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IS THERE A LESION FOR EVERY SYMPTOM?
It seems that one of the most difficult questions on the forum is "What relationship there is between lesions actually seen on the MRI's and the symptoms that one has?" Can you reliably see a lesion for every symptom? Is there a symptom or can you find an abnormality on the physical exam for every lesion that is seen? The answer is an unqualified, "NO." Too many doctors, neurologists and people try to draw conclusions about this. It may be one of the greatest pitfalls in using MRIs to diagnose Multiple Sclerosis.
First, lets talk about the BRAIN. Remember that about 90% or so of our brains are "unused." That means that we don't know what those areas do when they are healthy or might do if they are damaged. ALL of the scientific articles are clear that the majority of MS lesions in the brain are not "eloquent", that is, they don't "speak up" with actions or sensations in the body. The same is true that those areas don't show symptoms if they are damaged. No good MS Specialist is going to try to map all the lesions with the symptoms that are showing up in the patient. It is almost impossible and it is a waste of time. It is well documented that some people with many, severe symptoms may have very few visible lesions. And some people who are diagnosed when they have just one symptom may have a whole brain full of lesions on their first MRI which had never before "spoken up."
Many lesions in MS are still invisible. All good MS doc's will tell you that they believe that many brain lesions are still invisible to the MRI. The National MS Society site states that 5% of people with MS have "normal" MRIs. If they are invisible, then of course they can't be used to diagnose MS. But, also a negative MRI does not completely rule out MS in a person with a history and physical findings that suggest the disease. My own MS Neurologist say something very interesting when I developed severe facial pain. In MS this would be caused by a lesion in a specific place. He looked at my newest MRI and said,"Well, I don't see a lesion that's causing your face pain. That's good! You don't want a big lesion in your brainstem!" By saying this he was indicating two things. The first is that he knew I had a lesion, but it was invisible. The second was that he believed me when I said I had pain, even though there was no proof on the MRI.
Now, some lesions can be big enough and in known active areas so that we can recognize that those lesions are causing a specific symptom. But this is the exception, not the rule.
MS "tends" to cause lesions within a characteristic pattern in the brain. But this just means that, when you look at a large number of people with MS and plot all of their lesions, the majority of lesions will fall into this pattern. This pattern is generally symmetrical side to side, but not a perfect mirror-image. Any one person or any person with just a few lesions may have them occur in any white matter location. . Even people with a "characteristic pattern of lesions" will have some that don't fall into the perfect "zones." Please reread those last two sentences.
The more the lesions follow the common pattern, the easier the job of the neurologist, and the easier the diagnosis. It's those people with suggestive symptoms and suggestive abnormalities on physical exam but WHO HAVE NO LESIONS, VERY FEW LESIONS, OR LESIONS IN LESS USUAL PLACES that will have a tougher time with the diagnosis (if they have MS). Too many people are told that their lesions "aren't in the right place so they don't have MS." Or they are told that they don't have enough lesions, so they do not have MS." In reality they shouldn't have been told they don't possibly have MS. They should be told that the MRI is inconclusive. In this case the neurologist, if he suspected MS before the MRI, should continue to suspect it after the MRI and do more extensive testing. Also, plans should be made to repeat the neuro exam and the MRI at intervals like every 6 months or at some interval or if the patient develops more symptoms.
The point to take home: Most lesions seen in the MRI of the brain do not correlate well with the problems the patient has. A good doctor will not try to tell you different. And you shouldn't spin your wheels trying to look up mapping of the brain - unless that is something you would do anyway for giggles.
THE BRAINSTEM AND SPINE
The nerves in the brainstem and spine are all "eloquent" to some extent. They drive the functions and the movement of the body and they relay information like sensations from the body back to the brain. A small area of damaged myelin in the spine is "more likely" to cause a direct symptom or problem. Spinal lesions are a little less common than brain lesions, but more directly connected (in an obvious way) to our disease. But, also many spinal lesions are still invisible. One of the reasons for them being invisible is that they are harder to get good clear MRI images on. This appears to be one of the strengths of the newer generation of MRI machines. They have a higher magnet strength and because of this they have a higher resolution. They can see smaller lesions. The strongest MRI machines currently in clinical use today use a 3 Tesla magnet. Tesla is the "unit of measurement" of magnets, like "amps" is the unit of measurement of an amplifier. Older MRI machines, which are by far the most common in use, may use a magnet that is 1.5Tesla or weaker. Much stronger magnet MRI machines are being developed, but currently are used only in research.
Lesions in the brainstem and spine are stronger evidence for the presence of MS than are lesions in the brain. This is because there are many disorders that cause brain lesions, but many fewer that cause lesions in the spinal cord or the brainstem. And even though there tends to be a better correlation between symptoms or abnormal physical findings and lesions here, it is still often hard to draw connections between all of them.
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