New nuclear imaging techniques help in detecting Alzheimer's disease much earlier than before. Recently developed tracers, used with positron emission tomography (PET) make beta-amyloid in the brain visible. This part of a protein, which is a main causal factor of Alzheimer's, can now be detected long before the onset of the symptoms. "This helps doctors to confirm their diagnosis and to plan the individually appropriate treatment strategy right from the start. Also, it will allow to apply future medications, which are currently being developed, in time," says Professor Swen Hesse, expert of the European Association of Nuclear Medicine (EANM).
Alzheimer's disease is the most frequent cause of dementia, a decline in mental ability that usually develops and progresses slowly. Memory and judgment are impaired, and personality may deteriorate. It affects mainly those aged over 60 and is one of the most important causes of disability in the elderly. The number of Europeans suffering from this dementia is estimated to double by 2040. Alzheimer's is a large burden for the patients and their families as well as for the health-care systems, due to the high socio-economic costs. Hence, improving diagnosis and treatment belong to the top priorities on the European Union's health-care agenda. Although there is no cure so far, certain medications can reduce the symptoms and thus preserve the patients' mental abilities to a certain degree for a limited time span. The earlier treatment is being started, the higher its efficacy. The fact that novel and more lasting therapies might become available soon, increases the importance of early diagnosis.
Detecting brain-destroying plaques
The target of the PET examination is beta-amyloid, which is the chief component of plaques that harm the brain's neurons and are one of the hallmarks of Alzheimer's. Three different tracers (radioactively labelled substances the patient is injected with) have been developed recently, which make these plaques visible on the computer screen. One of the substances (florbetapir F-18) has already been approved by the health-care authorities of the European Union and the USA alike, while the two other ones (flutemetamol F-18 and florbetaben F-18) are expected to be approved by both authorities before long. With the help of these tracers, the likelihood of Alzheimer's disease can be detected up to fifteen years before the onset of severe mental impairment. However, while a negative PET scan - one that shows little or no beta-amyloid accumulation in the brain - excludes Alzheimer's as the cause of the patient's disease, this does not quite work the other way round since other forms of dementia such as dementia with Lewy bodies (DLB) can have positive scans, too, and a positive scan does not necessarily mean clinically frank dementia. On-going studies will show whether the use of radioactive amyloid tracers and PET can predict the individual risk of future conversion to Alzheimer's dementia and whether they are suited to assess how patients respond to treatment. For the time being, the nuclear imaging methods are not a replacement but a valuable addition to established diagnostic tools.
Novel tracers will advance treatment
"Amyloid imaging allows doctors to determine right from the start and with high accuracy whether, in patients with mild symptoms, Alzheimer's can be excluded, so that some other kind of dementia or another condition has to be taken into account," says Prof. Swen Hesse. "The effectiveness of these substances was established in excellent clinical studies that showed their accuracy in detecting beta-amyloid in the brain according to histopathological results." According to the EANM, amyloid imaging will advance treatment options by helping to select study participants into clinical trials, which may lead to disease-modifying medications. Such tracers are also prone to new combinations of PET with magnetic resonance imaging (MRI) as stand-alone examinations, being, in fact, two devices in one. This will further reduce scanning time and increase patient's comfort.