authors note. The six-year death rate for people with PD was almost four times higher than that in the general elderly population. Notably, the PD death rate equated to that seen for heart attacks, Alzheimer’s disease, and hip fractures. (Hip fractures are particularly devastating for elderly people due to the associated complications and loss of mobility.) The PD death risk was slightly lower in women, Asians, and Hispanics compared to white and African American men.

Having dementia nearly doubled the death risk. About 70 percent of the PD patients in the study had dementia, compared to a nationwide dementia prevalence of around 15 percent for people over 70 (see Plassman et al., 2007). Previous estimates of dementia prevalence in PD had varied from about 25 to 90 percent. Parkinson’s disease frequently progresses to Parkinson’s dementia (see, e.g., ARF related news story), but people with PD may also get other dementias such as AD or vascular dementia. Although the Medicare data does not distinguish dementia type, in this cohort more women and African Americans were diagnosed than other groups, mirroring AD demographics and suggesting that at least some of the cases might be due to AD, the authors observe. The finding highlights the importance of screening for dementia in people with PD and taking preventive measures, Willis said. For example, undertreated heart disease could lead to vascular dementia.

Additionally, the authors found that PD patients living in urban areas with high industrial manganese output had about 20 percent higher death risk than those in low-manganese counties. In a previous study, Racette’s group reported abnormalities in the dopaminergic system in welders, who are occupationally exposed to manganese (see ARF related news story on Criswell et al., 2011), implying the metal could be a risk factor for PD. “We should probably start thinking about how environmental exposures to all kinds of pollutants can affect disease progression,” Willis said. In ongoing work, she is setting up a large prospective study that will collect data on several types of pollution exposure in PD patients and correlate this with disease progression.

“The good thing about these types of studies is that they generate a lot of questions,” said Jane Ann Driver at Brigham and Women’s Hospital, Boston, Massachusetts. She was not involved in the study. Driver is particularly intrigued by the link to manganese toxicity. “We don’t know what causes most cases of PD, so anything that sheds light on a risk that hasn’t been appreciated before, and is potentially reversible, is important.”

Driver noted that, because PD affects so many aspects of health (see, e.g., ARF related news story), it makes sense that people with the disease are more susceptible to infections and other complications. The study raises the question of whether cardiovascular problems are underdiagnosed or undertreated in PD patients, Driver said. For their part, the authors speculate that symptoms of heart trouble such as fatigue or weakness could be mistaken for PD symptoms and overlooked. Willis suggested that people with Parkinson’s may need extra time with their physician to make sure their basic health is being managed as well as possible.—Madolyn Bowman Rogers.

Reference:
Willis AW, Schootman M, Kung N, Evanoff BA, Perlmutter JS, Racette BA. Predictors of survival in patients with Parkinson disease. Arch Neurol. 2012 Jan 2. Abstract