Lessons from magnetic resonance imaging in multiple sclerosis.

Magnetic resonance imaging is a potent diagnostic tool in multiple sclerosis: it can reveal dissemination of lesions in both space and time in many patients with isolated neurological syndromes. Many more new lesions occur than clinical relapses. A consistent very early event is the breakdown of the blood-brain barrier which is largely repaired over weeks, leading to marked changes in the size of acute lesions. Chronic lesions show persistent oedema and enlarge through cycles of renewed peripheral activity. The vascular changes reflect inflammation: the resulting MRI changes provide, for the first time, a non-invasive means of monitoring disease activity and its modification by treatment.