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Multiple sclerosis (MS) is a relatively common acquired chronic demyelinating disease involving the central nervous system, and is the second most common cause of neurological impairment in young adults, after trauma 19. Characteristically, and by definition, multiple sclerosis is disseminated in space (i.e. multiple lesions in different regions of the brain) and in time (i.e. lesions occur at different times).
A number of clinical variants are recognized, each with specific imaging findings and clinical presentation. They include:
classic multiple sclerosis (Charcot type)
This article concerns itself primarily with classic (Charcot type) multiple sclerosis. The other variants are discussed separately.
Importantly, neuromyelitis optica spectrum disorder (Devic disease) was considered a variant of multiple sclerosis, but is now recognized as a distinct entity, and is therefore also discussed separately.
The presentation is usually between adolescence and the sixth decade, with a peak at approximately 35 years of age 12,19. There is a strong, well recognized female predilection with a F:M ratio of approximately 2:1 19.
Multiple sclerosis has a fascinating geographic distribution: it is rarely found in equatorial regions (e.g. 15 per 100,000), with incidence gradually increasing with distance from the equator (e.g. 250 per 100,000) 12,19.
a strong association with HLA-DR15 (formerly covered by HLA-DR2) class II has been identified 11
Melkersson-Rosenthal syndrome: postulated
Clinical presentation is both highly variable acutely, as a result of varying plaque location, as well as over time. Examples of common clinical features include 23,24:
brainstem and cranial nerve involvement:
cerebrum and spinal cord involvement:
limb sensory loss or paresthesias
upper motor neuron signs
A number of patterns of longitudinal disease have been described 11,12:
most common (70% of cases)
patients exhibit periodic symptoms with complete recovery (early on)
secondary progressive (SPMS)
approximately 85% of patients with relapsing-remitting MS eventually enter a secondary progressive phase
primary progressive (PPMS)
uncommon (10% of cases)
defined by a progressive accumulation of disability for >12 months from disease onset, which can be determined prospectively or retrospectively
patients do not have remissions, with neurological deterioration being relentless
incorporates the previously described "progressive-relapsing" phenotype
benign multiple sclerosis
15-50% of cases
defined as patients who remain functionally active for over 15 years, and thus is only a retrospective diagnosis
As is evident from this list, there is overlap, and in some cases, patients can drift from one pattern to another (e.g. relapsing-remitting to secondary progressive).
Upon presentation patients often have evidence of multiple previous asymptomatic lesions, and the diagnosis of multiple sclerosis can be strongly inferred. In other instances patients present with the first plaque. This is known as clinically isolated syndrome (CIS) and not all patients go on to develop multiple sclerosis.
Radiologically isolated syndrome (RIS) is another entity based on MRI brain findings which described as incidental white matter lesions suggestive of MS on imaging in a patient without associated clinical symptoms 17.
The diagnosis of multiple sclerosis requires the constellation of clinical findings and various investigations (see McDonald diagnostic criteria for multiple sclerosis), including 19:
oligoclonal bands in CSF
immunoglobulin G in serum
abnormal visual evoked potential
lack of viable alternative diagnosis
The exact etiology is poorly known although it is believed to have both genetic and acquired contributory components. An infectious agent (e.g. EBV), or at least a catalyst, has long been suspected due to the geographic distribution and presence of clusters of cases; however, no agent has yet been firmly confirmed. Some authors also suggested that "chronic cerebrospinal venous insufficiency" can cause or exacerbate MS but this theory has not been proven by further investigations 15.
Multiple sclerosis is believed to result from a cell-mediated autoimmune response against one's own myelin components, with loss of oligodendrocytes, with little or no axonal degeneration in the acute phase; however, in later stages, loss of oligodendrocytes results in axonal degeneration.
Demyelination occurs in discrete perivenular foci, termed plaques, which range in size from a few millimeters to a few centimeters 19.
Each lesion goes through three pathological stages:
early acute stage (active plaques)
active myelin breakdown
plaques appear pink and swollen
plaques become paler in color ("chalky")
chronic stage (inactive plaques/gliosis)
little or no myelin breakdown
gliosis with associated volume loss
Plaques can occur anywhere in the central nervous system. They are typically ovoid in shape and perivenular in distribution.
CT features are usually non-specific, and significant change may be seen on MRI with an essentially normal CT scan. Features that may be present include:
plaques can be homogeneously hypoattenuating 8,11
brain atrophy may be evident in long-standing chronic MS 5
some plaques may show contrast enhancement in the active phase 7,11
MRI has revolutionised the diagnosis and surveillance of patients with MS. Not only can an MRI confirm the diagnosis (see McDonald diagnostic criteria for multiple sclerosis), but follow-up scans can assess response to treatment and help determine the disease pattern.
