Deterioration of Brain’s Reward Circuitry Is a Unique Trait of Early-Onset Dementia, Study Shows

Because Alzheimer’s and other forms of dementia occur most often in elderly people, it’s common for younger people to be misdiagnosed with something else, such as depression, when they actually have a form of early-onset dementia, such as frontotemporal dementia (FTD), which most commonly affects those under the age of 60.

Depression and frontotemporal dementia have many overlapping symptoms, so it’s not surprising that doctors are more likely to diagnose patients with the former over the latter. Both can present with a loss of enthusiasm, empathy, or motivation and a sense of lethargy. It’s an understandable mistake, especially because doctors come across cases of depression on a regular basis, whereas they likely see FTD less often in their practices.

However, it is important for patients to get the appropriate diagnosis when they have FTD so that they can get the appropriate treatment to keep their quality of life as high as possible for as long as possible.

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It is critical, therefore, to find a symptom of FTD that is entirely distinct from the symptoms of adult depression so that doctors can differentiate between the two diseases in their patients. Now, thankfully, researchers believe they may have found just the thing.

Muireann Irish and her team at the University of Syndey have identified a particular symptom of FTD that seems to be unique to it and therefore can differentiate it from clinical depression. The symptom, known as anhedonia, is described as the inability to enjoy pleasant experiences.

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For their study, the researchers used cognitive, behavioral, and neuroimaging assessments to analyze Alzheimer’s or dementia patients and healthy control patients. Behavioral tests revealed that anhedonia was highly prevalent in patients with FTD but less so in other forms of dementia. FTD patients who had anhedonia experienced a distinct lack of interest in rewarding experiences and enjoyable hobbies, such as eating their favorite meal or spending time with a friend.

The researchers took MRI images of their patients and conducted a voxel-based morphometry analysis to examine changes in grey matter signal intensities in the brain. They were able to clearly see in those images that the neural circuitry patterns that accompany anhedonia differ from those involved in apathy or depression. The changes in a brain with anhedonia are also different from the degeneration that commonly occurs in Alzheimer’s disease.

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FTD patients with anhedonia show most of their neurological deterioration in the frontostriatal grey matter network, which is responsible for the experience of pleasure.

“We are very excited by these findings as they reveal a symptom that has not previously been documented in frontotemporal dementia, as well as the neural bases of this symptom, opening the door to potential treatments,” says Irish.

More research is needed to fully understand what causes anhedonia and how it affects a patient with FTD, but researchers know this unique symptom has to do with a deterioration of the reward circuitry in the brain. A simple MRI can determine whether a person’s failure to enjoy a pleasant experience is due to that deterioration (which points to anhedonia and FTD) or another neurological abnormality (which may point to depression or another condition).

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“Our findings are also important for understanding the subjective experience of the person living with dementia, for the delivery of personalized care, as well as revealing broader insights into a fundamental aspect of the human condition,” says Irish. “If we pause to consider what it might be like to lose our capacity to experience pleasure, we can appreciate the immense need for future work in this field to restore some of the simple pleasures in life to those affected by these cruel disorders.”

The team’s research was published in the Oxford academic journal Brain. Future research will need to focus on the relationship between the deterioration of the reward circuitry in the brain and the appearance of anhedonia in a patient’s life.

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