A retired court stenographer aged 79 years with recent difficulty remembering the QWERTY keyboard layout and some increasing "forgetfulness" was referred to a neurologist for evaluation. Her neurologic examination was normal, but she scored 9 on the 6-Item Cognitive Impairment Test (6CIT; 0-7 out of 28 is considered normal). Brain MRI identified some reduction in gray matter volume in the frontal and cingulate cortices and white matter decline in the thalamic radiations. She was told that she was experiencing mild cognitive impairment (MCI), which may or may not progress to Alzheimer's dementia over time, and potential treatment options were discussed. Because her mother had died of "complications of Alzheimer's disease," she was particularly concerned about progression and decided to begin treatment with an anti-amyloid beta (Aβ) monoclonal antibody (mAb). Screening MRIs before the 7th and 12th infusions revealed no evidence of ARIA, she reported no noticeable progression of her forgetfulness, and the 6CIT remained unchanged over 18 months of treatment. After her 20th infusion she complained of a persistent headache and mild "dizziness," at which time axial brain MRI revealed ARIA-E on T2 FLAIR imaging with sulcal effusions ranging in size from 5 to 10 cm in the left temporal and parietal regions.