Poor Cognitive Functioning Linked to Risk of Parkinsonism

Poor cognitive functioning is associated with a higher risk for incident parkinsonism, including probable Parkinson disease (PD), according to a recent study.

Cognitive dysfunction is common among patients with parkinsonism, including PD. However, little is known about cognitive functioning prior to a parkinsonism diagnosis, during which patients may still respond to putative disease-modifying interventions.
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For the Rotterdam Study, the researchers assessed the baseline cognitive functioning of 7386 patients free of parkinsonism and dementia from January 8, 2002, to December 14, 2008. Follow-up lasted until January 1, 2015. Mean patient age was 65.3 years, and 57.4% of patients were women

The Stroop color word test, letter-digit substitution, verbal fluency, and word learning tests were administered to patients, and principal component analysis was used to calculate a global cognition score. Patients were subsequently assessed via serial in-person examinations and medical records over the course of follow-up for the onset of parkinsonism.

The researchers defined parkinsonism as the presence of hypokinesia or bradykinesia plus at least 1 other cardinal sign and/or clinical diagnosis by a neurologist or geriatrician. Patients with a diagnosis of dementia prior to receiving a parkinsonism diagnosis were considered to have probable PD.

The main outcome of the study was hazard ratios (HRs) for incident parkinsonism per SD decrease in global cognition. Results were adjusted for age, sex, and study subcohort.

Throughout follow-up, 79 (1.1%) patients received a diagnosis of incident parkinsonism, of whom 57 (72.2%) also received a diagnosis of probable PD. Of those with incident parkinsonism, 24 (30.4%) also developed dementia, of whom 10 developed dementia before the onset of parkinsonism, and 14 developed dementia after.

The researchers found that poor global cognition at baseline was associated with an increased risk of incident parkinsonism, with this association remaining robust beyond the first 8 years and after removing patients with dementia onset before parkinsonism. Poor global cognition at baseline was associated with incident probable PD.

Furthermore, letter-digit substitution, verbal fluency, and inverted interference task Stroop color word test scores were each associated with incident parkinsonism. However, the association of word learning delayed-task scores with incident parkinsonism was weaker.

“Poor cognitive functioning is associated with an increased risk of incident parkinsonism, including probable PD,” the researchers concluded. “Cognition indicates the probability of parkinsonism over long intervals and extends beyond patients with onset of parkinsonism after dementia. The findings suggest that cognitive dysfunction can be considered a sign of prodromal PD.”

—Christina Vogt

Reference:

Darweesh SKL, Wolters FJ, Postuma RB, et al. Association between poor cognitive functioning and risk of incident parkinsonism: the Rotterdam Study [Published online September 25, 2017]. JAMA Neurol. doi:10.1001/jamaneurol.2017.2248.