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Life expectancy for patients with Parkinson's disease is poorer than some previous studies have suggested, with barely one-third of patients surviving six years with the condition, researchers said.

Among nearly 140,000 Medicare beneficiaries with Parkinson's disease diagnosed in 2002 -- about half of whom were younger than 80 -- 64% had died by 2008, reported Allison W. Willis, MD, and colleagues at Washington University in St. Louis.

This rate was similar to that seen in Medicare patients suffering myocardial infarctions and Alzheimer's disease, and substantially higher than in those diagnosed with congestive heart failure, chronic obstructive pulmonary disease (COPD), or colorectal cancer, the researchers pointed out in Archives of Neurology.

Willis and colleagues also found that the incidence of dementia was common and markedly increased the risk of death in Parkinson's disease, whereas women, Hispanics, and individuals of Asian ancestry were at lower risk of death during the study period.

Geography didn't appear to affect mortality in Parkinson's disease patients with one exception -- those living in urban areas known to have high levels of industrial manganese pollution were at almost 20% higher risk of death than those in low-pollution areas (hazard ratio 1.19, 95% CI 1.10 to 1.29 for areas in the top versus bottom quartile of manganese pollution).

On the other hand, there was no difference in death rates between areas of high and low lead pollution, the researchers indicated.

Willis and colleagues argued that these findings on metals pollution "calls into question whether continued exposure to basal ganglia toxins after symptom onset may accelerate the clinical course of idiopathic Parkinson's disease or be associated with the development of important comorbidities."

In their study, the researchers looked at Medicare records for all patients with claims related to Parkinson's disease in 2002, who lacked such claims in the previous two years. The claims were examined through 2008.

Some 70% of the patients included in the analysis had dementia during the six-year follow-up period, although the records indicated that almost half had clinical evidence of dementia or cognitive impairment before receiving the Parkinson's disease diagnosis.

Among patients with dementia, the hazard ratio for death during the study was 1.72 (95% CI 1.69 to 1.75) after adjusting for age, sex, race, initial dementia status, comorbidities, and socioeconomic deprivation score.

But dementia was not seen equally often among the sexes or ethnic groups, and these patterns were different for mortality.

"The highest frequency of dementia was found in African-American individuals (78.2%) followed by Hispanic individuals (73.1%)," Willis and colleagues wrote, whereas rates among whites and Asians were lower at 69% and 66.8%, respectively.

Blacks also had the highest mortality rates at 66.4%, but whites were a close second at 64.6%. Hispanics and Asians, on the other hand, died at rates of 55.4% and 50.8%, respectively.

Not surprisingly, risk of both death and dementia rose substantially with patients' age.

But the overall six-year mortality rate of 64.4% in Parkinson's disease stood in contrast to rates calculated for the Medicare population on the same basis for conditions more commonly recognized as life-threatening, Willis and colleagues noted. These included:

• Congestive heart failure: 50.9%
• COPD: 44.7%
• Ischemic heart disease: 32.5%
• Stroke or transient ischemic attack: 52.5%

At the same time, the claims data showed that, among some 13,000 Parkinson's disease patients who died in 2006, most received a great deal of healthcare during their terminal year.

Three-quarters were hospitalized at least once and the average number of hospitalizations was 3.4. Infections and cardiovascular disease were the most common reasons cited for these admissions. In only 1% of hospitalizations was Parkinson's disease included among the 10 primary illnesses recorded in patients' charts.

Willis and colleagues suggested that, because most Parkinson's disease patients are not treated by neurologists, the doctors they do see may spend most of the visits managing the Parkinson symptoms and not enough on patients' other conditions.

Moreover, some symptoms of cardiovascular disease, infections, and other disorders, such as fatigue and weakness, may mistakenly be attributed to Parkinson's disease.

"Future studies investigating specific ways by which specialist care reduces Parkinson's disease mortality would be valuable," the researchers wrote.

They also asserted that their finding of an association between manganese pollution and mortality risk is another in a line of studies implicating environmental toxins in Parkinson-related neurodegeneration.

The same group had previously reported that Parkinson's disease incidence was highest in counties with high versus low levels of industrial manganese pollution (Am J Epidemiol 2010; 172: 1357-1363.)

Willis and colleagues also cited another study finding that Parkinson risk was increased in areas exposed to a manganese-containing herbicide called maneb (Am J Epidemiol 2009; 169: 919-926).

Limitations to the study include possible errors and omissions in Medicare data as well as the possibility of different healthcare-seeking behaviors in various populations and other unmeasured confounders.

The researchers also lacked data on lifetime exposures to manganese and other pollutants, relying instead on recent pollution levels in beneficiaries' current residences.

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