Darweesh SKL, et al. - This study aimed to investigate whether poor cognitive functioning was associated with an increased risk of parkinsonism. Observations suggested an association of poor cognitive functioning with an increased risk of incident parkinsonism, including probable Parkinson disease (PD). In this study, cognition indicated the probability of parkinsonism over long intervals and extended beyond patients with onset of parkinsonism after dementia. As per findings, cognitive dysfunction could be considered a sign of prodromal PD.

Methods

• From January 8, 2002, to December 14, 2008, 7386 participants of the Rotterdam Study who were free of parkinsonism and dementia were analyzed for baseline cognitive function.
• Researchers administered four tests(Stroop color word test, letter-digit substitution, verbal fluency, and word learning) and derived a global cognition score from principal component analysis.
• Subsequently, they followed up the participants until January 1, 2015, for the onset of parkinsonism through serial in-person examinations and complete access to medical records.
• For this study, parkinsonism was defined as the
• (1) presence of hypokinesia or bradykinesia plus at least 1 other cardinal sign and/or
• (2) clinical diagnosis by a neurologist or geriatrician.
• They considered patients with dementia diagnosis before parkinsonism diagnosis to have probable PD.
• They determined hazard ratios (HRs) for incident parkinsonism per SD decrease in global cognition, adjusted for age, sex, and study subcohort.

Results

• This analysis included 7386 patients; 4236/7386 (57.4%) were women and mean (SD) age was 65.3 (10.2) years.
• During follow-up (median, 8.3 years; range, 0-15 years), 79 (1.1%) individuals received a diagnosis of incident parkinsonism; 57/ 79 (72.2%) received a diagnosis of probable PD.
• Among patients with incident parkinsonism, dementia developed in 24 (10 before and 14 after parkinsonism onset).
• There appeared an association of poor global cognition at baseline with a higher hazard of incident parkinsonism (hazard ratio [HR], 1.79; 95% CI, 1.37-2.33).
• It was noticed that the association remained robust beyond the first 8 years (HR, 1.59; 95% CI, 1.01-2.59) and after removing individuals with dementia onset before parkinsonism (HR, 1.72; 95% CI, 1.28-2.27).
• In addition, there appeared an association of poor global cognition at baseline with incident probable PD (HR, 1.52; 95% CI, 1.11-2.08).
• In this study, letter-digit substitution (HR, 1.59; 95% CI, 1.22-2.04), verbal fluency (HR, 1.61; 95% CI, 1.23-2.08), and inverted interference task Stroop color word test (HR, 1.56; 95% CI, 1.25-1.96) scores were each associated with incident parkinsonism, whereas the association with word learning delayed-task scores was weaker (HR, 1.18; 95% CI, 0.92-1.52).