2 September 2012, 6.23am AEST
The perils of pre-diseases: forgetfulness, mild cognitive impairment and pre-dementia
OVER-DIAGNOSIS EPIDEMIC – David Le Couteur discusses recent changes in the definition of dementia and their ramifications. The pattern of over-diagnosis is the same for many diseases: we screen healthy people and those with minimal symptoms; we use sophisticated technologies that detect early or minor…
OVER-DIAGNOSIS EPIDEMIC – David Le Couteur discusses recent changes in the definition of dementia and their ramifications.
The pattern of over-diagnosis is the same for many diseases: we screen healthy people and those with minimal symptoms; we use sophisticated technologies that detect early or minor abnormalities that may not progress; and we treat people with these abnormalities on the assumption that this will prevent significant illness and death.
The downside of all this medical intervention is that we’re exposing healthy people to the potential harms of diagnosis, investigation and treatment without any certainty about long-term benefits. Indeed, there’s a growing unease that this trend is being driven by the financial benefits of creating a larger market for drugs rather than genuine health gains.
I work in geriatric medicine and over the last few years, I have seen how the changing definitions of dementia and Alzheimer’s disease has insidiously been leading to over-diagnoses.
Screening the healthy
Let’s start with the schema of over-diagnosis: are we screening healthy people and those with minimal symptoms? Yes. In the past, we diagnosed older people complaining of minor memory impairment with “benign senescent forgetfulness”, and told them that it didn’t require any further action. It was, after all, benign.
But this terminology progressed to “mild cognitive impairment (MCI)” and now (more ominously), to pre-dementia and pre-clinical Alzheimer’s disease. We are also being encouraged to screen older people for any memory impairment because this has now been defined as a pre-disease or early disease.
The screening tools are usually simple questionnaires, such as the mini-mental state examination (MMSE). There’s variability in how well the assessments are performed, and forgetting the date or stumbling on a repetition task can lead to a diagnosis of mild cognitive impairment. But how many of these people actually progress to dementia?
Most studies show that only one in ten cases of mild cognitive impairment progress to dementia each year, and many improve. One study that followed outcomes for ten years concluded – “The majority of subjects with MCI do not progress to dementia at the long term.”
Yet all of these people will potentially be faced with the stigma of a dementia diagnosis and its consequences – paternalism, incapacity and loss of autonomy. And then there’s the fear of impending dementia, which can generate stress and despair.
Are we using sophisticated technologies to detect early or minor abnormalities? Yes. In attempt to improve the diagnosis of early dementia, we now have a range of investigations to detect the earliest cases before symptoms have developed. These include brain scans and measurement of biomarkers in the fluid that surrounds the brain.
The gold standard for such diagnoses is post-mortem brain pathology. Alzheimer’s disease is characterised by deposits of a protein called amyloid in plaques between brain cells and another protein called tau in tangles within the cells. But the relationship between amyloid plaques and the clinical features of dementia lessens as people age.
Many older people with the characteristic pathology of Alzheimer’s disease didn’t have any features of dementia at post mortem or memory problems when they were alive. On the other hand, the majority older people with dementia have multiple changes in their brains including those related to ageing and vascular disease. So the characteristic pathology of Alzheimer’s disease is not very useful in diagnosing dementia in the largest group of people with dementia, the elderly.
Are we treating these early abnormalities on the assumption that this will prevent the development of dementia? Yes, in some cases.
There are two groups of medicines available for the symptomatic treatment of Alzheimer’s disease (cholinesterase inhibitors and memantine). Although these drugs have not been proven to have any effect on influencing the progress of dementia, review articles in some medical journals promote the possibility of their “disease-modifying activity” and the need for early treatment with these medicines.
And it’s important to add that a trial of one of these medicines attempting to show a reduction in the conversion from mild cognitive impairment to dementia found that it actually increased the death rate.
The medicines are only funded by the Pharmaceutical Benefits Scheme (PBS) for moderately severe Alzheimer’s disease but undoubtedly some people will be using them (and probably a variety of alternative therapies as well) in the hope that they will delay dementia.
And there are other industries aiming to profit from the diagnosis of mild cognitive impairment (or early and pre-clinical dementia) by selling various brain fitness technologies ranging from video games to mobile phone apps.
Dementia is a tragic illness that places enormous burden and demands on patients, families and society. There’s no question of the value of increasing recognition of the care needs of people living with dementia, and for more research funding. These are essential because effective treatment and prevention of dementia will have a dramatic impact on the human race. But the growing emphasis on early diagnosis of dementia, mild cognitive impairment and preclinical dementia in everyday practice (with the subsequent risk of over-diagnosis and its consequences) seems to be giving the disease, not the patient, greater priority and importance.