EXPRESS: Consistency of associations of systolic and diastolic blood pressure with white matter hyperintensities: a meta-analysis.

BACKGROUND: White matter hyperintensities (WMH) are the commonest manifestation of cerebral small vessel disease, associated with stroke, functional impairment and cognitive decline. They are commonly preceded by hypertension, but the magnitude and clinical importance of this association is unclear. AIMS: Quantify the relationship between blood pressure and white matter hyperintensities across studies Methods: PubMed and EMBASE were searched for studies reporting associations between concurrent or historic blood pressure and WMH. Beta coefficients from linear models were extracted, whether standardised, unstandardised, unadjusted or adjusted for age, sex and cardiovascular risk factors. Beta-coefficients were combined by fixed and random effects meta-analysis, combining standardised beta-coefficients or unstandardised coefficients measured by consistent methods. RESULTS: 24 of 3,230 papers were eligible, including 50,999 participants. Systolic blood pressure was significantly associated with WMH volume after maximal adjustment (standardised beta 0.096, 95%CI 0.06-0.133, p<0.001, I2=65%), including for concurrent readings (b=0.106, p<0.001) or readings 5 years previously (b=0.077, p<0.001), and for younger or older populations (mean age <65: b=0.114; >65 b=0.069). Unstandardised, adjusted associations were similar for raw WMHV, log-transformed WMHV or WMHV as percentage of intracranial volume. Unadjusted associations with SBP were greater (standardised beta=0.273, 0.262-0.284, p<0.0001). However, whilst associations with DBP were weaker than SBP (standardised beta=0.065, p<0.001), they were minimally affected by adjustment for age. CONCLUSIONS: A standard deviation increase in SBP is associated with 10% of a standard deviation increase in WMHV, providing the current best estimate of the potential reduction in progression of WMH expected with good control of blood pressure.