Harrison DM, Shiee N, Bazin PL, Newsome SD, Ratchford JN, Pham D, Calabresi PA, Reich DS. Tract-specific quantitative MRI better correlates with disability than conventional MRI in multiple sclerosis. J Neurol. 2012 Aug 12. [Epub ahead of print]
Although diffusion tensor imaging (DTI) and the magnetization transfer ratio (MTR) have been extensively studied in multiple sclerosis (MS), it is still unclear if they are more effective biomarkers of disability than conventional MRI. MRI scans were performed on 117 participants with MS in addition to 26 healthy volunteers. Mean values were obtained for DTI indices and MTR for supratentorial brain and three white matter tracts of interest. DTI and MTR values were tested for correlations with measures of atrophy and lesion volume and were compared with these more conventional indices for prediction of disability. All DTI and MTR values correlated to an equivalent degree with lesion volume and cerebral volume fraction (CVF). Thalamic volumes correlated with all indices in the optic radiations and with mean and perpendicular diffusivity in the corpus callosum. Nested model regression analysis demonstrated that, compared with CVF, DTI indices in the optic radiations were more strongly correlated with Expanded Disability Status Scale and were also more strongly correlated than both CVF and lesion volume with low-contrast visual acuity. Abnormalities in DTI and MTR are equivalently linked with brain atrophy and inflammatory lesion burden, suggesting that for practical purposes they are markers of multiple aspects of MS pathology. Our findings that some DTI and MTR indices are more strongly linked with disability than conventional MRI measures justifies their potential use as targeted, functional system-specific clinical trial outcomes in MS.
We were aware that conventional MRI are not good measures of disability: some people with “clean scans” have got a lot of clinical symptoms, whereas some people who look and feel quite well show a lot of subclinical activity in their MRI scans. In clinical practise, we use more the comparison between two scans of the same person than an isolated scan. The exception is when there is Gad enhancement, which we understand as active inflammatory lesions that damage blood-brain barrier integrity. Unfortunately, DTI and MTR are not used in clinical practise because they take longer to acquire and make the procedure more expensive. We will need to get more information from clinical trials before putting pressure in health providers to make it available.