<scp>Magnetic resonance imaging</scp> eligibility for anti‐amyloid monoclonal antibody treatment for Alzheimer disease: a single‐centre retrospective review for service planning

Dementia is projected as the leading cause of mortality in Australia.1 Anti-amyloid monoclonal antibody therapies are the first disease-modifying treatments for Alzheimer disease (AD)2 and are poised to transform the landscape of dementia management. The US Food and Drug Administration (FDA) approved aducanumab (discontinued in 2024), lecanemab and donanemab following trial evidence for effective amyloid clearance and a modest yet statistically significant attenuation of disease progression.3, 4 These therapies are associated with serious adverse events: amyloid-related imaging abnormalities (ARIAs) with oedema or haemosiderin deposition from microhaemorrhages or superficial siderosis.5 The initial decision of Australia's Therapeutic Goods Administration (TGA) was not to register lecanemab, partially based on safety risks outweighing marginal benefits.6 Donanemab was approved by the TGA in May 2025 and lecanamab in September 2025. A US cross-sectional study of patients with early AD estimated that treatment eligibility would be limited (8–17%) because of stringent eligibility criteria especially among older adults with multiple co-morbidities.7 The Australian healthcare system will need to increase infrastructure capacity and workforce skills to support the provision of infusions, investigations such as magnetic resonance imaging (MRI) and biomarkers and ensure drug safety monitoring.5 Given the high costs of treatment, drug administration and clinical monitoring, research on real-world eligibility is needed for forecasting potential drug demand and service requirements. We conducted a single-centre retrospective cross-sectional study evaluating a cohort of patients with AD presenting to a cognitive neurology service, specialising in younger-onset dementia, within a tertiary metropolitan hospital from 1 January 2007 to 8 August 2024. Patient eligibility for monoclonal antibody treatment was determined based on MRI eligibility criteria employed in clinical trials, identifying patients at high risk for the development of ARIAs who would be ineligible. Markers of small vessel disease (white matter hyperintensities, prior stroke) or cerebral amyloid angiopathy (cerebral microhaemorrhages, superficial cortical siderosis) were used in trials as exclusion criteria.8 Patients were identified via a search for AD diagnosis. Hospital imaging databases were searched for prior MRI scans and reviewed by two reviewers independently. Two hundred and ninety-three patients with AD or amnestic mild cognitive impairment were identified, with 235 (80%) having MRI brain available. Patient demographics are documented in Table 1. Among those with MRI of the brain, 196 (72%) had complete sequences and 135 (58%) would qualify for monoclonal antibody therapy. It was not possible to determine treatment eligibility in 39 (17%) patients who had not had complete MRI sequences. Fifty-nine patients (25%) were deemed ineligible (Table 2). This study was limited by its retrospective nature and missing data. Scans were diagnostic rather than following trial protocols. We did not look at other exclusion criteria, e.g. Mini-Mental State Examination (MMSE), co-morbidities or concomitant treatment with anticoagulation, which would lower this study's estimate. It is acknowledged that with a mean MMSE score of 20, some patients with lower MMSE scores may have been excluded from treatment due to more advanced dementia. Further, both susceptibility-weighted imaging (SWI) and gradient-recalled echo were accepted, which may have increased eligibility numbers compared with SWI alone. Conversely, the TGA criteria have limited eligibility to two microbleeds, which would decrease eligibility compared with the original trial criteria. Due to limited funded testing in the public system, patients were also not assessed for APOE Ɛ4 homozygosity, which restricts treatment eligibility due to increased ARIA propensity.9, 10 Representing a tertiary memory service patient population, the average patient age was relatively young with higher numbers of atypical AD; however, AD subtype has not been shown to influence the proportion of patients with microbleeds at baseline and was not thought to influence eligibility. A single-centre, tertiary metropolitan experience will affect the broader applicability to settings with different patient demographics, dementia prevalence, clinical characteristics and healthcare processes. Our population may have had a higher utilisation of MRI scans. Further scoping research is warranted for understanding the real-world practical and economic implications of monoclonal antibody therapies on Australian healthcare services. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.