Two antiamyloid drugs were recently approved by the Food and Drug Administration for treating early-stage Alzheimer’s disease (AD). In trials of both lecanemab (Leqembi) and donanemab, a long-held neuropharmacologic dream was realized: Most amyloid plaques – the primary pathologic marker for AD – were eliminated from the brains of patients with late pre-AD or early AD.
Implications for the amyloid hypothesis
The reduction of amyloid plaques has been argued by many scientists and clinical authorities to be the likely pharmacologic solution for AD. These trials are appropriately viewed as a test of the hypothesis that amyloid bodies are a primary cause of the neurobehavioral symptoms we call AD.
In parallel with that striking reduction in amyloid bodies, drug-treated patients had an initially slower progression of neurobehavioral decline than did placebo-treated control patients. That slowing in symptom progression was accompanied by a modest but statistically significant difference in neurobehavioral ability. After several months in treatment, the rate of decline again paralleled that recorded in the control group. The sustained difference of about a half point on cognitive assessment scores separating treatment and control participants was well short of the 1.5-point difference typically considered clinically significant.
A small number of unexpected and unexplained deaths occurred in the treatment groups. Brain swelling and/or micro-hemorrhages were seen in 20%-30% of treated individuals. Significant brain shrinkage was recorded. These adverse findings are indicative of drug-induced trauma in the target organ for these drugs (i.e., the brain) and were the basis for a boxed warning label for drug usage. Antiamyloid drug treatment was not effective in patients who had higher initial numbers of amyloid plaques, indicating that these drugs would not measurably help the majority of AD patients, who are at more advanced disease stages.
These drugs do not appear to be an “answer” for AD. A modest delay in progression does not mean that we’re on a path to a “cure.” Treatment cost estimates are high – more than $80,000 per year. With requisite PET exams and high copays, patient accessibility issues will be daunting.
Of note, To the contrary, they add strong support for the counterargument that the emergence of amyloid plaques is an effect and not a fundamental cause of that progressive loss of neurologic function that we ultimately define as “Alzheimer’s disease.”
Time to switch gears
The more obvious path to winning the battle against this human scourge is prevention. A recent analysis published in The Lancet argued that about 40% of AD and other dementias are potentially preventable. I disagree. I believe that 80%-90% of prospective cases can be substantially delayed or prevented. Studies have shown that progression to AD or other dementias is driven primarily by the progressive deterioration of organic brain health, expressed by the loss of what psychologists have termed “cognitive reserve.” Cognitive reserve is resilience arising from active brain usage, akin to physical resilience attributable to a physically active life. Scientific studies have shown us that an individual’s cognitive resilience (reserve) is a greater predictor of risk for dementia than are amyloid plaques – indeed, greater than any combination of pathologic markers in dementia patients.