Pre-diseases: forgetfulness, MCI 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 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.” Read more



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