Depression or Dementia? Imaging May Solve Diagnostic Dilemma

Megan Brooks

February 22, 2017

Decreased blood flow in specific regions of the brain, as seen on single-photon emission computed tomography (SPECT), may help differentiate between depression and cognitive disorders, a new study suggests.

"Functional neuroimaging, in this case with perfusion neuroimaging, can identify quantifiable patterns that allow for distinguishing between depression and cognitive disorders such as dementia with high accuracy," study investigator Cyrus A. Raji, MD, PhD, of the University of California, San Francisco, Medical Center, told Medscape Medical News.

"This application is important especially in patients for which symptoms of depression may be confused for dementia and vice versa. Future work will continue to refine this approach with outcomes studies," Dr Raji said.

The study was published online February 15 in the Journal of Alzheimer's Disease.

Diagnostic Dilemma

Cognitive impairment is present in roughly half of individuals with late-onset depression, and depression is seen in 9% to 65% of individuals with dementia, the investigators note. The prevalence of depression in patients with mild cognitive impairment is 25%. Therefore, it can be "challenging to diagnostically disentangle" depression and cognitive disorders (CDs) from one another, they write.

Recent evidence suggests that perfusion SPECT shows findings specific to depression and to CDs. "Thus, it remains a viable choice for separating these two groups of brain disorders. However, studies with SPECT that attempt to distinguish dementia, CDs, and co-morbid cases are lacking," they write.

To investigate, Dr Raji and colleagues studied 4541 older adults with depression and/or cognitive disorders (Alzheimer's disease, vascular dementia, dementia not otherwise specified, and amnestic disorders not otherwise specified). The disorders were determined on the basis of DSM-IV diagnostic critereia. Altogether, 847 participants had CDs, 3269 had depression, and 425 had both depression and a CD.

In general, perfusion was decreased in multiple regions of the brain in individuals with CDs in comparision with individuals with dementia. Those regions included the hippocampus, the amygdala, and the frontal and temporal regions, among others, the researchers report. The group with CDs and depression generally showed a higher magnitude of additive hypoperfusion in these regions compared to those with either diagnosis.

"The accuracy of the linear discriminant probabilities in identifying CDs from depression was 86% with a leave one out cross validated accuracy of 83%. The area under the cure was 86% with sensitivity of 80% and specificity of 75%," they report in their article.

Discriminant analysis distinguished depression and CDs from comorbid cases with correct classification of 90.8% and cross validated accuracy of 88.6%. The area under the curve was 83% with sensitivity of 80% and specificity of 70%, they note.

Distinguishing depression from CDs is a "critical clinical question that has practical implications for patient management and treatment," lead researcher Daniel G. Amen, MD, of Amen Clinics, Costa Mesa, California, said in a statement. "These disorders have very different prognoses and treatments, and being able to improve diagnostic accuracy can improve outcomes for some patients."

Caveats, Cautionary Notes

Commenting on the findings for Medscape Medical News, Davangere Devanand, MBBS, professor of psychiatry and neurology, Columbia University Medical Center, New York City, noted that distinguishing dementia from depression "can be difficult clinically, so the SPECT findings in this study are potentially useful."

Clinically, however, "if someone has dementia, that is usually obvious to the physician, and even the nurse or office assistant who talks to the patient for a couple minutes. So diagnostic imaging is not necessary in most cases; it becomes useful in patients with mild memory loss when the diagnosis is unclear," said Dr Devanand.

"Another point about SPECT is that the blood flow decline increases with progression of dementia. So if they included a large number of patients with moderate to severe dementia, the results are expected," he said.

Dr Devanand also noted that the statistically significant age difference between the depressed group (mean age, 59 years) and the CD group (mean age, 68 years) "may account for the findings, because as we grow older, we have decreased blood flow as a function of age, not necessarily dementia."

He cautioned that the results of this study are based on "complex statistical analyses that are not available to the practicing radiologist/nuclear medicine specialist physician who reads the SPECT scan visually."

The study was sponsored by Amen Clinics, owned by Dr Daniel Amen. Dr Raji has received consulting fees from the Change Your Brain Change Your Life Foundation and Brainreader ApS.

J Alzheimers Dis. Published online February 15, 2017. Abstract

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