Subjective cognitive decline (SCD) is a risk factor for dementia. However, multiple pathologies, including amyloid deposition, cerebrovascular pathology, and depression, contribute to the heterogeneity in SCD. We included 170 non-demented elderly with 2-years follow-up to examine brain structural abnormalities in SCD. We found progressive and stable SCD individuals differed in deep white matter hyperintensities and temporoparietal grey matter atrophy. We used multi-model brain and behavioural factors to predict cognitive impairment and dementia progression. Periventricular white matter hyperintensities mediated the effect of amyloid accumulation on cognitive decline and disease severity, while depressive symptoms directly predicted disease severity.