The role of advanced magnetic resonance imaging techniques in primary progressive MS.

Primary progressive multiple sclerosis (PPMS) is characterized by a steady progression of irreversible disability from the onset of the disease. Although magnetic resonance imaging (MRI) is a valuable tool to quantify the disease burden in the brain and spinal cord of patients with MS, measures derived from conventional MRI, including T2-visible lesions, gadolinium-enhancing lesions and atrophy, are correlated only weakly with the clinical manifestations of PPMS. On the contrary, advanced MRI techniques are contributing significantly to the understanding of the mechanisms underlying the irreversible accumulation of disability in PPMS patients. Data from quantitative MRI studies suggest that the extent and topography of "diffuse" damage in different central nervous system (CNS) compartments (i.e. normal-appearing brain white matter and grey matter and the spinal cord) is associated with the severity of disability in PPMS and can predict subsequent medium-term disease evolution. Functional MRI studies have shown that the impairment of the adaptive capacity of the cortex to limit the clinical consequences of structural CNS damage is yet another factor contributing to the manifestations of this condition.