BY SARAH OWENS
Older adults who scored poorly on baseline tests of cognitive function had an increased risk of developing parkinsonism or probable Parkinson's disease (PD) over an average eight years of follow-up, according to a new study published online on September 25 in JAMA Neurology.
While research has shown that parkinsonism or PD is associated with an increased risk of cognitive decline, few studies have assessed the relationship between cognitive decline and parkinsonism.
The findings "suggest that poor cognitive functioning can be considered a prodromal sign of PD," the study authors, led by Sirwan K.L. Darweesh, MD. look up title of the department of epidemiology at the Erasmus University Medical Center, in Rotterdam, the Netherlands, wrote.
For the study, researchers at Erasmus University Medical Center assessed data on 7,386 patients who were participating in the Rotterdam Study, a large, prospective, population-based cohort study of the health of older people living in Rotterdam, the Netherlands. All participants were at least 55 years old and did not have parkinsonism or PD at the beginning of the study.
The researchers administered four tests to assess executive function, information processing speed, attention, and semantic fluency. The researchers used the participants' results on the four tests to generate a global cognition score.
During an average 8.3 years of follow-up, the researchers assessed the participants' health records to determine incident parkinsonism or PD. They found that a total of 79 participants (1.1 percent) were diagnosed with parkinsonism, and of these, 57 (72.2 percent) were diagnosed with probable PD.
The researchers found that poor global cognition scores at baseline were associated with a greater risk of incident parkinsonism (hazard ratio [HR], 1.79; 95%CI, 1.37-2.33). The association remained strong even beyond the first eight years (HR, 1.59; 95%CI, 1.01-2.59), and even after the researchers excluded participants who experienced the onset of dementia before parkinsonism (HR, 1.72; 95%CI, 1.28-2.27).
Furthermore, when the researchers examined associations for individual tests, they found that three of the four were associated with incident parkinsonism: the letter-digit substitution (HR, 1.59; 95%CI, 1.22-2.04), verbal fluency (HR, 1.61; 95%CI, 1.23-2.08), and the inverted interference task Stroop color word test (HR, 1.56; 95%CI, 1.25-1.96). However, the association was weaker with word learning delayed-task scores.
The findings, the study authors wrote, suggest that "cognition indicates the probability of parkinsonism over long intervals and extends beyond patients with onset of parkinsonism after dementia." The findings shed light on the prodromal phase of the disease, they added, which could help inform treatment in the early stages of PD.
In an accompanying editorial, Ethan G. Brown, MD, fellow in the department of neurology at the University of California San Francisco School of Medicine, and Caroline M. Tanner, MD, PhD, director of clinical research at The Parkinson's Institute, wrote that the findings "solidify" an association identified in previous studies "in a significantly larger cohort with [more] extensive follow-up," and that "the results are broadly applicable" for treatment of PD and future clinical trials, which should include cognitive impairment as an outcome.
While they noted some limitations to the study, including that the neuropsychological evaluation of cognition was not as thorough as currently recommended, they say the findings mean that physicians should screen for falls and other nonmotor PD symptoms in cognitively impaired patients, and recommend appropriate interventions, such as physical activity.
The researchers noted several study limitations. Among them, misclassifications of parkinsonism were possible, although the researchers limited diagnoses to those given by neurologists or geriatricians; and they considered participants who had a clinical presentation consistent with PD to have probable PD without regard to the onset of dementia.
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