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Monitoring ARIA (Brain Swelling and Bleeding) with Anti-Amyloid Drugs

This article explains what ARIA (amyloid-related imaging abnormalities) is, why it happens with lecanemab and donanemab, and how it is monitored through regular brain MRIs. It covers the specific risks, including who is at higher risk, what symptoms to watch for, and the concrete steps you and your clinician will take to keep your loved one safe. You are not alone in navigating this — there are clear protocols and real-world data showing these risks can be managed with careful monitoring.

Key points

  • ARIA (brain swelling and bleeding) is a known risk of lecanemab and donanemab, but it is monitored with regular brain MRIs and is usually mild.
  • Before starting treatment, a baseline MRI and APOE e4 genetic testing are recommended to assess risk.
  • People with the APOE e4 gene or those taking blood thinners are at higher risk and need closer monitoring.
  • Watch for symptoms like new headache, confusion, vision changes, dizziness, weakness, or seizures — report them immediately.
  • Do not skip MRIs, stop blood thinners on your own, or ignore new symptoms.
  • Real-world data shows that with proper monitoring, the safety of these drugs is comparable to or better than clinical trials.

What is ARIA and Why Does It Happen?

ARIA stands for amyloid-related imaging abnormalities. It is a known side effect of anti-amyloid drugs like lecanemab and donanemab. ARIA comes in two forms: ARIA-E, which is brain swelling (edema), and ARIA-H, which is small or large brain bleeds (hemorrhage). These happen because the drugs trigger the immune system to clear amyloid plaques from the brain, and this immune response can cause temporary inflammation or small blood vessel leaks. Most ARIA is mild and goes away on its own, but in rare cases it can become serious, leading to seizures, large strokes, or even death. The risk is highest in people who carry the APOE e4 gene, which is why the FDA recommends genetic testing before starting treatment.

How is ARIA Monitored?

Monitoring for ARIA is built into the treatment protocol. Before starting the drug, your clinician will order a baseline brain MRI to check for any pre-existing microhemorrhages, old strokes, or other conditions that could increase risk. If the MRI shows more than four microhemorrhages, a large hemorrhage, or a major old stroke, the patient is generally not eligible for these drugs. Once treatment begins, regular MRIs are scheduled — typically before the 5th, 7th, and 14th infusions, and then periodically after that. These scans look for any new swelling or bleeding. The goal is to catch ARIA early, before it causes symptoms, so the clinician can pause the drug or adjust the dose. Real-world data from clinics and memory centers shows that this monitoring approach keeps safety comparable to or better than the clinical trials.

Who is at Higher Risk?

People with the APOE e4 gene variant are at higher risk for ARIA, especially those with two copies of the gene. Additionally, anyone taking blood thinners (anticoagulants) has an increased risk of brain bleeding while on these drugs. Other conditions that raise bleeding risk — such as a history of bleeding disorders, recent head trauma, or uncontrolled high blood pressure — also increase the chance of ARIA-H. Because of this, the pre-treatment evaluation includes a detailed medical history, a neurological exam, and the baseline MRI. If you or your loved one takes a blood thinner, it is essential to discuss this with the clinician before starting treatment. The decision to stop or continue a blood thinner must be made by the prescribing doctor, never on your own.

General caregiving information, not medical advice. Check medications and major care changes with your clinician.

Step-by-step

  1. Step 1: Before starting the drug, ask your clinician about APOE e4 genetic testing. The FDA recommends this test to understand your loved one's risk of ARIA. If the result shows one or two copies of the e4 gene, the clinician will discuss the higher risk and may adjust the monitoring schedule.

  2. Step 2: Schedule a baseline brain MRI. This scan checks for any existing microhemorrhages, old strokes, or other brain abnormalities. The MRI must show no more than four microhemorrhages and no large hemorrhages or major strokes for the patient to be eligible.

  3. Step 3: Review all current medications with the clinician, especially blood thinners (like warfarin, apixaban, rivaroxaban, or clopidogrel). If your loved one takes a blood thinner, the clinician will weigh the risk of ARIA against the risk of stopping the blood thinner. Do not stop any blood thinner without direct instruction from the prescribing doctor.

  4. Step 4: During treatment, keep a calendar of infusion dates and MRI dates. The standard protocol includes MRIs before the 5th, 7th, and 14th infusions, and then periodically after that. Ask your clinic for a written schedule so you can plan ahead.

  5. Step 5: Watch for symptoms of ARIA between MRIs. These include new or worsening headache, confusion, vision changes (blurred vision, double vision), dizziness, nausea, vomiting, weakness on one side of the body, trouble speaking, or seizures. If any of these occur, contact the clinician immediately — do not wait for the next scheduled MRI.

