Discussion, Part II

Abstract

Dr. ARNOLD: To assess neuroprotection, it's important to be able to measure changes in myelin. Magnetization transfer ratio (MTR) imaging is a very sensitive method for measuring both myelin injury and myelin repair on a voxel-by-voxel basis, which can be used for evaluating this aspect of neuroprotection. Dr. ZIVADINOV: Are the data you've presented here only for original gadolinium-enhancing lesions or for all lesions that appear? Dr. ARNOLD: These data are strictly the percentage of the initial gadolinium-enhancing lesion volume. It's effectively the percentage of the voxels that were gadolinium enhancing on the original scan that show these changes over time. That's a very important point, because it's what gives MTR its power: you can do this for all the lesions. Atrophy is an important measure of neuroprotection, so touching on the atrophy data thus far is relevant. The conventional MRI data that exist show that the rate of atrophy in patients can be related to the frequency of contrast-enhancing lesions. In the Richert group study, patients who had no contrast-enhancing lesions had very low rates of atrophy over the subsequent 5 years, whereas those with more than three contrast-enhancing lesions had much higher rates of atrophy over the subsequent 5 years. This implies that there is some dependence of atrophy on focal inflammation, which you might think obvious, but as Gary [Birnbaum] said earlier, there's a tendency now to attribute the loss of brain volume to diffuse degenerative processes that don't necessarily involve the lesions. My group was interested in this dependency of atrophy on the lesions, in part for the reasons I just hinted at and in part because of the phenomenon of T2 lesion volume plateauing and even decreasing over time in patients with MS. I tried to get our investigators to look at lesion formation and …