Although many sequences are contributory, the 2018 Revised Guidelines of the Consortium of MS Centers MRI Protocol for the Diagnosis and Follow-up of MS plaques lists the following core sequences 25:
FLAIR (axial and sagittal)
ideally performed as a 3D volumetric scan (1 mm isotropic), or
3 mm contiguous
T1: 3D inversion recovery prepared gradient echo
T2 (axial): 3D or 2D
NB: contrast is not necessary for routine asymptomatic follow-up.
lesions are typically hyperintense
acute lesions often have surrounding edema
central vein sign: at higher field strengths most plaques have been shown to be perivenular (at 3 T, 45% of lesions; at 7 T, 87% of lesions) 19
lesions are typically hyperintense
a very early sign is called ependymal dot-dash sign 16
when these propagate centrifugally along the medullary venules and are arranged perpendicular to the lateral ventricles in a triangular configuration (extending radially outward - best seen on parasagittal images), they are termed Dawson's fingers
FLAIR is more sensitive than T2 in the detection of juxtacortical and periventricular plaques, while T2 is more sensitive to infratentorial lesions
T1 C+ (Gd)
active lesions show enhancement
enhancement is often incomplete around the periphery (open ring sign)
active plaques may demonstrate high or low ADC (increased or decreased diffusion) 10,11,22
also typically open ring in morphology
PD images are better at detecting cervical spinal cord MS lesions especially when T2W images fail to demonstrate these lesions 26
double inversion recovery (DIR)
a sequence that suppresses both CSF and white matter signal and offers better delineation of the plaques
Location of the plaques can be infratentorial, in the deep white matter, periventricular, juxtacortical or mixed white matter-grey matter lesions.
Even on a single scan, some features are helpful in predicting relapsing-remitting vs progressive disease. Features favoring progressive disease include:
large numerous plaques
hyperintense T1 lesions
Treatment and prognosis
The aim of treatment is twofold: to curtail progression (disease-modifying agents) and symptomatic relief.
Steroids, disease-modifying therapies, and autologous hematopoietic stem cell transplantation are all used. Although discussion of individual agents and therapies is well beyond the scope of this article, it is worth being aware of the main agents available and their mechanism of action 20:
interferon beta: inhibition of T-lymphocyte proliferation
glatiramer acetate (Copaxone): immunomodulation
teriflunomide (Aubagio): reduces both T-cell and B-cell activation and proliferation
dimethyl fumarate (Tecfidera) and diroximel fumarate (Vumerity): immunomodulation
fingolimod (Gilenya), siponimod (Mayzent) and ozanimod (Zeposia): prevents lymphocyte migration out of lymph nodes and into CNS
natalizumab (Tysabri): inhibits binding of lymphocytes to endothelium
cladribine (Mavenclad): purine analog that targets lymphocytes
ocrelizumab (Ocrevus) and ofatumumab (Kesimpta): anti-CD20 monoclonal antibodies
alemtuzumab (Lemtrada): immunomodulation of T-cell and B-cell function
mitoxantrone (Novantrone): reduces T-cell and B-cell proliferation and reduces T-cell activation
Prognosis is variable and depends on the pattern of disease a patient has (e.g. primary progressive carries a worse prognosis than relapsing-remitting).
In general, patients with relapsing-remitting MS will progress to secondary progressive disease in 10 years and will require ambulatory aids (e.g. cane/wheelchair/frame) in another 5 to 15 years 12. Approximately half of the affected individuals will no longer be independently ambulatory after 20 years 19.
Overall life expectancy is also reduced, by 7 to 14 years 19.
In addition to the potential for disease progression resulting in progressive neurological impairment, a number of specific complications need to be considered. These include 20,21:
particularly in patients treated with natalizumab with positive JC virus serology
a complication of cessation of natalizumab or treatment for natalizumab-related PML with plasma exchange or immunoabsorption 21
rarely lymphoma appears to arise from previously identified demyelinating lesions
>2-times increased risk of stroke 28, possibly related to chronic inflammatory vasculopathy
History and etymology
Multiple sclerosis was first defined by Jean-Martin Charcot (1825-1893), French neurologist, in 1868 27.
The differential diagnosis is dependent on the location and appearance of demyelination. For classic (Charcot type) MS, the differential can be divided into intracranial and spinal involvement.
For intracranial disease, the differential includes almost all other demyelinating diseases, as well as:
CNS fungal infection (e.g. Cryptococcus neoformans): patients tend to be immunocompromised
Marchiafava-Bignami disease (for callosal lesions)
CNS manifestations of primary antiphospholipid syndrome 13
For spinal involvement, the following should be considered:
Multiple sclerosis variants (e.g. tumefactive MS) are discussed separately.