The presence of a paramagnetic phase rim in multiple sclerosis is linked to lesion age: An exploratory study.

Background: In relapsing-remitting multiple sclerosis (RRMS), smouldering inflammation at the rims of chronic active lesions is increasingly recognised as a key driver of disease progression. Paramagnetic rim lesions (PRLs), detected using susceptibility-weighted imaging, have emerged as a potential biomarker of this chronic inflammatory activity. However, their clinical relevance and relationship to lesion-specific features such as size and age remain poorly understood.

Objective: To investigate the association between PRL presence and clinical/radiological measures of disease progression, and to explore how PRLs relate to lesion size and age.

Methods: A retrospective study of 60 RRMS patients with over 5 years of magnetic resonance imaging data was conducted using susceptibility-weighted angiography. Lesions larger than 100 mm³ were analysed.

Results: PRLs were present in 48% of patients and represented 13% of lesions. PRLs were significantly larger and more structurally damaged, with volume correlating with EDSS change and brain atrophy. All lesions formed within 5 years of imaging were PRLs. This finding was validated in two independent international cohorts. Moreover, the proportion of rim-positive lesions decreased as lesion age increased.

Conclusion: PRLs are closely linked to lesion age and early development, supporting their role as a dynamic biomarker of lesion activity in multiple sclerosis.