Atypical Clinical Manifestations of Cerebral Amyloid Angiopathy

[Current findings on the coincidence of cerebral amyloid angiopathy and Alzheimer's disease]

Die zerebrale Amyloidangiopathie (CAA) tritt trotz verschiedener Pathomechanismen häufig koinzident zur Alzheimer-Demenz auf. Sie moduliert kognitive Defizite im Rahmen der Alzheimer-Erkrankung (AD) annehmbar durch additive Effekte, auch wenn die diesbezüglichen Zusammenhänge komplex sind. Die pathophysiologische Gemeinsamkeit beider Erkrankungen besteht in einem gestörten Amyloidmetabolismus, distinkt ist jedoch die pathologische Prozessierung von Amyloidvorläuferproteinen. Die CAA mit ihren verschiedenen Subtypen ist eine pathomechanistisch heterogene Gefäßerkrankung des Gehirns. Vaskuläre und parenchymatöse Amyloidablagerungen kommen gemeinsam, aber auch isoliert und unabhängig voneinander vor. Um den spezifischen Beitrag der CAA zu kognitiven Defiziten im Rahmen der AD zu untersuchen, bedarf es daher geeigneter diagnostischer Methoden, die der Komplexität der histopathologischen bzw. bildmorphologischen Charakteristika der CAA gerecht werden, sowie differenzierender testpsychometrischer Verfahren, anhand derer der Beitrag der CAA zu kognitiven Defiziten deskriptiv erfasst und damit ätiologisch besser zuordenbar wird.

MRI and flortaucipir relationships in Alzheimer's phenotypes are heterogeneous

OBJECTIVE

To assess the relationships between MRI volumetry and [18 F]flortaucipir PET of typical and atypical clinical phenotypes of Alzheimer's disease, by genarian (age by decade).

METHODS

Five-hundred and sixty-four participants including those with typical (n = 86) or atypical (n = 80) Alzheimer's dementia and normal controls (n = 398) underwent apolipoprotein E genotyping, MRI, flortaucipir, and 11 C-PiB; all 166 Alzheimer's participants were beta-amyloid positive and all controls were beta-amyloid negative. Grey matter volume and flortaucipir standard uptake value ratios were calculated for hippocampus, entorhinal cortex, and neocortex. Ratios of hippocampal-to-neocortical and entorhinal-to-neocortical volume and flortaucipir uptake were also calculated. Linear regression models assessed relationships among regional volume, flortaucipir uptake, and ratios and phenotypes, within three genarians (50-59, 60-69, and 70+). Voxel-level analyses were also performed.

RESULTS

For 50-59 greater medial temporal atrophy and flortaucipir uptake was observed in the typical compared with atypical phenotype. The typical phenotype also showed greater frontal neocortex uptake with the voxel-level analysis. For 60-69 and 70+ there was greater hippocampal volume loss in the typical compared with atypical phenotype while only the 60-69, but not the 70+ group, showed a difference in hippocampal flortaucipir uptake. We also observed a pattern for higher neocortical flortaucipir uptake to correlate with younger age decade for both phenotypes.

INTERPRETATION

MRI volumetry versus flortaucipir PET relationships differ across Alzheimer's clinical phenotypes, and also within phenotype across age decades. This suggests that there is potential risk of masked effects by not accounting for genarian in participants with beta-amyloid and tau-positive biomarker defined Alzheimer's disease.