A meta-analysis of 20 studies and 4,786 patients with multiple sclerosis estimated how common slowly expanding lesions are, and how far they overlap with paramagnetic rim lesions. Both are markers of chronic active inflammation, but they are identified differently — slowly expanding lesions by concentric growth on serial conventional MRI, paramagnetic rim lesions by a rim on susceptibility-sensitive sequences.
Slowly expanding lesions accounted for 14% of all T2 lesions, and 78% of patients had at least one. Mean per-patient volume was 1.42 mL against 10.6 mL of total T2 lesion. Only 11% of slowly expanding lesions overlapped with paramagnetic rim lesions.
That last number is the useful one. The two markers are routinely discussed as though they identify the same biology; on these data they largely do not. The proportion of lesions that were slowly expanding was similar in relapsing-remitting and progressive disease at around 15%, though more progressive patients had at least one. Heterogeneity was high across every analysis with no source identified, so treat the point estimates as approximate.
- 78% of patients had at least one slowly expanding lesion — this is not a rare finding
- Only 11% overlap with paramagnetic rim lesions; they are not interchangeable markers
- Requires serial MRI with consistent technique, which limits routine applicability
- Similar lesion proportions in relapsing and progressive disease
- High unexplained heterogeneity; the intervals are wide for a reason
The statistics, in plain English
The intervals here are wide — 10 to 21% for the lesion proportion, 6 to 20% for the overlap — because between-study heterogeneity was high and no source for it was found. When that happens the pooled estimate is best read as a rough central value rather than a precise one, and differences of a few percentage points between subgroups should not be interpreted.
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