Intracranial metastasis as a mimic of amyloid-related imaging abnormalities.

This report describes a 79-year-old woman with biomarker-confirmed Alzheimer's disease who developed progressive vasogenic edema initially interpreted as amyloid-related imaging abnormalities (ARIA) with edema during lecanemab therapy, but was ultimately found to have multifocal intracranial metastases from recurrent papillary thyroid carcinoma. The serial neuroimaging highlights the diagnostic challenge of distinguishing ARIA from alternative causes of vasogenic edema in the era of anti-amyloid monoclonal antibody treatment. In addition, this case raises an important and underexplored question regarding whether anti-amyloid therapies may alter blood-brain barrier integrity in a manner that could influence metastatic spread in susceptible patients.