Diagnosis of Alzheimer's disease

There are as yet no identified biological markers for Alzheimer's disease that have been proved to be reliable and accurate indicators. Currently a diagnosis is made based upon clinical observations and testing of cognitive capacity and memory loss.

Additional testing and clinical assessment is also required to rule out other conditions that have similar symptoms such as depression. As the diagnosis has to be based upon observable characteristics, it can only be diagnosed once the condition has progressed and considerable neurological damage has already occurred.

Historically a confirmed diagnosis of Alzheimer's disease (AD) could only be achieved through post mortem identification of the neurofibrillary tangles and / or abnormal plaque deposits on the brain known to be associated with AD.

Recent research is indicating that various brain scanning techniques and genetic testing can also be used to identify the likelihood of Alzheimer's disease. The latest research is indicating that the existence of plaque deposits alone are not a sufficiently accurate indicator of AD as plaque build-up occurs in a significant proportion of the population and not all people who develop plaques develop AD. Identifying plaque deposits will probably need to be used in conjunction with other bio markers to ensure accurate diagnosis of Alzheimer's disease.

• Scanning technology such as magnetic resonance imaging (MRI), computed tomography (CT) and positron emission tomography (PET) can reveal atrophy of the brain and are being studied as to their efficacy in identifying evidence of amyloid plaque build up and the relationship of this build up to the progression of Alzheimer's Disease.
• Genetic testing is another area being studied. Though this is unlikely to become a means of diagnosis on its own, current evidence indicates it has potential as an early indicator of risk and can improve the accuracy of a diagnosis using other bio markers such as beta amyloid.
• Differential diagnosis and assessment by a specialist is important, in particular for distinguishing Alzheimer's disease from "normal" memory and cognitive impairment of ageing, and from other types of dementia and other disorders such as delirium and major depression.

There is some evidence to indicate that, certainly in the past, GPs are cautious about making a diagnosis of Alzheimer's disease. A survey of 281 GPs in the UK found that only 39% would inform their patients of a diagnosis of dementia, compared to 95% who would inform them of a diagnosis of terminal cancer¹. Reasons for not telling include:

• emotional distress and other negative impacts for the person and their family,
• fear of incorrect diagnosis,
• a judgment that there is no benefit in the person knowing, or
• a request from the family or carer not to tell.

There is no evidence however that informing the person is detrimental. On the contrary, information may assist future planning and the development of strategies for managing the illness and associated disability. It would also facilitate access to services including medical treatments and community services, and assist families, carers and others to understand what is happening.

1. Black et al, (2001) Diagnosing Dementia: a reference paper, Alzheimer's Australia, September 2001