Magnetic resonance (MR) imaging as a marker for multiple sclerosis

Since the diagnosis of multiple sclerosis (MS) may not be clear on clinical grounds or from other paraclinical tests, and due to the necessary assessment of new pharmacological therapeutical agents which demand objective outcome parameters for relatively short trials, magnetic resonance imaging (MRI) is not only used to diagnose MS, but is also broadly used to monitor disease progression. In exploratory trials, where MRI is used as a primary outcome measure, serial scans are used to detect disease activity as the number of active lesions showing signal enhancement after gadolinium administration. When the result is positive, the drug has to be tested further in a phase III study, using clinical endpoints as primary outcome measurements. MRI can be used as a secondary outcome measure. Given the uncertain relation between MRI and clinical findings, MR findings provide only supportive evidence. Serial scans (usually yearly) are used to monitor disease progression as an increase in total lesion load. Consequently, reproducibility of the lesions and therefore spatial resolution, should be maximized. Several putative treatments have been assessed using MR monitoring in phase II and phase III trials. A multitude of phase II trials have shown that it is indeed possible to demonstrate that MR is capable of showing, even in small groups, whether new drugs have any effect on the development of lesions.