In a study of 4,541 people, researchers used single-photon emission computed tomography (SPECT) imaging to distinguish between those who had dementia, those who had depression, and those suffering from both conditions. By measuring blood flow to different regions of the brain, the researchers found that SPECT could distinguish depression from cognitive disorders with 83 percent accuracy. The paper, published in the Journal of Alzheimer’s Disease,was the largest study of its kind ever conducted.
Correctly identifying what is wrong with a patient is obviously the first step towards proper treatment. But depression and cognitive disorders are both common, they share many of the same symptoms, and they can appear simultaneously. While studies indicate that about a quarter of people who have cognitive disorders have depression, “it is often challenging to diagnostically disentangle depression and cognitive disorders from one another,” the authors wrote. Of the 4,541 people studied, 847 were diagnosed with cognitive disorders, 3,269 with depression, and 425 with both. The researchers defined “cognitive disorders” as Alzheimer’s disease, vascular dementia, and dementia or amnestic disorders otherwise unspecified.
Traditionally, clinicians use checklists and rating sheets to diagnose patients with these disorders. “My thought is that that’s not good enough,” said Daniel Amen, a psychiatrist and founder of the Amen Clinic in Costa Mesa, CA, and the lead author of the study. When scans are ordered to aid in diagnosis, magnetic resonance imaging (MRI), rather than SPECT, are common. MRIs often “miss things that are potentially treatable, like depression,” said Amen. “The functional imaging will give you a differential diagnosis that is actionable. That’s exciting!”
SPECT is not a new technology. The machines, which use a radioactive tracer to examine blood flow, have been in widespread use since the 1980s. This type of nuclear imaging is commonly used in heart and lung diagnostics. “The technology is here. It’s available. There are literally thousands of studies,” said Amen. “[SPECT] is a mature technology, yet it’s dramatically underutilized.”
Using SPECT, the researchers found that people with dementia had lower overall blood flow in the brain than those with depression. The people diagnosed with both depression and dementia had lower blood flow than either condition alone. The areas of the brain with reduced blood flow also differed depending on the diagnosis. People with cognitive disorders showed reduced flow in the hippocampus as well as the temporal and parietal lobes. SPECT was able to distinguish depression from cognitive disorders with 86 percent accuracy, and was able to distinguish co-morbid cases—people who had both depression and a cognitive disorder—with 83 percent accuracy.
“The technology is already there. The research is already there,” said Amen. “The limiting factor is educating clinicians--Both the people who read the scans and the people who would order the scans.”
George Perry, editor-in-chief of the Journal of Alzheimer's Disease, said cost may also help explain why the use of SPECT imaging isn’t more ubiquitous. “They’re less expensive than PET scans, but they’re more expensive than other things,” said Perry, who is also dean of the College of Sciences at the University of Texas at San Antonio. He added that if there’s a chance—even if it’s relatively remote—that a patient’s needs could be addressed, then “the scan is worth it.”
Read this on the Bioengineering Today website