Using radiotracers and PET scans to diagnose dementia


These cross-sectional PET scans of the brain using the radiotracer 18F-FDG, depict the patterns in a normal patient (left) and a patient with Alzheimer’s disease respectively. — Dr ALEX KHOO CHEEN HOE

Mental health has been often overlooked in the past, but has now been propelled into the spotlight with the Covid-19 pandemic.

Many people suffer from mental stress due to various conditions, mainly socioeconomic and relationship-related issues.

While these problems can be remedied, there is also an insidious condition that has been sidelined in our society, namely dementia.

This condition frequently presents to doctors with the complaint of “losing my mind”.

In our cultural landscape, dementia (also known colloquially in Bahasa Melayu as “nyanyuk”) has somehow been accepted as a part of the ageing process.

Dementia is the clinical term used to describe a collection of symptoms representing cognitive decline.

These include loss of memory, thinking, comprehension, judgement, orientation and language, which all affects the ability to execute activities of daily living.

Because dementia does not occur overnight, but rather, progressively, many of the signs of cognitive deterioration are overlooked until the condition has significantly progressed.

In fact, depression and paranoia can begin up to 24 and 36 months respectively prior to a diagnosis of dementia.

There are various causes for dementia, with the commonest being Alzheimer’s disease, which accounts for 60-70% of total dementia cases worldwide.

Other causes include vascular dementia (due to stroke), Lewy Body dementia, fronto-temporal dementia, Parkinson’s disease dementia, and dementia due to medical-related conditions such as vitamin B12 insufficiency and hypothyroidism.

It is important to identify which type of dementia is afflicting a particular person as treatment is available for many of these conditions.

While there is no known cure for Alzheimer’s disease at the moment, current medications can slow the progression of the disease.

There are also clinical trials underway to find an effective way to treat it.

Therefore, early detection and evaluation is crucial.

Imaging for dementia

Clinically, it is not easy to distinguish between the various types of dementia.

Thus, doctors frequently have to rely on further investigations such as blood tests, brain imaging and functional brain studies.

If detected early, medically-related conditions such as those due to the side effects of drugs, vitamin deficiencies, thyroid dysfunction and normal-pressure hydrocephalus can be treated.

For Alzheimer’s disease, the only definitive diagnostic method is through a biopsy of brain tissue.

However, this is not routinely done and doctors tend to rely on clinical evaluation and imaging studies.

Functional imaging nuclear medicine studies use various radiotracers such as 18F-Fludeoxyglucose (FDG), 18F-Florbetapir, 18F-Flutemetamol and C-11 Pittsburgh compound B, to differentiate Alzheimer’s disease from other varieties of dementia, as well as to detect the early onset of the disease.

These can be visualised via positron emission tomography (PET) scans.

Roughly half of patients with Parkinson’s disease also suffer from dementia.

Studies have shown that patients with Parkinson’s have about six times higher risk of developing dementia, compared to those without the disease.

It is therefore essential that appropriate treatment be administered to this group of patients, considering that dementia significantly contributes to illness and death.

Some Parkinson’s patients in the early stage of the disease have similar symptoms to patients with essential tremors ‑ a different neurological condition.

In most cases, the differentiation between the two conditions is straightforward, but can be difficult in some cases.

This can be solved with the use of radiotracers such as 123i-Ioflupane (DaTscan), 99m Technetium (Tc-Trodat-1) and 18F-Dopa (Fluorodopa) to distinguish between these groups of patients.

A complaint of “losing one’s mind” should not be something that is taken lightly.

It is worthwhile to investigate the underlying cause as it could be something that can be treated if caught early enough.

With currently-available medical technology, we are in a better position to accurately diagnose and “control” the outcome of such illnesses.

Associate Professor Dr Prem Kumar Chandrasekaran is a consultant neuropsychiatrist and Dr Alex Khoo Cheen Hoe is a consultant nuclear medicine physician. For more information, email starhealth@thestar.com.my. The information provided is for educational and communication purposes only, and should not be considered as medical advice. The Star does not give any warranty on accuracy, completeness, functionality, usefulness or other assurances as to the content appearing in this article. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.

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