The role of magnetic resonance imaging in the study of multiple sclerosis: diagnosis, prognosis and understanding disease pathophysiology.

Magnetic resonance imaging (MRI) has become an established tool to diagnose multiple sclerosis (MS) and to monitor its evolution. In patients at presentation with clinically isolated syndromes suggestive of MS, MRI criteria for MS diagnosis have been proposed and are updated on a regular basis. In addition, MRI "red flags" useful for the differential diagnosis from other neurological conditions which can mimic MS have been identified. In patients with established MS, the ability of MR measures in explaining patients' clinical status and progression of disability is still suboptimal. This has prompted the extensive application of modern MR-based technologies to estimate the overall disease burden in patients at different stages of the disease. The use of these techniques has allowed to grade in vivo the heterogeneity of MS pathology not only in focal lesions, but also in the normal-appearing white matter and grey matter. Combined with the use of functional MRI, this is ameliorating progressively our understanding of the factors associated to MS evolution. This review summarizes how MRI has improved our ability to diagnose MS and to predict its course, as well as how it is changing our understanding of the factors associated with the accumulation of irreversible disability in this condition.