Distinguishing FTD from Alzheimer’s disease using brain imaging

Researchers in Sydney, Australia have been investigating an area deep in the brain called the striatum. Their work suggests that this area and the way it is connected to other areas of the brain could be used as a new marker to help work out whether someone has FTD or Alzheimer’s disease.

We have a number of indicators to look out for on brain scans which suggest when a person has behavioural variant FTD (bvFTD). One previously identified marker which has been found to be useful in diagnosing bvFTD is an area at the front of the brain called the ventromedial prefrontal cortex (VMPFC). If this marker was only ever seen in cases of bvFTD and not in other kinds of dementia, then this would be a conclusive way of making sure that a bvFTD diagnosis was correct. However, this part of the frontal lobe can also be compromised in other dementias such as Alzheimer’s disease. The findings from this latest study by Bertoux and colleagues indicate that there might be another brain marker that can help us to distinguish between bvFTD and Alzheimer’s disease.

The striatum is a region deep in the brain below the cortex. It is characterized by its ‘striped’ effect (‘striatum’ is Latin for striped), created by a line of white matter which separates two areas of grey matter, the caudate and the putamen. A third part of the striatum is called the nucleus accumbens. For this study, the researchers subdivided the striatum not in the traditional way into these three areas, but by which parts of the striatum were connected to particular areas of the frontal lobe. This resulted in three slightly different striatal areas: an area of the striatum connected to the VMPFC and two areas connected to another part of the frontal lobe called the dorsolateral prefrontal cortex (DLPFC), one to the anterior section of the DLPFC and one connected to the posterior section. This way of subdividing the striatum is promising in terms of isolating areas responsible for different functions within the brain, as areas that are connected will typically be involved in the same kinds of cognitive processing. For example, the VMPFC and its connecting striatal areas are thought to be involved in processing reward behaviour, a key aspect of abnormal behaviour in bvFTD leading to changes in appetite such as development of a sweet tooth.

The researchers performed MRI scans in three groups of people: individuals with bvFTD, Alzheimer’s disease and healthy controls. They subsequently correlated the atrophy in the three frontal areas (VMPFC, anterior-DLPFC, and posterior-DLPFC) with the corresponding striatal areas. Compared to people with AD and healthy controls, people with bvFTD showed significantly more atrophy in the VMPFC and anterior-DLPFC striatal connections. However, their posterior-DLPFC atrophy was not significantly correlated with the striatal atrophy, an effect that was observed only in people with AD.

These findings indicate for the first time that only some of the atrophy seen in the striatum in these two dementias is related to the associated atrophy in cortical areas. In other words, certain patterns of frontal-striatal atrophy might be specific to each disease type. The group concluded that atrophy of subcortical regions such as the striatum, and the extent to which its corresponding frontal areas of the brain are damaged, could act as a promising diagnostic biomarker for bvFTD.

Reference

Bertoux M, O’Callaghan C, Flanagan E, Hodges JR, Hornberger M. Fronto-Striatal Atrophy in Behavioral Variant Frontotemporal Dementia and Alzheimer’s Disease. Front Neurol. 2015 Jul 1;6:147.

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