A woman aged 68 years with mild dementia due to Alzheimer's disease experienced a reduction in Clinical Dementia Rating-Sum of Boxes (CDR-SB) 18 from 3.2 to 1.2 and a reduction in amyloid burden on PET of -55.1 centiloids over a treatment period of 18 months while enrolled in a phase 3 trial of lecanemab.1 She was confirmed to have participated in the active treatment group and consented to enter an open-label extension of the study during which she continued to receive 10 mg/kg of lecanemab every 2 weeks. Occurrences of ARIA were monitored throughout the trial by brain MRI performed at weeks 9, 13, 27, 53, 79, and 91 for safety monitoring. At Week 79, surveillance MRI revealed ARIA-H on gradient recalled-echo/T2* image, with several punctate microhemorrhages in the right parietal region. She had no symptoms suggestive of ARIA-H. The study protocol called for subjects who developed symptomatic ARIA‐H to be temporarily stopped from study drug administration.2 Because the episode of ARIA-H in this patient was determined to be mild (1-4 new microhemorrhages),3,4 she continued treatment and no new ARIA-H was identified at 1-month follow-up MRI. After lecanemab received FDA approval, she transitioned to treatment outside the study extension.
