Objective: To compare MS normal-appearing white matter (NAWM) where new gadolinium-enhancing (Gd+) lesions do and do not arise.
Methods: A total of 22 relapsing-remitting MS patients and 11 healthy control subjects completed as many as 12 monthly brain MRI sessions. Quantitative measures of gadolinium enhancement (GDR), water proton density (PDN), water proton T2 relaxation time constants (T2), magnetization transfer ratio (MTR), and T1-weighted signal intensity (T1N) were followed serially in healthy control and MS NAWM.
Results: A total of 129 new Gd+ lesions were identified in 11 patients. PDN, T2, MTR, and T1N were diffusely abnormal in MS NAWM. NAWM regions in which new Gd+ lesions arose have increased GDR, PDN, and T2, and reduced MTR and T1N compared with contralateral homologous NAWM regions in which no new Gd+ lesions arose. Differences between these NAWM regions preceded lesion appearance for at least several months. After lesions became visible, GDR returned to baseline within 2 months, and PDN and MTR had larger residual abnormalities than T2 or T1N.
Conclusions: Quantitative MRI measures are diffusely abnormal in MS NAWM. These measures are, on average, more abnormal in NAWM regions in which new Gd+ lesions arise. After the appearance of Gd+ lesions, measures of PDN and MTR may provide more appealing markers of relatively irreversible tissue damage than measures of T2 and T1N.