Leqembi and Kisunla are paused when amyloid-related imaging abnormalities (ARIA) are detected on brain MRI scans, when imaging shows worsening of ARIA already present, or when symptoms emerge that suggest ARIA—typically during the first year of treatment. These drugs target amyloid plaques, the protein buildup associated with early Alzheimer’s disease, but this same mechanism can trigger inflammation or microhemorrhages in the brain, collectively called ARIA. For example, a patient might begin treatment successfully, undergo a scheduled MRI three months in, and the scan could reveal brain swelling (ARIA-E) that wasn’t visible before, prompting the medical team to pause infusions until the inflammation resolves.
The decision to pause is not automatic—it depends on the severity of ARIA, whether symptoms are present, and how quickly changes appear. Both leqembi and kisunla share the same safety concern with ARIA because they work through similar mechanisms. Doctors monitor for ARIA throughout the first year and sometimes beyond, knowing that the imaging findings can develop weeks or months after infusions begin. Treatment interruption gives the brain time to stabilize, often allowing restart once ARIA improves.
Medical information disclaimer: This article is for general educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a physician or other qualified health professional about symptoms, medications, tests, or treatment decisions.
Table of Contents
- What Triggers a Pause During Leqembi or Kisunla Treatment?
- Understanding ARIA-E and ARIA-H—The Two Forms
- How ARIA Is Detected and Monitored
- Making the Pause Decision—Which Patients and Which Severity Levels?
- Risk Factors and Why Some Patients Develop ARIA More Than Others
- What Happens During a Treatment Pause?
- Restarting Treatment After ARIA Resolve
- Frequently Asked Questions
What Triggers a Pause During Leqembi or Kisunla Treatment?
Treatment is typically paused when three main scenarios occur: asymptomatic aria detected on routine MRI, symptomatic ARIA, or worsening of previously seen ARIA on follow-up imaging. Asymptomatic ARIA is the most common—a patient feels fine but the MRI shows edema or microhemorrhages. Symptomatic ARIA means the patient has developed headaches, cognitive changes, confusion, vision problems, or balance issues that correlate with imaging findings. The pausing decision also depends on severity grades, which radiologists assign based on the extent and location of the abnormality.
Cognitive symptoms are particularly important markers because they indicate the ARIA is affecting brain function. A patient might report new difficulty remembering conversations, increased confusion, or personality changes in the weeks after these symptoms appear on MRI. Even if a patient is asymptomatic, many treatment centers pause if ARIA is moderate to severe, playing it safe to prevent progression. Mild, asymptomatic ARIA sometimes leads to closer monitoring and continued treatment, though practice varies.
Understanding ARIA-E and ARIA-H—The Two Forms
ARIA-E (amyloid-related imaging abnormalities – edema) is brain swelling, visible as increased water content on mri, often appearing around the areas of amyloid plaques. ARIA-H (amyloid-related imaging abnormalities – microhemorrhages) involves tiny bleeds in brain tissue, seen as small dark dots on certain MRI sequences. A patient might experience ARIA-E alone, ARIA-H alone, or both simultaneously. When both occur, the risk of neurological symptoms rises, and pausing is more likely.
ARIA-E typically appears within the first few months of treatment and can resolve in weeks to months after pausing. ARIA-H generally emerges later and resolves more slowly. The main limitation with ARIA-H is that it can occasionally result in permanent microhemorrhages that show on future scans even after treatment pause, though usually without permanent cognitive damage. Some centers follow a more aggressive pause protocol for ARIA-H because the microhemorrhages, once established, cannot be reversed—only their progression can be halted.
How ARIA Is Detected and Monitored
Regular MRI screening is the only way to detect ARIA reliably, so both leqembi and kisunla protocols include mandatory baseline MRI before treatment starts, then scans at set intervals—often at 1 month, 3 months, 6 months, and 12 months, depending on the treatment center. Some scans may be moved earlier if a patient develops new symptoms. Standard MRI sequences used include FLAIR for edema detection and T2*-weighted imaging for microhemorrhages. An experienced radiologist interprets each scan for the presence, location, and severity of ARIA.
Clinical teams also rely on caregiver and patient reports of new symptoms between scans. Persistent headache, sudden confusion, or changes in behavior warrant urgent MRI to check for ARIA, even if a scan is not scheduled. This is why patients and caregivers receive education about warning signs before treatment begins. The downside is that MRI is costly and time-intensive, limiting how frequently some patients can be scanned, which means some ARIA may be missed or detected later than ideal.
Making the Pause Decision—Which Patients and Which Severity Levels?
