Longitudinal myelin MR imaging in patients with multiple sclerosis: a narrative review

Progression of multiple sclerosis (MS) remains incompletely understood. MS is characterized by demyelination, resulting in a wide variety of symptoms. Conventional magnetic resonance imaging (MRI) is the current standard for diagnosing and monitoring patients. However, conventional MRI has its limitations in visualizing the myelin dynamics. In contrast, advanced myelin-specific MRI techniques enable non-invasive, in vivo quantification of myelin content. Such approaches hold promises for the early detection of pathology and for improving the understanding of disease mechanisms and their relationship to clinical outcomes, particularly since many patients with MS experience progression of symptoms that cannot be fully explained by conventional imaging measures. This narrative literature review aims to summarize recent advances in longitudinal myelin-specific MRI studies in MS and their clinical applications. Overall, longitudinal studies demonstrated that myelin-specific MRI techniques can capture dynamic changes in myelin, possibly aiding in understanding the progression of MS, although inconsistencies persist both between and within techniques. Even though more myelin-sensitive than myelin-specific methods, such as diffusion MRI or multi-contrast methods, are not specific to demyelination, they could aid clinical follow-up by predicting lesion formation, as changes are visualized before being present on conventional MRI. These findings underscore the need for future research that integrates MRI-derived metrics with detailed assessment of disease courses.