Like with any neurodegenerative disorder, treating Alzheimer’s early is key to arresting the disease’s inevitable mental decline. But this is easier said than done. The earliest stages of Alzheimer’s disease — before the symptoms of dementia become apparent — are vague and undefined, and neuroscientists remain divided about how best to characterize the distinct clinical phases of disease progression.
In April, a working group formed by the US National Institute on Aging and the Alzheimer’s Association (NIA-AA) revised the disease’s diagnostic criteria for the first time in 27 years to reflect latest findings about the asymptomatic phases of Alzheimer’s. The group divided cognitively normal people into three stages based on presence of biomarkers in their blood or spinal fluid: a ‘pre-clinical’ phase in which early biomarkers such as beta-amyloid show up but without neurological changes; a second stage showing shrinkage or reduced metabolic activity of neurons and a final stage with gradual cognitive decline, like subtle memory loss.
The diagnostic guidelines were intentionally left vague to allow for updates in the face of emerging data. And less than six months after the criteria came out, a new report has found this trio of stages lacking.
In the study, a team led by Mayo Clinic radiologist Clifford Jack, who was also on the NIA-AA panel, used PET imaging on 450 cognitively normal elderly people aged 70 and up and attempted to apply the NIA-AA criteria. Reporting in the Annals of Neurology, the researchers found that only a third of these subjects fit into the three stages defined by the working group. The rest, they recommended, should be assigned to two additional groups: one for people who show no abnormal biomarkers or clinical symptoms whatsoever, and another for people who develop dementia for reasons other than Alzheimer’s Disease, such as cerebral vascular disease, mini-strokes or Lewy Body disease.
Together, these studies are the first attempts to systematically characterize early Alzheimer’s pathology and use this definition to classify elderly subjects. A commentary in Nature Medicine last month pointed out the importance of treating Alzheimer’s disease early; these guidelines are a definite step towards that goal.
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