Research into Alzheimer's disease, which is celebrated as World Alzheimer's Day this Sunday, continues to advance, particularly in terms of diagnosis. But we are still far from knowing how to treat the disease, and fierce controversy remains.
– What are the new treatments worth?
This is the current major debate surrounding Alzheimer's disease, the most common form of dementia, with tens of millions of sufferers worldwide. Are new treatments, which have just been launched on the market, really worthwhile?
Eli Lilly's Kisunla (donanemab) and Biogen and Eisai's Leqembi (lecanemab) are, after several decades of fruitless research, the first to demonstrate such a marked effect in slowing symptoms.
But these benefits, only observed in patients at the beginning of the disease, remain very modest and, according to some experts, make almost no difference. However, these drugs can also cause serious cerebral hemorrhages.
Around the world, health authorities have made contrasting decisions on these treatments. The last country to make a decision was France, which decided in early September that it was inappropriate to reimburse them immediately.
While some disease control groups, particularly in the UK, are pushing hard for their approval, others are taking a more balanced position.
Leqembi is a "therapeutic innovation," but it is necessary to "keep in mind the intrinsic limitations" of this treatment, warned France Alzheimer, the main French organization in the field, in the spring.
– How to diagnose the disease?
More discreetly, another debate is stirring up specialists, with a growing divide between Europe and the United States: how to diagnose Alzheimer's disease?
Great advances have been made to enable very simple diagnosis, via a blood test which makes it possible to identify the “biological markers” of cerebral mechanisms involved in the disease.
This is a revolution compared to current tests, such as lumbar punctures, whose heavy and expensive nature effectively excludes many patients.
The first blood test has been authorized in the United States since May. This is not the case in Europe, but a large program is underway in the United Kingdom to assess whether these tests are a game-changer: a clinical trial has just been launched.
But will these tests ever be sufficient in themselves? Positions differ. At the end of 2024, the Alzheimer's Association, the leading organization in the United States, changed its criteria to consider biomarkers alone sufficient to make a diagnosis.
In Europe, specialists continue to consider that a thorough clinical examination will remain necessary to confirm the loss of cognitive and functional abilities.
"Many patients have abnormal biomarkers but never develop dementia," Dutch neurologist Edo Richard, who is also skeptical of new treatments, told AFP.
The two issues overlap because the defenders of Leqembi and Kisunla believe that early diagnosis, before marked clinical symptoms, could multiply the effect of these treatments.
– Can prevention be effective?
There is a consensus on the multiple risk factors for Alzheimer's disease and, more broadly, dementia. According to an expert report published in the Lancet in 2024, nearly half of cases are linked to identifiable factors: poor hearing, smoking, obesity, etc.
But experts disagree on the extent to which this observation can be translated into concrete and effective actions.
A growing body of research is testing the effectiveness of support programs that encourage patients to engage in regular physical activity and improve their diet. But these trials "have had little or no effect on cognitive decline or the development of dementia," Richard reports.
The latest study, published this summer in the journal JAMA, measured the cognitive abilities of patients in the United States who had undergone intensive support for two years. Their decline slowed slightly, but the effect remained modest.
For some observers, "it's not much," admitted French epidemiologist Cécilia Samieri in mid-September during a conference organized by the French foundation Vaincre Alzheimer.
But, for her, "it's already enormous." The researcher believes that only trials lasting ten or fifteen years could do justice to the effectiveness of interventions against disorders with such prolonged development.
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