Brain Imaging Accurately Distinguishes Diverse Patterns Of Dementia

Dementia with Lewy bodies (DLB) is the second most frequent cause of degenerative dementia in elderly people after Alzheimer's disease.

Dementia with Lewy bodies (DLB) is a relatively newcomer under the umbrella term – dementia (cognitive decline). Often confused between Alzheimer's disease and Parkinson-related dementia (PDD), DLB is the second most frequent cause of degenerative dementia in elderly people (15 to 25% of cases at autopsy)" after Alzheimer’s disease, as per a study published in the Journal of Neurology, Neurosurgery and Psychiatry (a publication of the British Medical Journal group).

As DLB includes symptoms in common with Alzheimer's disease (AD) and Parkinson's disease (PD), it requires careful inspection by the clinicians.

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‘Often confused between Alzheimer's disease and Parkinson-related dementia (PDD), DLB – Dementia with Lewy bodies is the second most frequent cause of degenerative dementia in elderly people (15 to 25% of cases at autopsy)" after AD. A combination of imaging technique called SPECT with intravenous injection of a radioactive compound, [123I] FP-CIT, allows the clinicians to differentiate DLB not only from AD but also from Parkinson's disease.’

Alzheimer's disease (AD) is a neurodegenerative disease that leads to gradual memory loss and behavioral changes. It is characterized by the formation of beta-amyloid plaques and the tau proteins in the brain tissues.

Whereas, in Parkinson's disease (PD), a progressive neurodegenerative disorder that primarily affects movement, there is a loss of nerve cells – neurons that produce a chemical messenger (neurotransmitter) in the brain called dopamine (black substance).

PD is characterized by the formation of inclusion proteins called alpha-synuclein in the form of Lewy bodies. Symptoms include gradual onset of mild tremors in one hand at rest followed by walking and balancing difficulty, memory deterioration, and carrying out other daily activities.

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Unlike these two conditions, DLB also entails prominent mood and cognitive swings, sleep disorders, and vivid, sometimes terrifying, visual hallucinations.

Generally, these Lewy bodies are limited in their distribution. However, in DLB, the Lewy bodies are diffused widely throughout the brain, as seen in the post mortem reports of Robin Williams, an American actor who was diagnosed with Parkinson's disease at the time of his suicide in 2014. Although a PD diagnosis was made, he and his wife were certain that something else was very wrong with him.

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It is now thought that his suicide was driven by the terrifying hallucinatory experiences that he had suffered for years - and about which he never told anyone, not even his wife. This tragic story was recounted by Susan Schneider Williams in an editorial published in the journal Neurology, in 2016, under the title "The terrorist inside my husband's brain".

SPECT in Dementia with Lewy Bodies

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The study team used an imaging technique called SPECT (single-photon emission computed tomography), which allows distinguishing DLB from Alzheimer's disease, by combining the use of intravenous injection of a radioactive compound, [123I]FP-CIT. This radioactive compound specifically binds to dopamine transporters located in a specific part of the brain called the striatum.

Since the striatal dopamine-producing neurons are depleted in dementia with Lewy bodies (just as they are in Parkinson's disease), but not in Alzheimer's disease, it demonstrates the distinction of DLB from AD.

The present study had been in the making for more than twenty years. "The imaging data was acquired around 1996-1999. These patients were followed from the time of their initial clinical diagnosis (and image collection) to that of their death - in some cases, for about 20 years. We did not have all the data then. Now we do", says Francisco Oliveira, who works in Durval Costa's Lab and is the first author of the paper.

The study also enabled the autopsies to confirm the imaging data with very high accuracy for the first time, that not only differentiates DLB from AD, but also from Parkinson's disease (whose corresponding [123I] FP-CIT distribution patterns are also different from one another).

"To be able to quantitatively make these distinctions between diseases is crucial. These diseases may present overlapping symptoms, which makes the clinical diagnosis difficult in some cases and gives rise to a considerable percentage of misdiagnoses. Studies have shown that, frequently, patients with DLB are clinically diagnosed with AD. Our findings may have a significant impact both on patients and caregivers. In addition, the selection of patients for clinical trials can now be done with more accurate biomarkers", says Francisco Oliveira

Source-Medindia