From the article:

Systemic immune-inflammation index (SII) is a novel inflammatory marker based on the composition ratio of blood cell counts. In this study, we evaluated the association between the SII and cerebral small vessel disease (cSVD) in health check-up participants. We evaluated participants from our health check-up registry between 2006 and 2013. The SII was calculated using the following formula: SII = (platelet count × neutrophil count)/lymphocyte count. cSVD was assessed by considering white matter hyperintensity (WMH) volume, lacunes, and cerebral microbleeds (CMBs). A total of 3187 participants were assessed. In multivariable linear regression analysis, the SII was significantly related to WMH volume [β = 0.120, 95% confidence interval (CI) 0.050–0.189]. However, lacunes and CMBs showed no statistical significance with the SII. In the subgroup analysis by age, the SII was significantly associated with WMH volume only in participants aged ≥ 60 years (β = 0.225, 95% CI 0.068–0.381). In conclusion, a high SII was associated with cSVD. Since this association was more pronounced in WMH than in lacunes or CMBs, WMH might be closer to the inflammation-related pathological mechanisms.

Age-related changes in systemic inflammation:

Interestingly, the close association between the SII and WMH volume in our study was significant only in older participants aged ≥ 60 years. This might be related to the aging-related changes in the homeostatic maintenance of our body’s inflammation and immunity (e.g., inflammaging, immunosenescence, and homeostenosis)