MRI Monitoring Schedule for Leqembi (Lecanemab)
Obtain a baseline brain MRI before starting treatment, then perform MRI scans prior to the 5th, 7th, and 14th infusions 1.
Standard Monitoring Protocol
The FDA-approved schedule is straightforward:
- Baseline MRI: Must be obtained before initiating lecanemab treatment
- Pre-5th infusion MRI: Approximately 8-10 weeks into treatment (before dose #5)
- Pre-7th infusion MRI: Approximately 12-14 weeks into treatment (before dose #7)
- Pre-14th infusion MRI: Approximately 26-28 weeks into treatment (before dose #14)
This schedule is designed because ARIA typically occurs within the first 3-6 months of treatment, with the highest risk period being the initial 14 weeks 2.
Important Clinical Considerations
Earlier Monitoring May Be Warranted
Recent evidence suggests starting MRI monitoring before the third infusion to detect early ARIA cases 3. This is particularly relevant because:
- ARIA-E generally manifests within 3-6 months of treatment initiation 2
- Advanced imaging (7T MRI) can detect ARIA-H approximately 4 months earlier than standard 3T MRI 4
- In real-world practice, 24% of patients developed ARIA, with most cases detected during routine monitoring 5
High-Risk Populations Requiring Enhanced Vigilance
ApoE ε4 homozygotes (approximately 15% of AD patients) have substantially elevated ARIA risk 1:
- ARIA-E occurs in 34.5% of homozygotes versus 16.8% in heterozygotes 2
- Real-world data shows 44% of homozygotes developed ARIA versus 17% of heterozygotes 5
Enhanced clinical vigilance is mandatory during the first 14 weeks for all patients, but especially for ApoE ε4 carriers 1.
Symptomatic Monitoring
If any symptoms suggestive of ARIA develop at any time (headache, confusion, visual disturbances, focal neurological deficits, altered mental status), perform an immediate off-protocol MRI 1. Do not wait for the scheduled monitoring scan.
ARIA can mimic ischemic stroke—consider ARIA before administering thrombolytic therapy to any lecanemab-treated patient presenting with stroke-like symptoms 1.
After Initial Monitoring Period
Following the 14th infusion MRI, the FDA label does not mandate specific ongoing MRI surveillance intervals. However:
- Continue clinical monitoring for ARIA symptoms throughout treatment
- After 6 months, ARIA rates drop to levels similar to placebo 6
- Consider follow-up MRI 2-4 months after any ARIA detection to confirm resolution 1
Common Pitfalls to Avoid
Do not skip baseline MRI: Pre-existing microhemorrhages or superficial siderosis increase ARIA risk and may contraindicate treatment 1
Do not delay MRI if symptoms develop: Most ARIA cases (88%) manifest within 24 hours of infusion or shortly thereafter 5
Do not assume asymptomatic means safe: In real-world practice, 75% of ARIA cases were asymptomatic 5, yet still require treatment modification per protocol
Do not use inadequate imaging: Standard 3T MRI is acceptable, but 7T MRI provides superior ARIA-H detection if available 4
The monitoring schedule balances safety surveillance during the highest-risk period while avoiding excessive imaging burden once the critical early treatment phase is completed.