Regional Multiple Pathology Scores Are Associated with Cognitive Decline in Lewy Body Dementias

Abstract

Dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD) are characterized by the presence of α-synuclein-containing Lewy bodies and Lewy neurites. However, both dementias also show variable degrees of Alzheimer's disease (AD) pathology (senile plaques and neurofibrillary tangles), particularly in areas of the cortex associated with higher cognitive functions. This study investigates the contribution of the individual and combined pathologies in determining the rate of cognitive decline. Cortical α-synuclein, phosphorylated tau (phosphotau) and Aβ plaque pathology in 34 PDD and 55 DLB patients was assessed semi-quantitatively in four regions of the neocortex. The decline in cognition, assessed by Mini Mental State Examination, correlated positively with the cortical α-synuclein load. Patients also had varying degrees of senile Aβ plaque and phosphotau pathology. Regression analyses pointed to a combined pathology (Aβ plaque plus phosphotau plus α-synuclein-positive features), particularly in the prefrontal cortex (BA9) and temporal lobe neocortex with the superior and middle temporal gyrus (BA21, 22), being a major determining factor in the development of dementia. Thus, cognitive decline in Lewy body dementias is not a consequence of α-synuclein-induced neurodegeneration alone but senile plaque and phosphorylated tau pathology also contribute to the overall deficits.

Keywords: Alzheimer's disease; Lewy body dementia; Parkinson's disease dementia; cognitive decline; dementia with Lewy bodies.

Figure 1

Frequency of pathology scores in (A) control, (B) Parkinson's disease dementia, (C) dementia with Lewy bodies and (D) Alzheimer's disease. The frequency of each pathology score, by brain region, was calculated as described in “Materials and Methods” section. The left‐hand y‐axis represents the percentage of cases with a particular score. BA9, BA21, BA24 and BA40 refer to the Brodmann areas, as defined in Materials and Methods section. “α‐Syn” is α‐synuclein labeling of Lewy bodies and neurites; “tangles” refer to phosphorylated tau labeling of neurofibrillary tangle and neurites; “plaques” is labeling of senile plaques with an antibody to Aβ.