Paramagnetic Rim Lesions: Broad MS Diagnostic Criteria Update

Paramagnetic rim lesions, or PRLs, are now part of the diagnostic toolbox for MS and they speed up diagnosis in real-world settings. In 2024, the McDonald criteria formally incorporated PRLs as a confirmatory signal in certain scenarios, alongside central vein sign and optic nerve lesions, with the goal of enabling a single-visit diagnosis. The data show specificity around 90-98% and sensitivity roughly 36-86%, depending on cohort and threshold used. UB researchers helped validate these lesions and supported their use in clinics to shorten time to diagnosis.

The details are typically found in methodology or footnotes. The practical upshot: chronic active white matter lesions can be identified by their iron-laden edge, seen as a dark ring on susceptibility-weighted imaging.

High-resolution 3T sequences like SWAN (Susceptibility-weighted angiography network; a high-resolution MRI sequence highlighting iron content) or 3D EPI with phase maps and T2-FLAIR overlays are used in routine practice, and radiologists classify PRLs into three categories. Definite PRLs show a full, closed ring with circumferential hypointensity; probable PRLs have an incomplete ring or edge-centered signal; possible PRLs are low-confidence features whose inclusion reduces specificity.

Thresholds and clinical decision-making for PRLs

Thresholds drive decision-making. A threshold of ≥1 PRL yields about 90% specificity (95% CI 0.77-0.97) and 86% sensitivity (95% CI 0.71-0.95 in multicenter early MS cohorts, n=78). In retrospective cohorts with larger samples (n=574, 473 MS), ≥1 PRL increases specificity to 98% while sensitivity drops to 36%. There is a move to ≥2 PRLs to boost specificity in early disease, though sensitivity varies by study. The clinical takeaway: PRLs add confidence in the right patients, especially early, but they cannot stand alone.

Prevalence data show PRLs in about 46% of early MS suspects, with a median of 3 lesions per patient (range 1-9). Importantly, 89% of PRL-positive cases meet the 2017 McDonald criteria, showing PRLs align imaging with established diagnostic frameworks. These figures come from consensus panels with MAGNIMS, CMSC, and NAIMS, coordinated by UB’s Buffalo Neuroimaging Analysis Center.

Historical context and updates to diagnostic criteria

Historically, pre-2024 PRLs were markers of smoldering inflammation but not diagnostic. The 2024 McDonald update, reported in Lancet Neurology, elevates PRLs to a confirmatory role in specific scenarios and adds CVS and optic nerve lesions as complementary signals.

The rationale is to reduce misdiagnosis, which can reach up to 20% with nonspecific MRI findings. In practice, PRLs and CVS together support MS dissemination in space without prior attacks, and this shift matters for patient management.

2025 data and ongoing validation

Across 2025, post-2024 data reinforced the move. At ECTRIMS in September 2025, a multicenter Australian study found PRLs useful for faster recogjition within the 2024 criteria, confirming PRLs as chronic active lesion biomarkers. The MSAA report in November 2025 echoed that emphasis, highlighting early detection gains. UB’s December 2025 updates are notable: Michael G. Dwyer, PhD, BNAC, and NAIMS steering member, co-authored a Lancet Neurology consensus with MAGNIMS/CMSC/NAIMS, describing PRLs as highly specific to MS and indicative of ongoing brain damage, rare in mimics. A PubMed Brain study (Oxford University Press, 2025) with 574 participants (473 MS, 53 non-inflammatory, 48 other inflammatory) found that definite/probable PRLs yielded 98% specificity.

The Cleveland Clinic and other centers publish online reports supporting clinical utility of PRLs at first presentation. Practically, clinics should implement clearer criteria, improve interrater reliability for definite/probable PRLs, and adopt protocols compatible with 3T scanners without long, specialized sequences. In UB terms, BNAC experience supports implementing PRLs into diagnostic workflows, with staff trained to recognize ring morphology and apply threshold rules consistently.

What this means for practice or research programs

What does this mean for practice or research programs? First, adopt high-resolution 3T imaging protocols that support SWAN or equivalent phase-based sequences, with T2-FLAIR overlays. Second, train readers on the three PRL categories and the diagnostic thresholds, noting that a single PRL can tilt the MS diagnosis in a compatible clinical picture. Third, use PRLs with CVS and lesion load data, but avoid over-reliance on any single biomarker. Fourth, stay current with evolving consensus statements from MAGNIMS, CMSC, NAIMS, and major societies, since literature shifts toward earlier and more confident single-visit diagnoses.

The real-world impact depends on accessibility and workflow. This means streamlined imaging protocols, prompt reporting, and clear communication with patients about what a PRL means for prognosis and treatment planning. The details are usually tucked away in the methodology (but practical effects are evident).

Public engagement and implementation questions

What do you think? Will PRLs become the default in early MS workups, or remain one tool among several? If you’re implementing this in your clinic, share how you handle thresholds, reader training, and integration with existing McDonald criteria workflows. Comment with your experiences. If you want more, see UB’s recent statements and the Lancet Neurology consensus, which lay out the current stance and rationale behind these shifts.

Sara Morgan

Dr. Sara Morgan takes a close, critical look at recent developments in psychology and mental health, using her background as a psychologist. She used to work in academia, and now she digs into official data, calling out inconsistencies, missing info, and flawed methods—especially when they seem designed to prop up the mainstream psychological narrative. She is noted for her facility with words and her ability to “translate” complex psychological concepts and data into ideas we can all understand. It is common to see her pull evidence to systematically dismantle weak arguments and expose the reality behind the misconceptions.