The Impact of Sleep Disorders on Glymphatic Function in Parkinson's Disease Using Diffusion Tensor MRI

Hourly Variations in Glymphatic Function Based on MRI Scan Times in Cognitively Normal Individuals

RATIONALE AND OBJECTIVES

This study evaluated glymphatic function changes according to MRI scan time over a 24-hour cycle, using diffusion tensor image analysis along the perivascular space (DTI-ALPS) to assess interstitial fluid dynamics.

MATERIAL AND METHODS

This single-center retrospective cohort study included cognitively normal participants between January and August 2023. Participants were grouped by MRI scan time: dawn, early morning, daytime, and evening/night. Glymphatic function was assessed via the ALPS index calculated from DTI. ALPS index values were compared among groups using one-way ANOVA with post hoc pairwise independent t-tests. Multiple linear regression analysis adjusted for age, sex, and mini-mental state examination scores was used to compare daytime ALPS index with other groups. Paired t-tests assessed ALPS index changes in participants with follow-up MRIs.

RESULTS

Among 539 participants (age: 70 ± 10 years, 41.4% male), the dawn group had the highest mean ALPS index, followed by early morning, evening/night, and daytime groups (P =0.024). Daytime ALPS index was significantly lower than dawn (P =0.0036) and early morning (P =0.018). Multiple linear regression confirmed lower daytime ALPS index, with the dawn group showing the largest difference (0.067, 95% CI: 0.025-0.108; P =0.002). No significant difference was observed in ALPS index for follow-up scans from dawn or evening/night to daytime (P =0.353).

CONCLUSION

Glymphatic function varies diurnally, with lower values during daytime. These findings emphasize the importance of circadian timing in evaluating glymphatic function using DTI-ALPS. Further studies are needed to explore intra-individual glymphatic variations.