Application of diffusion tensor imaging analysis along perivascular spaces in evaluating glymphatic system function in type 2 diabetes mellitus

Background Type 2 diabetes mellitus (T2DM) is often accompanied by cognitive dysfunction, though its underlying mechanisms remain unclear. Impaired glymphatic system function may contribute to cognitive impairment. Herein, we aimed to evaluate glymphatic activity in patients with T2DM using diffusion tensor imaging analysis along perivascular spaces (DTI-ALPS) and to explore its mediating role between white matter hyperintensities (Fazekas score) and Montreal Cognitive Assessment (MoCA) scores. Methods Thirty-eight patients with T2DM and 54 age- and sex-matched healthy controls underwent 3.0 T magnetic resonance imaging (MRI) and MoCA testing. The DTI-ALPS index was derived from diffusion tensor imaging data. Clinical variables included demographics, disease duration, metabolic indicators, and the homeostatic model assessment of insulin resistance (HOMA-IR) index. Group differences were analyzed using ANCOVA, correlations were assessed using Pearson analysis, and mediation analysis was used to evaluate the role of the DTI-ALPS index between Fazekas score and MoCA. Results The DTI-ALPS index was significantly lower in patients with T2DM having cognitive impairment compared to both healthy controls and patients with T2DM without cognitive impairment ( p < 0.001). MoCA scores positively correlated with the DTI-ALPS index ( r = 0.860, p < 0.001), while HOMA-IR showed a negative correlation ( r = −0.326, p < 0.05). Longer disease duration and higher Fazekas scores were associated with reduced DTI-ALPS index ( p < 0.05). Mediation analysis indicated that the association between Fazekas score and MoCA was significantly and partially accounted for by the DTI-ALPS index in patients with T2DM (effect = −0.344, p < 0.05). Conclusion The DTI-ALPS index was strongly associated with cognitive performance in patients with T2DM. Mediation analysis suggests that this relationship may reflect a mechanism in which impaired glymphatic function mediates the impact of white matter lesions on cognitive decline.