Quantification of subtle blood-brain barrier disruption in non-enhancing lesions in multiple sclerosis: a study of disease and lesion subtypes.

Few attempts have been made to detect subtle blood-brain barrier (BBB) leakage in visibly nonenhancing MRI lesions in multiple sclerosis (MS). For 19 patients, longitudinal relaxation time (T₁) maps were generated from MRI scans obtained before, and at 20, 40 and 60 minutes after injection of gadolinium (Gd)-DTPA (0.3 mmol/kg). Regions of interest (ROI) were placed around non-enhancing lesions, and in paired contralateral normal appearing brain tissue (NABT). Post-Gd rate of R₁ (=1/T₁) rise (ΔR₁/Δt), was used to quantify leakage. ΔR₁/Δt was greater in lesions than paired NABT (P⩽0.001 at all post-Gd timepoints). ΔR₁/Δt was greater in T₁ hypointense than isointense lesions (P=0.001 and 0.01 for first and second timepoints respectively), and negatively related to lesion cross sectional area (P⩽0.001 at all post-Gd timepoints). Relapsing remitting (RRMS) lesions had a greater initial ΔR₁/Δt than secondary progressive (SPMS) lesions (P=0.04), but this was not seen in subsequent timepoints. ΔR₁/Δt in visibly enhancing lesions was significantly greater than in visibly non-enhancing lesions, with no overlap in the normal ranges of the two populations. Subtle BBB leakage is a consistent feature in non-enhancing lesions, and is distinct from the overt BBB leakage observed in visibly enhancing lesions. It is detectable using quantitative contrast-enhanced MRI. It is apparent in all clinical and lesion subtypes studied, and greater in T₁ hypointense and smaller lesions. Larger initial ΔR₁/Δt in RRMS than SPMS lesions may reflect differences in blood volume rather than BBB leakage. [ABSTRACT FROM AUTHOR]