Reduced diffusion associated with amyloid-related imaging abnormalities in three patients treated with donanemab

Amyloid-related imaging abnormalities (ARIA) with edema (ARIA-E) and with hemorrhage (ARIA-H) are common adverse effects of amyloid-targeting therapies (ATT), characterized on MRI by T2/fluid-attenuated inversion recovery (FLAIR) hyperintensities and susceptibility-sensitive hypointensities, respectively. ARIA resulting from ATT is not commonly associated with reduced diffusion or acute infarcts. In this case series, we describe three patients with mild cognitive impairment due to Alzheimer's disease (AD) - a 75-year-old woman, a 74-year-old woman, and an 80-year-old man (APOE ε3/ε3, ε4/ε4, and ε3/ε4, respectively) - who developed ARIA accompanied by transient foci of reduced diffusion within the first six months of donanemab treatment, without permanent T2/FLAIR correlates. The diffusion-restricting lesions may represent ischemic infarcts, although the lack of permanent T2/FLAIR correlate is atypical. Clinicians should be aware that reduced diffusion may accompany ARIA. The course can be highly dynamic, and both the clinical presentation and management implications may vary.