A Severe Symptomatic Case of Amyloid-Related Imaging Abnormalities After Donanemab Infusion.

Amyloid-related imaging abnormalities (ARIA) are known complications of anti-amyloid monoclonal antibody therapy for Alzheimer's disease. Although many cases are asymptomatic, severe presentations can mimic stroke or toxic encephalopathy. This case highlights a rare presentation of ARIA with myoclonic movements and acute encephalopathy following donanemab infusion. We report a 75-year-old woman with Alzheimer's disease who developed acute confusion, hallucinations, and involuntary movements one day after her sixth donanemab infusion. Stroke workup was negative. MRI demonstrated findings consistent with both ARIA-E and ARIA-H. She was treated with high-dose intravenous methylprednisolone, followed by an oral prednisone taper, which resulted in gradual neurological improvement. Clinicians must maintain a high suspicion for ARIA in patients receiving anti-amyloid therapy who present with acute neurologic decline. Early MRI evaluation and prompt corticosteroid treatment may improve outcomes.