Early cognitive changes linked to white matter damage in Parkinson’s

By Eleanor McDermid, Senior medwireNews Reporter

Subtle changes in white matter (WM) integrity are detectable in patients with Parkinson’s disease (PD) and are associated with early impairments in cognition, say researchers.

They therefore suggest that imaging of WM could be used as a biomarker for mild cognitive impairment in PD patients.

Early identification of PD patients at risk of developing dementia “is of prognostic importance”, they say, adding that imaging could potentially facilitate therapeutic intervention “early in the disease process before extensive neuronal loss.”

Diffusion tensor imaging revealed significantly increased mean diffusivity among 125 PD patients compared with 50 controls, indicating degeneration of WM. This occurred bilaterally in frontal and parietal subcortical tracts, affecting the forceps minor, cingulum, superior longitudinal fasciculus, inferior longitudinal fasciculus and inferior fronto-occipital fasciculus tracts, the corticospinal tract, the corpus callosum and the internal capsule.

WM degeneration was most marked in PD patients with significant impairments in tests of semantic fluency; they had significantly increased mean diffusivity relative to PD patients with normal cognition, as well as versus controls, which the researchers describe as “a novel finding”.

The PD patients overall had slight but statistically significant impairments in cognition, relative to the controls. For example, the median scores on the Mini-Mental State Examination were 29 versus 30.

Patients with impaired semantic fluency also had reduced grey matter volume in frontal and parietal areas relative both to PD patients with normal cognition and controls, and the same was true for patients with impaired executive function in the Tower of London task. But there were no differences in grey matter volumes between the overall PD group and controls.

Gordon Duncan (Western General Hospital, Edinburgh, UK) and co-researchers stress that reduced mean diffusivity was detectable despite no overall changes in grey matter volume or the directionality of fluid flow in brain matter, assessed via fractional anisotropy.

“Together, these results indicate that degeneration of central WM tracts occurs early in PD and may underlie early cognitive dysfunction”, the team writes in Movement Disorders.

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