FDA to Recommend Additional, Earlier MRI Monitoring for Patients with Alzheimer’s Disease Taking Leqembi (Lecanemab)

Why It Matters

By detecting brain swelling earlier, the FDA’s guidance could prevent fatal outcomes and preserve confidence in Leqembi, a cornerstone therapy in the emerging Alzheimer’s‑treatment market.

Key Takeaways

• FDA adds MRI before 3rd Leqembi infusion.
• 101 serious ARIA‑E cases identified, six fatal.
• Two serious ARIA‑E cases occurred between 2nd‑3rd infusion.
• Early detection may prompt treatment pause or stop.
• Monitoring now includes scans at infusions 3,5,7,14.

Pulse Analysis

Leqembi (lecanemab) entered the U.S. market in 2023 as the first disease‑modifying antibody approved for early Alzheimer’s disease, offering a modest slowdown of cognitive decline. However, its mechanism of clearing amyloid plaques carries a well‑documented safety signal: amyloid‑related imaging abnormalities with edema (ARIA‑E), which can manifest as brain swelling, seizures, or even death. The FDA’s drug‑safety communication on August 28, 2025 reflects growing concern that the existing MRI schedule—at the 5th, 7th, and 14th infusions—may miss early, potentially fatal events.

The agency’s review uncovered 101 serious ARIA‑E reports, including six fatalities, with two cases already present between the second and third infusions and a further 22 between the third and fourth. Because ARIA‑E can progress rapidly after initial detection, the FDA now mandates an additional MRI between the second and third lecanemab doses. Early imaging provides clinicians a window to pause or discontinue therapy before symptoms escalate, aligning treatment decisions with patient safety and potentially reducing the incidence of fatal outcomes.

For manufacturers and payers, the updated monitoring schedule adds logistical complexity and cost, but it also strengthens the therapeutic’s risk‑management profile, which could sustain its market uptake amid competition from emerging anti‑amyloid agents. Neurologists will need to coordinate baseline scans, schedule the new interim MRI, and educate patients and caregivers about warning signs such as headache or confusion. As real‑world evidence accumulates, the industry will watch whether earlier detection translates into lower mortality rates and whether similar monitoring protocols become standard for other amyloid‑targeting drugs.