A new study, led by neuroscientists from the University of Cambridge, has identified apathy as an important early sign of dementia. The research finds apathy is distinct from depression, and offers a more accurate longitudinal association with the onset of dementia.
Last year a rigorous study from an expert team of international researchers offered some of the strongest evidence to date affirming the hypothesis that an increasing rate of depression is the one of the first clinical signs of cognitive decline.
However, there is still debate over whether the link between depression and dementia is causal. This new research suggests the debate, and discordant data on the topic, may be underpinned by a blurring of the distinction between apathy and depression in many clinical studies.
“There has been a lot of conflicting research on the association between late-life depression and dementia,” says lead author on the study, Jonathan Tay. “Our study suggests that may partially be due to common clinical depression scales not distinguishing between depression and apathy.”
Apathy and depression are often intertwined, but they are distinct neuropsychiatric conditions. Apathy is distinguished by a reduction in goal-orientated behavior, and motivational impairments. Luca Di Santo, a research nurse at King’s College Hospital, clarified the distinction in a 2019 journal article, suggesting misdiagnosing the two conditions could lead to negative treatment outcomes.
“It is easy to think about apathy as a borderline between laziness and depression,” Di Santo writes, “considering them as a part of the same continuum. It is worthwhile to consider that depression may cause apathy but not all depressed patients are apathetic and not all apathetic patients are depressed.”
To study this particular distinction between apathy and depression, and their relationship with dementia, the researchers looked at two independent cohorts with cerebral small vessel disease (SVD), totaling more than 450 subjects. SVD is a common age-related condition and it’s the leading cause of vascular dementia, so following SVD patients for several years before dementia develops offers a good insight into the earliest pre-clinical signs of cognitive decline.
The compelling results revealed those subjects with higher baseline apathy levels, or increasing levels of apathy over time, were at a significantly higher risk of developing dementia. Interestingly, the results showed no similar correlation between depression and dementia, even when a subject’s rate of depression increased over time.
This implies that apathy is not a risk factor for dementia per se, but rather an early symptom of white matter network damage…
Affirming the hypothesis that apathy is an early sign of cognitive decline, the researchers reference recent MRI studies finding SVD damages specific white matter networks relating to motivation and healthy cognitive functions. This suggests as SVD progresses, an early stage of pre-dementia neurodegeneration can manifest in apathetic behavior.
“This implies that apathy is not a risk factor for dementia per se, but rather an early symptom of white matter network damage,” the researchers write in the study. “Indeed, recent theoretical work proposed that certain symptoms of apathy are synonymous with defined cognitive deficits. If this is the case, then apathy may manifest early as a reduction in attention towards reward stimuli, then later, as an inability to learn or remember rewarding behaviours.”
The follow-up data in the study only spans five years, so more longitudinal data is necessary to better ascertain the link between apathy and dementia. Nevertheless, Tay does point out increasing apathy could be a useful way to identify older adults in the early stages of dementia.
“Continued monitoring of apathy may be used to assess changes in dementia risk and inform diagnosis,” says Tay. “Individuals identified as having high apathy, or increasing apathy over time, could be sent for more detailed clinical examinations, or be recommended for treatment.”
The new study was published in the Journal of Neurology, Neurosurgery, & Psychiatry.
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