Neuroimaging: Evaluating the clinical course and pathology of MS

Conventional magnetic resonance imaging (MRI) techniques are important tools in the diagnosis and management of patients with multiple sclerosis (MS), but they reveal only a small part of the overall disease process. Lesion burden on T2-weighted MRI correlates to some extent with disability during the early stages of the disease, but is less sensitive to increasing disability among patients with more advanced disease. New approaches are required to assess neurodegenerative changes that occur at even the earliest stages of MS but become the predominant pathophysiology in the progressive stages of MS. Diffusion tensor imaging (DTI) is an MRI technique that allows quantification of tissue water molecules that are restricted in their direction of motion by central nervous system (CNS) whitematter tracts. DTI provides several measures that can be used to assess the integrity of axons and myelin, and these DTI indices correlate significantly with histologic measures of CNS injury. Magnetization transfer imaging provides a relatively specific measure of lipid-associated macromolecules, and is therefore sensitive to changes in myelin, perhaps before typical lesions appear on conventional MRI. Optical coherence tomography (OCT) uses infrared light to calculate the thickness of the retinal nerve fiber layer, which consists of axons that form the optic nerve. Several studies have demonstrated that OCT is able to visualize and quantify neurodegeneration in patients with MS. New imaging technologies may provide opportunities to examine neurodegeneration in patients with MS and to assess the neuroprotective effects of new MS therapies.