Internal medicine

Pathology

Neuroscience

Progenitor cell

Disease

Dementia

Cognitive decline

Bioinformatics

Biology

Psychiatry

Cognition

Psychology

Stem cell

Radiation therapy

Genetics

Medicine

Nature Reviews Neurology

The majority of patients who receive radiotherapy for brain tumours go on to develop disability, but the pathophysiological mechanisms of radiation-associated cognitive decline remains poorly understood. Here, Makale and colleagues review animal model and patient data on the mechanisms of radiotherapy-associated CNS damage and posit that early damage — occurring before 6 months after irradiation — contributes to long-term cognitive disability. Standard treatment of primary and metastatic brain tumours includes high-dose megavoltage-range radiation to the cranial vault. About half of patients survive >6 months, and many attain long-term control or cure. However, 50–90% of survivors exhibit disabling cognitive dysfunction. The radiation-associated cognitive syndrome is poorly understood and has no effective prevention or long-term treatment. Attention has primarily focused on mechanisms of disability that appear at 6 months to 1 year after radiotherapy. However, recent studies show that CNS alterations and dysfunction develop much earlier following radiation exposure. This finding has prompted the hypothesis that subtle early forms of radiation-induced CNS damage could drive chronic pathophysiological processes that lead to permanent cognitive decline. This Review presents evidence of acute radiation-triggered CNS inflammation, injury to neuronal lineages, accessory cells and their progenitors, and loss of supporting structure integrity. Moreover, injury-related processes initiated soon after irradiation could synergistically alter the signalling microenvironment in progenitor cell niches in the brain and the hippocampus, which is a structure critical to memory and cognition. Progenitor cell niche degradation could cause progressive neuronal loss and cognitive disability. The concluding discussion addresses future directions and potential early treatments that might reverse degenerative processes before they can cause permanent cognitive disability.

Mechanisms of radiotherapy-associated cognitive disability in patients with brain tumours