Imaging of neuroinflammation in dementia: a review

We are still very limited in management strategies for dementia, and establishing effective disease modifying therapies based on amyloid or tau remains elusive. Neuroinflammation has been increasingly implicated as a pathological mechanism in dementia and demonstration that it is a key event accelerating cognitive or functional decline would inform novel therapeutic approaches, and may aid diagnosis. Much research has therefore been done to develop technology capable of imaging neuroinflammation in vivo. The authors performed a systematic search of the literature and found 28 studies that used in vivo neuroimaging of one or more markers of neuroinflammation on human patients with dementia. The majority of the studies used positron emission tomography (PET) imaging of the TSPO microglial marker and found increased neuroinflammation in at least one neuroanatomical region in dementia patients, most usually Alzheimer's disease, relative to controls, but the published evidence to date does not indicate whether the regional distribution of neuroinflammation differs between dementia types or even whether it is reproducible within a single dementia type between individuals. It is less clear that neuroinflammation is increased relative to controls in mild cognitive impairment than it is for dementia, and therefore it is unclear whether neuroinflammation is part of the pathogenesis in early stages of dementia. Despite its great potential, this review demonstrates that imaging of neuroinflammation has not thus far clearly established brain inflammation as an early pathological event. Further studies are required, including those of different dementia subtypes at early stages, and newer, more sensitive, PET imaging probes need to be developed.