Apathy could be an early warning sign of dementia in people with cerebral small vessel disease but depression is not, research suggests.

Cerebral small vessel disease (SVD) is the narrowing of the small blood vessels deep inside the brain.

The research, led by Cambridge University, suggests the belief that depression is a risk factor for dementia may be because some depression scales used by clinicians and researchers partially assess apathy.

The study, published in the Journal of Neurology, Neurosurgery & Psychiatry, is based on analysis over several years of more than 450 SVD patients in the UK and in the Netherlands.

Scientists found that individuals with higher baseline apathy, as well as those with increasing apathy over time, had a greater risk of dementia.

In contrast, neither baseline depression nor change in depression had any detectable influence on dementia risk.

The relationship between apathy and dementia remained after controlling for other well-established risk factors for dementia including age, education, and cognition.

Apathy, defined as a reduction in “goal-directed behaviour”, is a common neuropsychiatric symptom in SVD, and is distinct from depression, which is another symptom in SVD.

SVD may occur in one in three elderly people and is the most common cause of vascular dementia.

Vascular dementia is caused by reduced blood flow to the brain, which damages and eventually kills brain cells.

Lead author Jonathan Tay, from Cambridge’s Department of Clinical Neurosciences, said: “There has been a lot of conflicting research on the association between late-life depression and dementia.

“Our study suggests that may partially be due to common clinical depression scales not distinguishing between depression and apathy.

“Continued monitoring of apathy may be used to assess changes in dementia risk and inform diagnosis.

“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 study’s participants, recruited from three hospitals in south London and Radboud University’s Neurology Department in the Netherlands, were assessed for apathy, depression and dementia over several years.

In the UK cohort, nearly 20% of participants developed dementia, while 11% in the Netherlands cohort did, likely due to the more severe burden of SVD in the UK cohort.

In both datasets, patients who later developed dementia showed higher apathy, but similar levels of depression at baseline, compared with patients who did not.

The study provides the basis for further research, including the mechanisms that link apathy, vascular cognitive impairment, and dementia.

It is the first study to examine the relationships between apathy, depression, and dementia in individuals with SVD, Cambridge University said.