The MRI and MS: Part I: The Basics
As anyone who has MS knows, magnetic resonance imaging (MRIs) of the brain and spinal cord area frequent part of the life of an MS patient. The MRI provides an amazing window of detail into the structure and function of the brain and spinal cord. Although I never practiced medicine prior to the invention of MRIs, I can imagine how difficult it must have been.
As the name implies, the MRI is essentially a giant magnet that gives doctors an amazing view into the structure of the central nervous system. The brain is composed of neurons on the outside of the brain, termed the gray matter. The cables that connect neurons, called axons, form the inner part of the brain, and this is called the white matter. In some MRI sequences, the white matter looks white and the gray matter looks gray. In other sequences, this pattern is reversed. By administrating a contrast agent called gadolinium, areas of active inflammation can be detected. Doctors are able to view the brain from multiple different angles using MRIs. It is important to note, that unlike CT scans, MRIs are not associated with radiation. So unless a person has an allergy to the contrast agent or a metallic implant in their body, MRI scans are entirely safe.
The MRI is an extraordinarily powerful piece of technology. Its ability to allow us to see the brain is comparable in my opinion to a dermatologist using a magnifying glass to conduct a skin exam. In many cases something abnormal will be found, even in completely healthy people. In MS, studies have shown that for every clinical event a patient experiences, the MRI will show five to 10 as many lesions (these are also referred to as plaques). Usually, by the time a patient is diagnosed with MS, the MRI of the brain shows numerous lesions indicating the patient likely had the illness for several years prior to experiencing any clinical symptoms. Although it is technically possible for patients with MS to have a normal MRI, it is extraordinarily rare.
Most of the lesions on the MRI can be likened to scars on the skin: they represent areas of old injury. Although they can regress somewhat over time, often once a lesion is present it rarely goes away entirely. As with an old scar, this does not mean that it is causing any active symptoms for the patient. In contrast, some lesions appear bright with the administration of contrast. These lesions can be compared to active, bleeding wounds. They are more common in the earlier stages of the disease, and are often the radiographic correlate of a clinical relapse. Prevention of lesions on the MRI is a major focus of medications in clinical trials, though the degree to which lesions seen on MRI correlate with a patient’s clinical outcome is controversial.
In future posts I will cover the appearance of the MRI in MS and how neurologists use the MRI to treat patients.
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