  6. Step 6: At each infusion visit, ask the nurse or doctor if the latest MRI was reviewed and whether there were any signs of ARIA. If ARIA is detected, the clinician will typically pause the drug and repeat the MRI in a few weeks to see if the swelling or bleeding has resolved. Treatment may be restarted at a lower dose or discontinued depending on severity.

  7. Step 7: Keep a symptom diary. Write down any new symptoms, even if they seem minor, and note the date and time. Share this diary with the clinician at every visit. This helps catch ARIA early, especially if symptoms are subtle.

  8. Step 8: If ARIA is detected and the drug is paused, follow the clinician's instructions for the next MRI. Most mild ARIA resolves on its own within a few weeks. During this time, avoid activities that could increase the risk of head injury, such as contact sports or falls. Use assistive devices (walkers, grab bars) if needed.

  9. Step 9: After the drug is restarted (if appropriate), continue the same monitoring schedule. Real-world data shows that most patients who experience mild ARIA can safely resume treatment. However, if ARIA is severe or recurrent, the clinician may recommend stopping the drug permanently.

  10. Step 10: Stay in touch with the clinic's care coordinator. Many centers have a dedicated nurse or coordinator who tracks MRI schedules and can answer questions between visits. Ask for their direct contact information.

What not to do

  • Do not skip or delay an MRI because your loved one feels fine. ARIA can be present without any symptoms. The MRI is the only way to detect it early. Skipping a scan could allow a small bleed to become a large one.

  • Do not stop a blood thinner on your own before starting the drug. This could increase the risk of a stroke or heart attack. Always discuss with the clinician who prescribed the blood thinner first.

  • Do not assume that a headache or dizziness is just a normal part of aging or dementia. These can be early signs of ARIA. Always report new symptoms to the clinician promptly.

  • Do not downplay the risk of ARIA to your loved one or yourself. While the risk of serious ARIA is low (about 1-4% absolute risk of death in some studies), it is real. Acknowledge the risk and follow the monitoring plan carefully.

  • Do not rely on over-the-counter pain relievers like ibuprofen or aspirin for headaches during treatment without checking with the clinician. These can increase bleeding risk and may mask ARIA symptoms.

Practical tools

  • Symptom Diary Template

    Create a simple log with columns for Date, Time, Symptom (e.g., headache, confusion, vision change), Severity (mild/moderate/severe), and Action Taken. Keep it in a notebook or on your phone. Bring it to every clinician visit. This helps catch ARIA early and provides a clear record for the care team.

  • MRI Schedule Card

    Ask the clinic for a printed card or a digital reminder that lists the dates of all upcoming MRIs. Tape it to your refrigerator or set phone reminders. The standard schedule is before the 5th, 7th, and 14th infusions, but your clinic may adjust based on risk. Never miss a scheduled MRI.

  • Phrases to Say to the Clinician

    Use these exact questions: 'What was the result of the latest MRI? Were there any signs of ARIA?' 'Is my loved one at higher risk because of the APOE e4 gene?' 'Are there any medications we should stop or avoid to lower bleeding risk?' 'What symptoms should I call you about immediately?'

  • Fall Prevention Checklist

    Because ARIA can cause dizziness or weakness, reduce fall risk: remove loose rugs, install grab bars in the bathroom, use a walker if needed, ensure good lighting, and keep pathways clear. If your loved one has a fall, call the clinician immediately — even if there is no visible injury — because a fall could trigger a brain bleed.

  • Emergency Contact Card

    Write down the clinic's after-hours number, the neurologist's direct line, and the nearest emergency room that has MRI capability. Keep this card in your wallet and on the refrigerator. If ARIA symptoms appear, you will not have to search for numbers.

  • Medication List for the Clinician

    Before each visit, update a list of all medications, including over-the-counter drugs, supplements, and blood thinners. Include dosages and how often they are taken. This helps the clinician quickly assess bleeding risk and avoid drug interactions.

Discuss with your clinician

Ask your clinician: 'Should my loved one get the APOE e4 genetic test before starting treatment, and what will the results mean for our risk and monitoring plan?'

Ask your clinician: 'My loved one takes [name of blood thinner]. How should we manage this medication during treatment? Should we stop it, switch it, or continue it?'

Ask your clinician: 'What is the exact schedule of MRIs for this drug, and what happens if a scan shows ARIA? Will the drug be paused, and for how long?'

Ask your clinician: 'Are there any over-the-counter medications or supplements we should avoid to lower bleeding risk, such as ibuprofen, aspirin, fish oil, or ginkgo biloba?'

Ask your clinician: 'What symptoms should I call you about immediately, and what is the after-hours number? When should I go to the emergency room instead of waiting for a clinic appointment?'

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