It might sound obvious, but for doctors to provide patients with the best possible care, they must be able to diagnose them with the right disease first. That task can be surprisingly difficult for disorders of the brain, which often lack concrete physiological diagnostics.
What’s more, many cognitive and psychiatric disorders have overlapping symptoms or even present together, making it hard for physicians to distinguish among various conditions. For example, depression in the elderly can include cognitive dysfunction such as memory loss, and depressive symptoms are common in patients with dementia.
Depression is also considered a major risk factor for dementia, and an estimated 25 percent of patients have both disorders. However, the root biological causes of the two conditions – and thus their courses of treatment – are very different, so it is essential to diagnose the correct primary affliction.
New Analytical Approach Using Neuroimaging
To help better diagnose patients, a multi-institutional collaboration between UC San Francisco, UCLA, and Thomas Jefferson University applied a new analytic approach to distinguish between depression and dementia using neuroimaging. The scientists used a nuclear imaging technique called single photon emission computed tomography (SPECT) to track blood flow in the brain. Measuring blood flow can identify changes in brain function with great sensitivity, helping scientists to detect the earliest signs of abnormality caused by disease.
By applying machine learning techniques to more than 4,500 functional neuroimaging scans from patients who had been diagnosed with depression, cognitive disorders such as dementia, or both, the researchers identified distinct neuroimaging profiles for each condition. Using these profiles, they distinguished between the disorders with 86 percent accuracy.
In general, patients with dementia had lower blood flow overall than those with depression, and people diagnosed with both depression and dementia had lower blood flow than either condition individually. There were also differences between patient groups in specific regions, which helped characterize each disorder. For example, the hippocampus received less blood in patients with dementia than in those with depression.
Abnormalities in Hippocampus May Serve as Link
Differences in the hippocampus are notable because it is an important memory center in the brain, and it is the first area affected by Alzheimer’s disease. The hippocampus is also an integral part of emotional pathways in the brain and has been connected to depression. However, studies suggest that changes in the region stemming from depression can be reversed by treatment. Abnormalities in the hippocampus may serve as the link between the two conditions.
Interestingly, there was no difference in the severity of depression symptoms between patients with depression and those who had both depression and dementia. However, the scientists did detect differences in blood flow between these two groups, correctly predicting a dual diagnosis 83 percent of the time.
The study findings were reported in the Journal of Alzheimer’s Disease.
“The real value of the study, in my opinion, is not necessarily distinguishing between people with only depression or only dementia, but in identifying persons who have both conditions,” said Cyrus Raji, MD, PhD, a UCSF clinical fellow in the Department of Radiology and Biomedical Imaging and co-author on the study. “Those are complex cases because you have overlapping symptoms between the two disorders. Being able to correctly diagnose the source of cognitive problems is helpful in guiding optimal treatment.”
