Do MRIs Paint an Accurate Picture?
Ah, MRIs! We all know them well! Some of us get a good nap in despite the jackhammering noises swirling around our heads, while others have to fight the urge to crawl out of the tube and run for the hills. They are the best test we have to diagnose MS, track disease progression, and evaluate the effectiveness of treatment, but they are still an imperfect tool (though, if you have lived with MS for a while, you probably already knew that!). They can often raise more questions than they answer, which often begs the question - what exactly is the role of MRI scans in MS?
Matching the story and the picture
MRI scans come into play the second someone goes to their doctor with any sort of neurological symptom that could be MS. They are absolutely crucial in diagnosing MS, but from that point on, their use can be an inexact science. Often the story and the picture don’t match up, a situation dubbed the “clinico-radiological paradox”. Either the MRI shows several lesions but the person isn’t having any correlating symptoms, or the person is having new symptoms, but no new disease activity is seen on the MRI scan. Needless to say, this is pretty frustrating for all parties involved!
What causes this clinico-radiological paradox?
There are a few proposed reasons for this paradox. First and foremost, we know that our current technology misses things and is not 100% accurate. For instance we don’t have a good way to image grey matter, and we are now learning that damage to the grey matter in the cortex plays a big role in disease progression. New symptoms could also be due to lesions accumulating in the spinal cord and not the brain. Traditionally, it has been thought that disease activity in the brain correlates to disease activity in the spinal cord, but more and more we are seeing that the two areas behave independently. Therefore, we probably need to be doing MRIs of the spinal cord more often. And lastly, when we see new lesions but the person isn’t having any symptoms, it could be because the damage occurred in an area of the brain that compensates quickly and easily. The brain is masterful at compensating for damage, which can spare people from having symptoms with new lesions.
When new symptoms occur
I mentioned that disease activity in the brain and the spinal cord don’t necessarily go hand-in-hand, so how do we know what area to image when new symptoms occur? This is where clinicians have to put on their detective hats! A new lesion in the spinal cord is going to affect the areas of the body below the level of damage. For instance, numbness or weakness in the arms is going to come from the cervical spine, but something in the legs like foot drop could really arise from any point in the spinal cord. The brain is a bit easier to correlate because we know which areas of the brain control different tasks:
Why the neurological exam is also a key player
Therefore, if someone is having a new symptom, usually their neurologist has a pretty good idea of what areas are being affected, even if the MRI does not show new lesions. I think it’s important to note that MS isn’t the only disease where there is a discrepancy between symptoms and test findings. Even in the simplest of conditions, like an ear infection, we have to put symptoms, test results, and clinical findings all together to reach a diagnosis and treatment plan. While the MRI is the most valuable test we have to measure MS, the neurological exam is equally important in making treatment decisions and tracking disease progression.
The past, present and future of MRI technology
In the past decade, MRI technology has come a long way. We can now diagnose MS much more easily and quickly, instead of having to wait around for someone to have a second relapse. This means that people can start treatment sooner, and hopefully will translate into better long term outcomes.
Even though we are lucky to have better technology, there is still a lot of room for improvement. Many people have access to 3-tesla MRIs which are faster and more accurate than 1.5T machines, and research labs have even started using 7T MRIs. Better technology will ideally help us see the effect of MS on the brain’s grey matter, eliminate the clinico-radiological paradox, predict how a person is going to do long-term based on their MRI findings, and clearly evaluate whether a treatment is working or not. This technology is on the horizon, and I think it is going to help us greatly!
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