Diffusion tensor imaging in multiple sclerosis: Correlations with clinical disability

Introduction. Diffusion measurements inside biological tissues provide information about tissue configuration at a microscopic level, which are inaccessible to other magnetic resonance (MR) techniques. Objectives. To quantify, using diffusion tensor imaging (DTI), the damage of lesions and normal-appearing white matter (NAWM) from patients with multiple sclerosis (MS) and to investigate the magnitude of the correlation between DTI metrics and clinical disability. Methods. Conventional MR and DTI scans were obtained from 78 patients and 20 controls. After creating mean diffusivity (D) and fractional anisotropy (FA) maps, D and FA values were measured for 4846 lesions (3207 non-enhancing T1-isointense, 1511 nonenhancing T1-hypointense, and 128 enhancing), 497 NAWM areas from patients and 160 WM areas from controls. Results. The average lesion D was higher and the average lesion FA was lower than the corresponding quantities of the NAWM (P<0.001). The D̄ values of the enhancing and non-enhancing lesions were not different, whilst enhancing lesions had lower FA (P<0.001). T1-hypointense lesions had higher D̄ and lower FA than T1-isointense lesions (p<0.001). NAWM of patients had higher D and lower FA than WM of controls (P=0.01). In all patients, a moderate correlation was found between lesion D̄ and the EDSS score (r=0.3, P=0.01). The magnitude of this correlation was greater (r=0.5) when secondary progressive (SP) MS patients, whose disability was also significantly correlated with average lesion FA (r=-0.5, P=0.03) were considered in isolation. Conclusions. This study shows that DTI is able to identify MS lesions with severe tissue damage and to detect changes in the NAWM. It also indicates that DTI measures are correlated with clinical disability, especially in patients with SPMS, suggesting a role for DTI in the monitoring of the advanced phases of the disease.