MRI mimics of multiple sclerosis

Abstract

Diagnosis of multiple sclerosis (MS) is based on the demonstration of dissemination of lesions in space (DIS) and in time (DIT), as well as on the exclusion of an alternative neurologic disorder. As a paraclinical tool brain and/or spinal cord magnetic resonance imaging (MRI), showing typical lesion morphology, characteristic distribution of lesions, or involvement or specific anatomic structures, can support the diagnosis of MS. But from an imaging perspective a considerable amount of inherited and acquired disorders may manifest with radiologic evidence of DIT, DIS, or both. Hypoxic-ischemic vasculopathy, specially small-vessel disease, inflammatory disorders, vasculitis, and non-MS idiopathic inflammatory disorders, as well as some toxic, metabolic, and infectious disorders, may present mimicking MS on MR examinations and should be included in the differential diagnosis of MS-like lesions. Careful evaluation of associated findings on MRI, the so-called MRI red flags, such as the presence of infarcts, microbleeds, meningeal enhancement, and calcifications among others, are very helpful in suggesting a diagnosis other than MS. Complement MRI findings to patient’s history, demographics, and serologic findings are crucial to achieve the correct diagnosis. We will review the most frequent radiologic appearance and differential features from the most frequent MS mimickers.

Introduction

Magnetic resonance imaging (MRI) is highly sensitive for the detection of intracranial and spinal cord abnormalities, including the white-matter damage seen as hyperintense lesions on T2-weighted (T2WI) and fluid attenuated inversion recovery (FLAIR) images in patients with multiple sclerosis (MS). Although, in many cases, the characteristic lesion morphology, the patterns of distribution of lesions, or the involvement of specific anatomic structures can support the diagnosis of MS, it is important to bear in mind that many other disorders can present with a similar MRI appearance to MS, especially on T2WI/FLAIR images.

In a patient with symptoms suggestive of inflammatory demyelinating disease, the principal clinical objective is to exclude alterative non-demyelinating disorders and to distinguish MS from other idiopathic inflammatory demyelinating disorders. Together with a patient’s clinical history, examination, and laboratory findings, the MRI plays an important role in the exclusion of these alternative diagnoses. In this regard, the most common difficulty, by far, is to distinguish MS from acquired hypoxic/ischemic small-vessel disease (SVD) on the basis of its MRI appearance, especially in middle-aged or elderly patients. This is due to the high prevalence of SVD leukoencephalopathy in these age groups. Therefore, the first goal of this chapter is to emphasize those MRI features, which can be used to distinguish MS from hypoxic SVD. We will also discuss other less frequent acquired and inherited pathologic disorders that may affect white matter in a pattern similar to MS, both reviewing their most important imaging findings and identifying those MRI features which can be used to distinguish these diseases from MS. Advanced imaging techniques and high field strength (3 T) or ultra-high field strength (7 T) imaging may help to narrow the differential diagnosis but, because they are not routinely performed, we will focus on the use of conventional MRI sequences in the differential diagnosis of MS. Finally we will summarize those MRI findings which, if present, should suggest a diagnosis other than MS.