Several studies have reported reduced water diffusion in acute inflammatory-demyelinating lesions in multiple sclerosis (MS) on brain MRI.1–4 Spinal cord (SC) MRI represents an important part of diagnostic examinations in MS as 80% to 90% of patients with MS show focal and/or diffuse signal abnormalities. Acute SC lesions frequently show contrast enhancement because of an increased vascular permeability. We report 2 patients with acute relapses who showed symptomatic SC lesions with reduced diffusion.
Over the past year I have wondered whether MRI research in MS has stagnated? The turn of phrase 'beating a dead horse' comes to mind (however, unpalatable that may sound). An alternative (more positive analogy) might be 'I hate to drive this nail into the wall', but some lateral thinking may help (wink)? Precisely what is needed is anyone's guess; but a starting point might be to seek out ideas in the most unlikeliest corners of research publications - other scientific areas, low impact but well reviewed articles, abstracts from past conferences...
The authors here discuss a form of imaging which has been around for many years but only used in stroke. I've been vegetating about acute MS lesions in the spinal cord for some time now, particularly because our radiology colleagues commonly interpret these changes as a stroke and not MS activity (the authors touch on this but don't have an answer for this). Moreover, since it's a lottery as to whether there is a contrast enhancement of lesions or not, adding diffusion weighted imaging to our protocol may increase likelihood of assigning an individual as demonstrating active disease than previously.
What is diffusion-weighted imaging (DWI)? DWI uses the diffusion of water molecules in tissues to generate contrast in images. In tissues which demonstrate cellular swelling, and hence reduced water mobility, there is high signal demonstrated from stationary water molecules on DWI maps referred to as "restricted diffusion".
The authors suggest that in the very early phase of MS lesion development where contrast enhancement may be absent, restriction is present (see figure above). They consider this to be a transient phenomenon, present for a few days before pseudonormalization (although I think this may be variable from lesion to lesion from personal experience). Equally, it's uncertain whether all lesions go through this step-wise process or only a sub-set of them demonstrate this phenomenon.