A work group convened by the Alzheimer’s Association has released revised biology-based criteria for the diagnosis and staging of Alzheimer’s disease (AD), including a new biomarker classification system that incorporates fluid and imaging biomarkers as well as an updated disease staging system.
“Plasma markers are here now, and it’s very important to incorporate them into the criteria for diagnosis,” senior author Maria C. Carrillo, PhD, Alzheimer’s Association chief science officer and medical affairs lead, told Medscape Medical News.
The revised criteria are the first updates since 2018.
“Defining diseases biologically, rather than based on syndromic presentation, has long been standard in many areas of medicine — including cancer, heart disease and diabetes — and is becoming a unifying concept common to all neurodegenerative diseases,” lead author Clifford Jack, Jr, MD, with Mayo Clinic, Rochester, Minnesota, said in a news release from the Alzheimer’s Association.
“These updates to the diagnostic criteria are needed now because we know more about the underlying biology of Alzheimer’s and we are able to measure those changes,” Jack added.
The 2024 revised criteria for diagnosis and staging of AD were published online on June 28 in Alzheimer’s & Dementia.
Core Biomarkers Defined
The revised criteria define AD as a biologic process that begins with the appearance of AD neuropathologic change (ADNPC) in the absence of symptoms. Progression of the neuropathologic burden leads to the later appearance and progression of clinical symptoms.
The work group organized AD biomarkers into three broad categories: (1) core biomarkers of ADNPC, (2) nonspecific biomarkers that are important in AD but are also involved in other brain diseases, and (3) biomarkers of diseases or conditions that commonly coexist with AD.
Core Alzheimer’s biomarkers are subdivided into Core 1 and Core 2.
Core 1 biomarkers become abnormal early in the disease course and directly measure either amyloid plaques or phosphorylated tau (p-tau). They include amyloid PET; cerebrospinal fluid (CSF) amyloid beta 42/40 ratio, CSF p-tau181/amyloid beta 42 ratio, and CSF total (t)-tau/amyloid beta 42 ratio; and “accurate” plasma biomarkers, such as p-tau217.
“An abnormal Core 1 biomarker result is sufficient to establish a diagnosis of AD and to inform clinical decision making [sic] throughout the disease continuum,” the work group wrote.
Core 2 biomarkers become abnormal later in the disease process and are more closely linked with the onset of symptoms. Core 2 biomarkers include tau PET and certain soluble tau fragments associated with tau proteinopathy (eg, MTBR-tau243) but also pT205 and nonphosphorylated mid-region tau fragments.
Core 2 biomarkers, when combined with Core 1, may be used to stage biologic disease severity; abnormal Core 2 biomarkers “increase confidence that AD is contributing to symptoms,” the work group noted.
The revised criteria give clinicians “the flexibility to use plasma or PET scans or CSF,” Carrillo told Medscape Medical News. “They will have several tools that they can choose from and offer this variety of tools to their patients. We need different tools for different individuals. There will be differences in coverage and access to these diagnostics.”
The revised criteria also include an integrated biologic and clinical staging scheme that acknowledges the fact that common co-pathologies, cognitive reserve, and resistance may modify relationships between clinical and biologic AD stages.
Formal Guidelines to Come
The work group noted that currently, the clinical use of AD biomarkers is intended for the evaluation of symptomatic patients, not cognitively unimpaired individuals.
Disease-targeted therapies have not yet been approved for cognitively unimpaired individuals. For this reason, the work group currently recommends against diagnostic testing in cognitively unimpaired individuals outside the context of observational or therapeutic research studies.
This recommendation would change in the future if disease-targeted therapies that are currently being evaluated in trials demonstrate a benefit in preventing cognitive decline and are approved for use in preclinical AD, they wrote.
They emphasize that the revised criteria are not intended to provide step-by-step clinical practice guidelines for clinicians. Rather, they provide general principles to inform diagnosis and staging of AD that reflect current science.
“This is just the beginning,” said Carrillo. “This is a gathering of the evidence to date and putting it in one place so we can have a consensus and actually a way to test it and make it better as we add new science.”
This also serves as a “springboard” for the Alzheimer’s Association to create formal clinical guidelines. “That will come, hopefully, over the next 12 months. We’ll be working on it, and we hope to have that in 2025,” Carrillo said.
The revised criteria also emphasize the role of the clinician.
“The biologically based diagnosis of Alzheimer’s disease is meant to assist, rather than supplant, the clinical evaluation of individuals with cognitive impairment,” the work group wrote in a related commentary published online on June 28 in Nature Medicine.
Recent diagnostics and therapeutic developments “herald a virtuous cycle in which improvements in diagnostic methods enable more sophisticated treatment approaches, which in turn steer advances in diagnostic methods,” they continued. “An unchanging principle, however, is that effective treatment will always rely on the ability to diagnose and stage the biology driving the disease process.”
Funding for this research was provided by the National Institutes of Health, Alexander family professorship, GHR Foundation, Alzheimer’s Association, Veterans Administration, Life Molecular Imaging, Michael J. Fox Foundation for Parkinson’s Research, Avid Radiopharmaceuticals, Eli Lilly, Gates Foundation, Biogen, C2N Diagnostics, Eisai, Fujirebio, GE Healthcare, Roche, National Institute on Aging, Roche/Genentech, BrightFocus Foundation, Hoffmann-La Roche, Novo Nordisk, Toyama, National MS Society, Alzheimer Drug Discovery Foundation, and others. A complete list of donors and disclosures is included in the original article.
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