New Alzheimer's Immunotherapy May Cause Brain Shrinkage – and That's Okay

**UCL researchers** have discovered that the slight brain shrinkage observed in Alzheimer's patients treated with new immunotherapies like lecanemab is likely a result of the drug's effectiveness in removing amyloid plaques, rather than the loss of brain cells. This discovery challenges previous concerns about potential toxicity and introduces the term 'amyloid-removal-related pseudo-atrophy' (ARPA) to describe this phenomenon. Alzheimer's patients typically show brain volume loss due to neuron degradation, but the volume changes noted in trials of amyloid-targeting drugs were consistent with plaque removal. **Professor Nick Fox**, a senior author, emphasized that this finding is a significant therapeutic breakthrough in treating Alzheimer's. **Dr. Christopher Belder** advocates for better clinical trial reporting and further evaluation of these volume changes. Despite its therapeutic promise, the cost-effectiveness of lecanemab is under review by NICE, potentially impacting its availability through the NHS. Such studies underscore the complexity and evolving nature of Alzheimer's treatment, pointing to the need for informed consideration of benefits versus costs in healthcare decisions.