However, additional cognitive and behavioral symptoms vary between patients with a clinical and pathological diagnosis of Alzheimer's disease.
A key area of research is focused on understanding factors that contribute to symptom variability in Alzheimer's disease.
A team of researchers from Singapore and Harvard Medical School recently published an important study on this topic.
They analyzed structural MRI images from a group of 188 subjects in the Alzheimer's Disease Neuroimaging Initiative.
Using a mathematical model known as latent Dirichlet allocation they were able to identify three distinct areas of atrophy of variable severity in their cohort. These three factors were found to be:
- Temporal atrophy: temporal cortex, hippocampus and amygdala
- Cortical atrophy: frontal, parietal, lateral temporal and lateral occipital cortex regions
- Subcortical atrophy: striatum, thalamus and cerebellum
Individual patterns of atrophy within subjects were found to be stable over time. This means the atrophy patterns are not just a reflection of the stage of the Alzheimer's disease.
As expected, patterns of atrophy correlated with neuropsychological domains of impairment. Temporal atrophy subjects had the greatest memory impairment. Cortical atrophy patients showed the most impairment in executive function. Subcortical atrophy subjects had lower levels of executive function and memory impairment and showed a slower rate of cognitive decline.
Patients tended to fall into factor groups where more than one area of atrophy was noted, i.e. cortical and temporal atrophy but not subcortical atrophy.
The authors note their findings support the heterogeneity of Alzheimer's disease affecting different cognitive and behavioral features as well as variability in disease progression.
This is an important study in understanding the clinical manifestation of Alzheimer's disease. Readers with more interest in this research can access the free full-text manuscript by clicking on the link in the citation below.
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Brain image highlighting regions of the subcortex is an iPad screen shot from the app Brain Tutor.
Zhang X, Mormino EC, Sun N, Sperling RA, Sabuncu MR, Yeo BT, & Alzheimer’s Disease Neuroimaging Initiative. (2016). Bayesian model reveals latent atrophy factors with dissociable cognitive trajectories in Alzheimer's disease. Proceedings of the National Academy of Sciences of the United States of America PMID: 27702899
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