Magnetization Transfer and Diffusion Tensor Magnetic Resonance Imaging

Abstract

Patients with primary progressive (PP) multiple sclerosis (MS) represent a subgroup with clinical and magnetic resonance (MR) imaging (MRI) characteristics which differ from those of patients with relapsing-remitting (RR) MS or secondary progressive (SP) MS [1,2]. Although they experience a progressive disease course from onset, the burden and activity of lesions on their T2-weighted and gadolinium-enhanced brain MRI scans are, on average, lower than those seen in other MS phenotypes [3–8]. That the pathology of lesions in PPMS is characterized by a predominant loss of myelin and axons with only mild inflammatory components [9] can explain, at least partially, the relative paucity of conventional MRI-detectable activity [4, 5]. However, unlike the case of other disease phenotypes, in PPMS patients the correlation between MRI abnormalities and clinical disease severity is not significantly ameliorated in relation to the load of brain T1-hypointense lesions [7,8], which are thought to reflect areas where severe tissue disruption has occurred [10]. Two factors might explain the discrepancy between brain MRI and clinical findings in PPMS: first, the presence of diffuse tissue damage at a microscopic level [11], and, second, a prevalent involvement of the cervical cord [6,7], which might also explain the disproportion between the severity of locomotor disability and the less pronounced impairment of other functional systems [1].