Parkinson’s cognitive issues hit 1 in 3, highlighting screening need

Cognitive issues affect about one in three people with Parkinson’s disease, a meta-analysis found, highlighting the importance of early screening and long-term research into the causes and early indicators of cognitive decline in patients.

The researchers cautioned that the studies they looked at varied widely in diagnostic criteria and design, and cautioned that this estimate should not be interpreted as an exact rate for any population. Still, they said, they found “clinically meaningful signals that warrant further investigation.”

Older patients and those who experience low blood pressure when standing or have other conditions such as diabetes are more likely to be affected, according to the study, “Cognitive impairment in Parkinson’s disease: prevalence and associations with cardiometabolic, vascular, and autonomic factors — a systematic review and meta-analysis,” published in npj Parkinson’s Disease.

Parkinson’s is best known for its motor symptoms, but it can also affect cognitive abilities, including memory, reasoning, and problem-solving. However, the prevalence of cognitive impairment and the factors that make someone more likely to develop it are unclear.

To estimate the prevalence of cognitive impairment in Parkinson’s and to identify predisposing factors, the researchers searched medical databases and identified 39 studies that met their criteria. They found 16 additional studies through manual searches of other sources. In total, 55 studies involving more than 100,000 individuals were combined in a meta-analysis.

Twenty-five of the 55 studies looked at Parkinson’s dementia, meaning severe cognitive impairment that interferes with daily life. Fourteen focused on mild cognitive impairment (MCI) in Parkinson’s, meaning noticeable problems with cognitive abilities that are not severe enough to be classified as dementia.

Researchers note need for caution in interpreting results

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Overall, 51 studies involving 93,659 individuals provided data for estimating prevalence. The combined estimate showed that nearly one-third of patients (32.7%) had cognitive impairment.

The estimated prevalence varied depending on how Parkinson’s was diagnosed and how cognitive abilities were measured. Studies using Movement Disorder Society (MDS) criteria reported higher rates than studies using other criteria. The rate was also higher for MCI (52.7%) than for broader cognitive impairment (24.8%) and Parkinson’s dementia (24%).

Age alone did not explain most of the differences between studies. The prevalence was similar in studies of patients aged 65 or older and those involving patients younger than 65 (34.4% vs. 32.2%). Prevalence was also broadly similar in community-based and hospital-based studies (29% vs. 33.4%). Larger studies tended to report lower rates than smaller studies.

Patients with orthostatic hypotension, which refers to sudden low blood pressure when standing up, were 2.18 times more likely to develop cognitive impairment than patients without orthostatic hypotension. Metabolic syndrome, a combination of conditions such as high blood pressure, abnormal blood sugar, and unhealthy cholesterol levels, was also associated with cognitive impairment.

Diabetes was associated with cognitive impairment in several types of analysis. High blood pressure, being overweight, dyslipidemia (abnormal levels of fats in the blood), and current alcohol use also showed associations in some analyses. Obesity, being underweight, high blood sugar, coronary artery disease, and current smoking were not.

“Our analysis identified several clinically relevant correlates, particularly orthostatic hypotension, diabetes, hypertension, and metabolic syndrome, although the certainty of evidence remained limited because of the observational nature and methodological variability of the available literature,” the researchers wrote.

Indeed, when using meta-regression to understand why results differed between studies, they found that the type of cognitive impairment and the diagnostic criteria for Parkinson’s helped explain some of the differences.

The substantial differences across studies suggest that diagnostic criteria and study design are important when interpreting prevalence estimates, the researchers said.