Clinical significance of diffusion tensor imaging in metachromatic leukodystrophy

Background and Purpose: Metachromatic leukodystrophy (MLD) is a lysosomal enzyme deficiency disorder leading to progressive demyelination and, consecutively, to cognitive and motor decline. Brain MRI can detect affected white matter as T2 hyperintense but cannot quantify the gradual microstructural process of demyelination more accurately. Our study aimed to investigate the value of routine MR diffusion tensor imaging in assessing disease progression. Materials and Methods: MR diffusion parameters (ADC and FA) were in the frontal white matter (FWM), central region (CR) and posterior limb of the internal capsule (PLIC) in 111 MR data sets from a natural history study of 83 patients (age 0.5-39.9 years; 35 late-infantile, 45 juvenile, 3 adult, with clinical diffusion sequences of different scanner manufacturers) as well as 120 controls. Results were correlated with clinical parameters reflecting motor and cognitive function. Results: ADC values increase and FA values decrease depending on disease stage/severity. They show region-specific correlations with clinical parameters of motor and cognitive symptoms, respectively. Higher ADC levels in CR at diagnosis predicted a disease course with more rapid motor deterioration in juvenile MLD patients. In highly-organised tissue like the corticospinal tract in particular, diffusion MR parameters were highly sensitive to MLD associated changes and did not correlate with the visual quantification of T2 hyperintensities. Conclusion: Our results show that diffusion MRI can deliver valuable, robust, clinically meaningful and easily obtainable/accessible/available parameters in the assessment of prognosis and progression of metachromatic leukodystrophy. Therefore, it provides additional quantifiable information to established methods such as T2 hyperintensity.