The MRI and MS Part IV: Following Progress of MS
No one disputes the importance of MRI in diagnosing MS and detecting active inflammation. Once the diagnosis of MS has been made, however, the role of the MRI is somewhat less clear, at least in patients who are clinically stable. Most neurologists order MRIs of the brain on a periodic basis, every 6 to 12 months, to see if new lesions are developing in the absence of clinical symptoms. If patients are experiencing significant changes on their MRIs, many doctors will use this as a reason to change therapies rather than wait until a patient experiences a clinical relapse.
This practice is somewhat controversial, however, as the MRI is far from a perfect indicator of how a patient is doing. I have seen many patients whose MRIs reveal numerous lesions, but they feel fine and their neurological exams are nearly normal. Similarly, I have seen patients with minimal changes on their MRI who are not doing as well. In the MS field, this is referred to as the “clinical-radiographic paradox.” Nonetheless, it is probably the case that patients who develop multiple new lesions on their MRIs in a short period of time—even in the absence of clinical symptoms—are in danger of having a relapse and clinical disability and should have their treatment regimen reconsidered.
Probably the strongest correlation between how a patient is doing clinically and their MRI is not the number of lesions they have or the number of active lesions, but rather the volume of brain tissue where both the axons and the myelin have been destroyed. These areas appear as dark holes on the MRI and are appropriately labeled “black-holes.” These may take years to develop and are often not evident in newly diagnosed patients. When I do see them, it is further evidence that a patient, even if he is newly diagnosed, has likely had the disease for many years without clinical symptoms. In the MRI at left, the red arrows point to areas of permanently destroyed brain tissue.
Additionally, this destructive process in MS can manifest itself by generalized atrophy. At right is a brain with significant enlargement of the ventricles and overall atrophy of the brain. Most likely, this manifests itself as cognitive impairment rather than some focal neurological symptom. Although sophisticated measures can show evidence of brain atrophy in early MS, it usually becomes obvious only after many years of severe illness. Even then, it is not obvious in all patients.
Finally, patients who have been on Tysabri for over 18 months and who have evidence of prior exposure to the JC virus that causes brain infection progressive multifocal leukoencephalopathy (PML) may have MRIs on a frequent basis (every 3 to 6 months) with the hopes that PML can be detected via radiographic means before it presents clinically. This is not always easy, however, as the early radiographic manifestations of PML can look nearly identical to the lesions in MS. Nonetheless, for patients on Tysabri, frequent monitoring with MRIs is essential.
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