Functional connectivity loss may underlie Parkinson’s cognitive decline

By Eleanor McDermid, Senior medwireNews Reporter

Patients with Parkinson’s disease (PD) have deceases in functional connectivity over time and these correlate closely with cognitive decline, research shows.

For the study, Kim Olde Dubbelink (VU University Medical Center, Amsterdam, the Netherlands) and co-workers used resting-state functional magnetic resonance imaging (RS-fMRI) to assess 36 PD patients, aged an average of 65.8 years with an average disease duration of 9.24 years, and 12 matched controls.

Their findings “strengthen the idea that a loss of resting-state functional connectivity between brain areas is an important pathophysiologic factor in PD-related cognitive decline”, they write in Neurology.

When measured at baseline, the PD patients had significant and widespread reductions in functional connectivity, relative to controls. Affected regions included the middle frontal gyrus, precentral gyrus and postcentral gyrus and the superior, middle and inferior occipital gyrus.

Three patients had dementia at baseline, and an additional six developed the condition over the subsequent 3 years. The average scores of all the PD patients on the Cambridge Cognitive Examination (CAMCOG) scale fell significantly, from 94.7 to 91.1, whereas scores among the controls remained stable.

At the 3-year reassessment, connectivity in controls was similar to that at baseline. By contrast, the PD patients had significant declines in the precentral gyrus and postcentral gyrus, and the superior, middle and inferior occipital gyrus, among other regions.

Declines in functional connectivity, most particularly in the paracentral lobule, the superior parietal cortex and occipital brain regions, significantly correlated with decreases over time in patients’ cognitive function on the CAMCOG scale.

This relationship was independent of patients’ motor function scores on the Unified Parkinson’s Disease Rating Scale. However, the reverse was not true; the slight correlation between connectivity declines and motor function scores disappeared after accounting for CAMCOG scores.

In an editorial accompanying the study, Hitoshi Shinotoh (National Institute of Radiological Sciences, Chiba, Japan) and Alessandro Tessitore (Second University of Naples, Italy) say: “Although the translation of RS-fMRI to clinical practice is incomplete, this study provides novel clues on the neural substrate of progressive cognitive decline in PD.

“Therefore, it will be interesting and important to ascertain whether a specific functional connectivity pattern may represent an early marker of dementia in PD.”

They add that the decline in connectivity seen in the occipital regions is in keeping with previous studies “that showed diminished glucose metabolism and cholinergic neurotransmission in the occipital lobe of patients with PD and PD-related dementia.”

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