ARIA surveillance is becoming the rate-limiting step in anti-amyloid care

ARIA - amyloid-related imaging abnormalities - describes a set of findings (edema, microhemorrhage, superficial siderosis) detected on MRI in patients receiving anti-amyloid antibodies. Most cases are asymptomatic. A minority require treatment pause or discontinuation. A small subset are serious.

Surveillance is mandatory under both the lecanemab and donanemab labels, and the protocol-defined MRI cadence is non-trivial: a baseline plus several follow-ups in the first months of therapy. Health systems that have published their experience consistently flag two issues:

• Imaging slot availability. Routine outpatient MRI in most US health systems is not scheduled around drug-monitoring protocols.
• Interpretation and decision-making. Identifying ARIA on MRI is straightforward; deciding whether to continue, pause, or stop therapy requires neurology judgment that is unevenly available outside specialty centers.

The practical consequence is that ARIA infrastructure - not biology - often determines who can receive therapy and where. For the post-launch picture of how ARIA rates are actually behaving in routine use, see our companion Signal on real-world ARIA rates from registries.

A worth-noting forward implication: the subcutaneous formulations of the anti-amyloid antibodies decompress the infusion-chair side of the rollout, but they do not change the MRI surveillance requirement - ARIA is a class effect of the underlying biology, not the delivery route. As the infusion bottleneck eases, the MRI/neurology bottleneck becomes proportionally more binding, not less.