Amyloid-related imaging abnormalities in patients with Alzheimer's disease treated with bapineuzumab: a retrospective analysis

Background: Amyloid-related imaging abnormalities (ARIA) have been reported in patients with Alzheimer's disease treated with bapineuzumab, a humanised monoclonal antibody against amyloid β. ARIA include MRI signal abnormalities suggestive of vasogenic oedema and sulcal effusions (ARIA-E) and microhaemorrhages and haemosiderin deposits (ARIA-H). Our aim was to investigate the incidence of ARIA during treatment with bapineuzumab, and evaluate associated risk factors.

Methods: Two neuroradiologists independently reviewed 2572 fluid-attenuated inversion recovery (FLAIR) MRI scans from 262 participants in two phase 2 studies of bapineuzumab and an open-label extension study. Readers were masked to the patient's treatment, APOE ɛ4 genotype, medical history, and demographics. Patients were included in risk analyses if they had no evidence of ARIA-E in their pre-treatment MRI, had received bapineuzumab, and had at least one MRI scan after treatment. We used Kaplan-Meier survival analysis to examine the distribution of incident ARIA-E from the start of bapineuzumab treatment and proportional hazards regression models to assess risk factors associated with ARIA.

Findings: 210 patients were included in the risk analyses. 36 patients (17%) developed ARIA-E during treatment with bapineuzumab; 15 of these ARIA-E cases (42%) had not been detected previously. 28 of these patients (78%) did not report associated symptoms. Adverse events, reported in eight symptomatic patients, included headache, confusion, and neuropsychiatric and gastrointestinal symptoms. Incident ARIA-H occurred in 17 of the patients with ARIA-E (47%), compared with seven of 177 (4%) patients without ARIA-E. 13 of the 15 patients in whom ARIA were detected in our study received additional treatment infusions while ARIA-E were present, without any associated symptoms. Occurrence of ARIA-E increased with bapineuzumab dose (hazard ratio [HR] 2·24 per 1 mg/kg increase in dose, 95% CI 1·40-3·62; p=0·0008) and presence of APOE ɛ4 alleles (HR 2·55 per allele, 95% CI 1·57-4·12; p=0·0001).

Interpretation: ARIA consist of a spectrum of imaging findings with variable clinical correlates, and some patients with ARIA-E remain asymptomatic even if treatment is continued. The increased risk of ARIA among APOE ɛ4 carriers, its association with high bapineuzumab dose, and its timecourse in relation to dosing suggest an association between ARIA and alterations in vascular amyloid burden.

Funding: Elan Corporation, Janssen Alzheimer Immunotherapy, Wyeth Pharmaceuticals, and Pfizer.