The 2023 FDA approval of lecanemab, a groundbreaking therapy shown to modestly slow the progression of Alzheimer’s disease, marked a significant milestone in dementia treatment. Yet, concerns about potential side effects — particularly brain swelling and bleeding — have made some patients and clinicians cautious about adopting the therapy.
Now, a retrospective study led by researchers at Washington University School of Medicine in St. Louis offers encouraging real-world evidence. Analyzing outcomes from 234 patients treated in their Memory Diagnostic Center, the team found that severe side effects requiring hospitalization occurred in only 1% of cases, consistent with results seen in controlled clinical trials.
Published May 12 in JAMA Neurology, the study highlights that patients in the earliest stage of Alzheimer’s, exhibiting very mild symptoms, face the lowest risk of complications. These findings provide valuable guidance for physicians and patients weighing the benefits and risks of lecanemab treatment.
“Lecanemab is the only approved medication that influences disease progression in early symptomatic Alzheimer’s,” said Barbara Joy Snider, MD, PhD, professor of neurology and co-senior author of the study. “Despite fears about side effects that can delay treatment, our clinic’s experience shows that with proper infrastructure and expertise, lecanemab can be safely administered in outpatient settings. This sets a model for other centers.”
Lecanemab is a monoclonal antibody therapy targeting amyloid plaques — abnormal protein deposits believed to trigger Alzheimer’s disease. Previous research led by WashU Medicine demonstrated that lecanemab extends patients’ independent living by approximately 10 months. Because amyloid buildup occurs early in Alzheimer’s, the drug is recommended primarily for those with very mild or mild cognitive symptoms.
The study revealed a striking contrast in side effect rates: only 1.8% of patients with very mild symptoms experienced adverse events, compared to 27% of those with mild symptoms. “Patients with the very mildest symptoms stand to gain the most benefit while facing the lowest risk,” Snider explained. “Delaying treatment due to hesitation can ironically increase risks. We hope these results help reshape conversations around this important medication.”
A major concern with lecanemab has been amyloid-related imaging abnormalities (ARIA), brain changes detectable by MRI scans that indicate swelling or bleeding. In clinical trials, 12.6% of participants experienced ARIA, though most cases were asymptomatic and resolved without intervention. Approximately 2.8% developed symptoms such as headache, confusion, nausea, or dizziness, and rare fatalities (around 0.2%) have been reported.
Since 2023, the Memory Diagnostic Center has administered lecanemab infusions every two weeks under careful monitoring. Patients undergo regular brain imaging to detect ARIA early. Those exhibiting symptomatic or significant asymptomatic ARIA have their treatment paused, and severe cases receive steroid therapy in hospital settings.
The retrospective review confirmed that side effect patterns in clinic patients closely matched clinical trial data. Among 11 patients who developed symptomatic ARIA, symptoms mostly resolved within months, and no deaths occurred.
“Most patients tolerate lecanemab well,” said Suzanne Schindler, MD, PhD, associate professor of neurology and co-senior author of the study. “This report should help clinicians and patients better understand the relatively low risks, particularly in those with very mild Alzheimer’s symptoms.”
As lecanemab and other novel therapies offer hope for slowing Alzheimer’s progression, this study reinforces the importance of early treatment and vigilant monitoring to optimize safety and outcomes.
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