Systemic immune-inflammation index and progression of white matter hyperintensities of presumed vascular origin. A longitudinal population study in community-dwelling older adults living in rural Ecuador

Background: Information on the association between the systemic immune-inflammation index (SII) and white matter hyperintensities (WMH) of presumed vascular origin is confined to cross-sectional studies. We sought to evaluate the impact of SII on WMH progression in community-dwelling older adults. Methods: Following a longitudinal prospective study design, participants of a population-based cohort received baseline blood tests to calculate the SII (platelets x neutrophils / lymphocytes x 10⁹ L) together with clinical interviews and brain MRIs. Participants with follow-up brain MRI were included in the analysis. Poisson regression models adjusted for demographics and cardiovascular risk factors were fitted to assess the incidence rate ratio of WMH progression by levels of the SII. Results: Across 246 study participants (mean age: 65.5 ± 5.9 years; 55% women), the mean SII was 434.7 ± 193.8 × 10⁹ L, and WMH progression was found in 101 (41%) individuals after a mean of 7.3 ± 1.5 years. A multivariate Poisson regression model showed increased WMH progression rate among individuals in the fourth quartile of the SII compared with those in the first quartile (IRR: 1.87; 95% C.I.: 1.02–3.41). Conclusions: Study results provided novel evidence of an independent association between the SII and WMH progression. The SII may be able to identify individuals at high risk of WMH progression.