The pathogenic role of gut microbiota dysbiosis in Alzheimer's disease: a narrative review of neuroimaging evidence.

Dementia is a progressive and ultimately life-limiting condition that represents a major cause of disability worldwide. Alzheimer’s disease (AD) is the most prevalent form of dementia that constitutes approximately 60–70% of cases and is marked by progressive cognitive and functional decline. Neuropathologically, AD is defined by extracellular amyloid-β (Aβ) plaque accumulation and intracellular deposition of hyperphosphorylated tau. Despite extensive research, the mechanisms underlying AD pathogenesis remain incompletely understood. Increasing evidence implicates gut microbiota dysbiosis as a contributing factor via the MGBA, a bidirectional communication system linking gastrointestinal and central nervous system function. To elucidate this relationship, we conducted a narrative review of neuroimaging studies—primarily positron emission tomography (PET) and magnetic resonance imaging—investigating the pathogenic role of gut microbiota alterations in AD. More specifically, we summarized findings of structural changes of gut microbiota dysbiosis–related AD in brain regions such as hippocampal, white matter integrity loss, and disrupted connectivity, whereas we summarized the PET imaging findings such as neuroinflammation and increased Aβ or tau pathology linked to microbiota-driven immune and metabolic signaling.