Cerebral microbleeds (CMB) are small, round, focal haemorrhages visible on T2*-weighted gradient-recalled echo (GRE) or susceptibility-weighted imaging (SWI) sequences on magnetic resonance imaging (MRI). Pathologically, CMB are commonly associated with small vessel arteriosclerosis (typically in the setting of hypertension) and/or cerebral amyloid angiopathy (CAA), and the location of CMB has been traditionally used to predict the underlying aetiology (Greenberg et al., 2009). In healthy older adults, the prevalence of CMB has been estimated to range between 5-15% and they have been shown to be associated with an increased risk of cognitive impairment and dementia (Akoudad et al., 2016, Charidimou et al., 2018, Koennecke, 2006, Romero et al., 2017). A previous meta-analysis of 15 MRI studies in 2016 reported that CMB were present in approximately 24% of people with AD, although the prevalence estimates were noted to be highly influenced by the MRI technique and field strength (Sepehry et al., 2016). Compared to AD, CMB have been relatively under-investigated in other neurodegenerative dementias, such as dementia with Lewy bodies (DLB) and Parkinson’s disease dementia (PDD). One previous study reported significantly higher frequency of CMB in DLB (45%) compared to PDD (26%) and healthy controls (17%), with a lobar predominance observed (Kim et al., 2015). The pathophysiology and clinical relevance of CMB in people with Lewy body dementias (DLB/PDD) remain to be elucidated.

In this study, we aimed to estimate the pooled prevalence of CMB across the three most common dementia diagnoses in older people, i.e. AD, DLB and PDD, using meta-analytic methods. The regional characteristics of CMB and associations with vascular risk factors and amyloid-β burden were also examined in these dementia subtypes.