Synopsis

MR imaging has been established as the most important tool for diagnosing multiple sclerosis (MS). In addition, this modality is increasingly being used to monitor disease activity, disease progression and therapeutic effects, and is therefore now recognized as an “imaging biomarker” for MS. Furthermore, MR imaging is also useful for diagnosing the side effects of pharmacotherapies. This lecture focuses on the role of MR imaging in the diagnosis and management in MS.

The McDonald criteria are the most widely used diagnostic criteria for MS. The 2010 revision of these criteria is the most recent version, and represents simplification of the previous version¹. In these diagnostic criteria, MR imaging plays a crucial role in demonstrating dissemination of lesions in both space and time. Dissemination in space can be demonstrated as one or more T2 lesions in at least two of the following four regions; periventricular, juxtacortical, infratentorial and spinal cord¹. Dissemination in time can be demonstrated by: 1) a new T2 and/or gadolinium-enhancing lesion(s) on follow-up MR imaging, with reference to a baseline scan, irrespective of the time of the baseline MR imaging or 2) simultaneous presence of asymptomatic gadolinium-enhancing and nonenhancing lesions at any time¹.

In 2016, the European collaborative research network that studies MR imaging in MS (MAGNIMS) proposed modifications to MR imaging criteria for demonstrating dissemination in space as follows: dissemination in space can be shown by involvement of at least two of the following five areas: three or more periventricular lesions, one or more infratentorial lesion, one or more spinal cord lesion, one or more optic nerve lesion, and one or more cortical or juxtacortical lesion². This proposal may be adopted in the next version of the McDonald criteria.

To diagnose MS, exclusion of other demyelinating diseases, including neuromyelitis optica spectrum disorder (NMOSD) and acute demyelinating encephalomyelitis (ADEM) is also important. Characteristic MR findings in MS as opposed to NMOSD include periventricular ovoid lesions³ (Fig. 1), subcallosal striations⁴, isolated U-fiber lesions⁵ (juxtacortical lesion⁶) (Fig. 2), cortical lesions⁷ and peripheral spinal cord lesions⁸. On the other hand, lesions involving the corticospinal tracts, extensive hemispheric lesions, periependymal lesions, medullary (area postrema) lesions (Fig. 3), severe optic neuritis, longitudinally extensive spinal cord lesions preferentially involving the central gray matter would favor NMOSD^8-10. Criteria to distinguish a first attack of MS from ADEM (Fig. 4) include: 1) absence of diffuse bilateral lesion pattern, 2) presence of black holes (T1-hypointense lesions) and 3) presence of two or more periventricular lesions^{11, 12}.

MR imaging has also been recognized as a biomarker of MS¹³. One important role of a biomarker is in clinical trials, and monitoring treatment response in individual patients is another. Assessment of treatment response to disease-modifying drugs can help in the personalization and optimization of therapy for the individual patient¹⁴.

MR imaging is also important for the diagnosis of side effects caused by drugs. MS patients treated with disease-modifying drugs, such as natalizumab may develop progressive multifocal leukoencephalopathy (PML)¹⁵. MR imaging is useful for the early diagnosis of natalizumab-associated PML^16-18. MR features of early natalizumab-associated PML include mixed cortical and white matter lesions, unilobar lesions, focal lesions, punctate lesions, U-fiber lesions, hyperintense lesions on diffusion-weighted images^17,18. Comparison with previous MR examinations can improve specificity for natalizumab-associated PML¹⁸.

Acknowledgements

References

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