Not every case of ARIA found on MRI leads to a pause. A small, asymptomatic ARIA-E in one brain region might allow continued treatment with increased imaging frequency, while a large ARIA-E spanning multiple areas or a symptomatic ARIA-H almost always triggers a pause. The radiologist’s severity rating—mild, moderate, or severe—is central to this decision. Moderate and severe ARIA typically warrant pause; mild asymptomatic ARIA sometimes does not, though many centers lean toward pausing anyway.
Patient age, overall health, cognitive baseline, and ApoE4 genetic status influence how aggressively teams respond. An older patient or one who is ApoE4-positive (a genetic risk factor for Alzheimer’s) may have ARIA paused sooner than a younger patient with the same imaging findings. The presence of symptoms always tips the scale toward pausing, regardless of severity grade. One key tradeoff is that continued treatment offers ongoing amyloid reduction and potential cognitive benefit, while pausing sacrifices that benefit to reduce ARIA risk.
Risk Factors and Why Some Patients Develop ARIA More Than Others
Certain characteristics increase ARIA likelihood. Carrying the ApoE4 gene variant, having severe baseline amyloid burden, older age, and presence of microinfarcts or brain atrophy on baseline MRI all correlate with higher ARIA risk. Some patients never develop ARIA despite treatment, while others do within weeks.
Rapid infusion rate and higher cumulative drug doses are also risk factors, which is why dose escalation is gradual in these protocols. A critical limitation is that we cannot reliably predict which individual patient will develop ARIA before starting treatment, so close monitoring is essential for everyone. Even patients at seemingly low risk can develop ARIA unexpectedly. Additionally, stopping treatment to manage ARIA means losing the cognitive benefit that the amyloid-targeting drug provides, creating a genuine medical dilemma for patients who might benefit most from the drug but are at high ARIA risk.
What Happens During a Treatment Pause?
During a pause, infusions stop, and the patient continues routine follow-up MRI and clinical visits to track whether ARIA resolves. Some patients receive supportive care such as corticosteroids in moderate to severe ARIA-E cases, though evidence for their benefit is mixed. Most ARIA-E improves or resolves within weeks to months without intervention beyond stopping the drug. ARIA-H typically takes longer to resolve or may not resolve completely, leaving trace microhemorrhages visible on future scans.
Many patients eventually resume treatment after ARIA improves, though the timing and safety of restart varies. Some restart at the same dose and schedule; others restart slowly or at lower doses. A patient who developed ARIA-E early might restart, complete treatment, and reach target dose despite the interruption. One example is a patient who paused after developing moderate ARIA-E at month three, resumed at month six once edema had resolved, and ultimately received the full treatment course over a longer timeline than planned.
Restarting Treatment After ARIA Resolve
Restarting leqembi or kisunla after ARIA requires careful clinical judgment and usually continued close MRI monitoring. Some patients who pause and resolve ARIA successfully complete treatment after restart, suggesting the ARIA was a temporary response that could be managed. Others do not restart due to patient or physician preference for avoiding further ARIA risk.
If restart occurs, it may be at the same schedule or with modified dosing—for instance, slower infusions or lower doses to reduce ARIA risk on re-exposure. The medical record from the first treatment attempt is crucial; a patient who developed severe ARIA-H might not be a candidate for restart, while one with mild, asymptomatic ARIA-E might be. Data on long-term outcomes of patients who pause, resolve ARIA, and restart are still accumulating, as these drugs are relatively new. Treatment decisions must balance the risk of ARIA recurrence against the cognitive benefit the patient could gain from completing treatment.
Frequently Asked Questions
Can ARIA cause permanent brain damage?
ARIA-E (edema) usually resolves without permanent injury. ARIA-H (microhemorrhages) can leave small permanent marks on MRI but rarely cause lasting cognitive loss; pausing treatment prevents further bleeding.
How often is MRI needed while taking these drugs?
Standard protocols include MRI at baseline, 1 month, 3 months, 6 months, and 12 months. More frequent scans occur if symptoms develop or ARIA is detected.
What symptoms should prompt urgent evaluation?
New or severe headache, sudden confusion, vision changes, loss of balance, or behavioral changes warrant immediate contact with the treatment team and possibly urgent MRI.
Can I restart treatment after ARIA?
Some patients do restart successfully after ARIA resolves, though not all. The decision depends on ARIA severity, patient preference, and doctor judgment.
Do genetic factors predict who will get ARIA?
Carrying ApoE4 and having high amyloid burden increase ARIA risk, but we cannot reliably predict ARIA in any individual patient before treatment begins.
Is ARIA more common with Leqembi or Kisunla?
Both drugs show comparable ARIA rates in their respective trials; ARIA is an expected potential side effect of any anti-amyloid monoclonal antibody at this stage of development.
