Comparative analysis of glymphatic system alterations in multiple sclerosis and neuromyelitis optica spectrum disorder using MRI indices from diffusion tensor imaging

Abstract Objective The glymphatic system is a glial‐based perivascular network that promotes brain metabolic waste clearance. Glymphatic system dysfunction has been observed in both multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD), indicating the role of neuroinflammation in the glymphatic system. However, little is known about how the two diseases differently affect the human glymphatic system. The present study aims to evaluate the diffusion MRI‐based measures of the glymphatic system by contrasting MS and NMOSD. Methods This prospective study included 63 patients with NMOSD ( n = 21) and MS ( n = 42) who underwent DTI. The fractional volume of extracellular‐free water (FW) and an index of diffusion tensor imaging (DTI) along the perivascular space (DTI–ALPS) were used as indirect indicators of water diffusivity in the interstitial extracellular and perivenous spaces of white matter, respectively. Age and EDSS scores were adjusted. Results Using Bayesian hypothesis testing, we show that the present data substantially favor the null model of no differences between MS and NMOSD for the diffusion MRI‐based measures of the glymphatic system. The inclusion Bayes factor (BF 10 ) of model‐averaged probabilities of the group (MS, NMOSD) was 0.280 for FW and 0.236 for the ALPS index. Conclusion Together, these findings suggest that glymphatic alteration associated with MS and NMOSD might be similar and common as an eventual result, albeit the disease etiologies differ. Practitioner Points Previous literature indicates important glymphatic system alteration in MS and NMOSD. We explore the difference between MS and NMOSD using diffusion MRI‐based measures of the glymphatic system. We show support for the null hypothesis of no difference between MS and NMOSD. This suggests that glymphatic alteration associated with MS and NMOSD might be similar and common etiology.