Quantitative susceptibility mapping of paramagnetic rim lesions in early multiple sclerosis: A cross-sectional study of brain age and disability

Objective

Chronic inflammation in multiple sclerosis is associated with neurodegeneration and progressive functional decline. Quantitative susceptibility mapping (QSM) is an MRI technique that visualizes paramagnetic rim lesions (PRLs), which are indicative of chronic inflammation. In this cross-sectional study, we explored the prevalence of PRLs in multiple sclerosis and assessed their associations with clinical disability, tissue magnetic susceptibility, and brain age predictions.

Methods

All participants from the NOR-MS study with a 3T MRI T1-weighted magnetization-prepared rapid gradient echo and QSM were included (n = 42, mean age = 39.4 years, 59.5 % females, median disease duration = 0.1 years [IQR: 0.02–5.42]). The presence and characteristics of PRLs were evaluated by an experienced neuroradiologist. PRL and non-PRL susceptibility were categorized into separate groups through manual segmentation and voxel-wise analysis. We utilized a validated simple fully convolutional network and T1-weighted images to estimate brain age, and its derivative – brain age gap (BAG). Clinical disability was assessed using the Expanded Disability Status Scale (EDSS).

Results

PRLs were identified in 14.3 % (n = 6) of study participants, and correlated with EDSS (rho = 0.86, p = 0.03). The mean paramagnetic rim susceptibility was 25.6 ± 14.1 parts per billion and correlated with EDSS (rho = 0.93, p = 0.008). EDSS was significantly higher in the PRL-positive group (median EDSS 2.25 vs 1.5, p = 0.02). The PRL-positive group exhibited a mean 5.6-year higher BAG (p = 0.01) than the PRL-negative group.

Conclusion

PRLs were present in a significant subset of study participants with MS and were associated with greater disability and higher BAG.