New Alzheimer Diagnostic Criteria: Moving Forward, Looking Back

Revised diagnostic criteria for Alzheimer's disease, endorsed by the National Institute on Aging and the Alzheimer's Association, were published in the May 2011 issue of Alzheimer's and Dementia: The Journal of the Alzheimer's Association. The three articles and an introduction that lay out the criteria can now be accessed at http://www.alz.org/research/diagnostic_criteria/. Drafts of the revised criteria for Alzheimer's disease (AD) were initially released for discussion and review at the Alzheimer's Association International Conference on Alzheimer's Disease in July 2010. That first release was accompanied by much media attention and a fair bit of public critique, especially from those outside the Alzheimer research community. Like the old criteria, the new ones are aimed primarily at researchers, to help improve the characterization of research volunteers and set a scientific framework for defining the key elements of the disease process. Nonetheless, just like their predecessors, they are sure to cross over into clinical practice.

The revised criteria represent the first major update since 1984. Knowledge gained in the interval between the old criteria and the new ones has fundamentally changed our understanding of the processes that lead to AD. In the epoch since those revered 1984 "McKhann criteria" were adopted, the details of the structure and metabolism of β-amyloid, the role of tau protein in neurofibrillary tangles, modern imaging techniques like MRI and PET, and the concept of mild cognitive impairment have all been characterized. The time was certainly ripe for something new, and these breakthroughs are all included in the update criteria.

Perhaps the most important conceptual change in the criteria is a journey even further into the past, beyond 1984, to a time when the lexicon more clearly separated the clinical state of dementia from the pathological process of Alzheimer's disease. Before the new criteria, the pre-1984 terminology "Dementia of the Alzheimer type," was - if not extinct - certainly close to the brink.

Echoing the old way of thinking, the new criteria lay out broad three phases of AD, 1) Dementia due to AD, 2) Mild Cognitive Impairment due to AD, and 3) Preclinical stages of AD. The role of biomarkers to identify underlying AD pathophysiology increases in importance for the more mild MCI and preclinical phases. It was the dependence on biomarker technologies (and their cost), that drummed up much of the controversy when the criteria were first released. Pundits have argued that insiders are simply creating new disease states so Big Business can make even more money for itself through expensive tests for untreatable or clinically irrelevant conditions. It is true that commercial interests will certainly benefit from an expanded market for early AD diagnosis; the immense costs of an expanding AD population (diagnosed early or not) are truly frightful no matter how you look at them. However, in light of the fundamental changes in our understanding Alzheimer's disease since 1984, the critics seem unduly nihilistic in implying that we should continue to conceptualize AD with the methods of the last century.

For additional commentary, I can recommend the following article by Kenneth Covinsky, a professor at UC-San Francisco. http://www.kevinmd.com/blog/2011/01/alzheimers-disease-diagnosis-criteria-critical-review.html