Multiple Sclerosis (MS)

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Diagnosis Definition

MS is defined histopathologically as inflammatory demyelination in the central nervous system (CNS); the etiology is unknown
The age of onset is usually between 15-50 (average age 34) with a 2:1 female predominance
MS is most commonly relapsing-remitting (i.e., clearly defined relapses with no disease progression between them)

Imaging Findings

The “McDonald diagnostic criteria” includes dissemination of lesions in both space (one or more hyperintense lesions on T2-weighted imaging in two of the following areas: periventricular, juxtacortical, infratentorial, and spinal cord) and time (new T2 hyperintense lesion on follow-up MRI or simultaneous presence of enhancing and nonenhancing lesions on a single MRI)
Lesions are usually ovoid, well demarcated, and oriented perpendicular to the margins of the lateral ventricles
Nodular and peripheral enhancement of lesions on post-contrast T1-weighted images, or diffusion restriction, indicates active demyelination
Tumefactive demyelination can present as larger masslike lesions

Pearls

Serial MRI examinations are used to monitor disease course and guide clinical management, including changes in therapy
Initial periventricular lesions may be linear (aka, “Dawson fingers”), distinguishing MS from other white matter disorders
T2-weighted non-FLAIR images are often superior to FLAIR images for showing infratentorial (posterior fossa) lesions
Incomplete peripheral lesion enhancement (aka, “open ring” sign) can distinguish demyelination from other processes
The mass effect and edema associated with tumefactive demyelination is disproportionately less than expected for the size of the lesion, helping to differentiate it from neoplasm
Perfusion weighted MR images show tumefactive demyelinating lesions to have low perfusion whereas high grade astrocytomas are hyperperfused

References

Vigeveno RM, Wiebenga OT, Wattjes MP, et al. Shifting imaging targets in multiple sclerosis: from inflammation to neurodegeneration. J Magn Reson Imaging 2012; 36(1):1-19
Polman CH, Reingold SC, Banwell B, et al. Diagnostic criteria for multiple sclerosis: 2010 Revisions to the McDonald Criteria. Ann Neurol 2011; 69:292-302

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