Etiology and progression of Alzheimer’s disease has remained a mystery. Imaging through PET scans has allowed researchers and clinicians to monitor toxic tau protein accumulates in the brain. Dr. Oskar Hansson, professor of neurology at Lund University led and supervised research.
The study includes a variety of participants: without symptoms “pre-symptomatic Alzheimer’s”, mild memory difficulties and those with fully developed Alzheimer’s dementia. Sample size included 1,612 individuals and length of the study was two years. By comparing PET scans of all groups, researchers identified four clear patterns of tau pathology. Not one pattern dominates and each pattern has a certain symptomatic presentation:
- Variant one: tau spreads mainly within the temporal lobe and primarily affects memory. Variant one occurred in 33 percent of all cases.
- Variant two: In contrast to variant one, this variant spreads in the rest of the cerebral cortex. The individual has less memory problems than in the first variant, but on the other hand has greater difficulties with executive functions, that is, the ability to plan and per-form an action. Variant two occurred in 18 percent of all cases.
- Variant three: The accumulation of tau takes place in the visual cortex, i.e. in the part of the cerebrum where information from the optic nerve is processed and classified. The visuospatial processing of sensory impressions in the brain is affected in individuals with this pattern. They have difficulty orienting themselves, distinguishing shapes and contours, distance, movement and the location of objects in relation to other objects. Variant three occurred in 30 percent of all cases.
- Variant four: Tau spreads asymmetrically in the left hemisphere and primarily affects the individual’s language ability. Variant four occurred in 19 percent of all cases.
Knowledge of etiology is the first step with identifying proper treatment. More longitdunal studies will show how each pattern progresses. With more information, researchers may learn how to stop or prevent progression.