Neuroradiology

Multiple sclerosis

(MS), the most common and most widespread acquired demyelinating disease whose aetiology is as yet unknown and whose treatment is disappointing. It is also probably the most extensively studied, at least from the clinical point of view, particularly since MR has provided the most powerful tool for studying and monitoring the number, location, size, characteristics and development of the demyelinating plaques. Despite a probably unique aetiology, many different clinical and morphological variants are observed.

Among them are the classical form of MS, called Charcot's disease, neuromyelitis optica or Devics syndrome, concentric sclerosis or Balo concentric sclerosis, and diffuse sclerosis or Schilders disease.

The Charcot form may be further subdivided into four main groups, according to clinical presentation and evolution:

1. Relapsingremitting, in which patients experience a relapsingremitting course of exacerbations and remissions of multifocal neurological deficits. The disease progresses for decades and usually patients are not severely neurologically impaired within the first ten years

2. Chronic progressive, in which the disease has almost a continously progressive course, without remissions and subsequent relapses. Patients exhibiting the chronic progressive pattern typically have more severe spinal cord involvement.

3. Secondary progressive, in which after an initial relapsingremitting course of at least six months, a chronic progressive evolution takes place.

4. Benign, in which no significant neurological impairment is seen ten years after onset of the disease.

Although most patients initially present in the third and fourth decades, 15% come to attention before the age of 20 and 10% after 50 years of age. Females are slightly more commonly affected.

The first clinical symptom is often impaired or double vision, due either to optic neuritis or to involvement of oculomotion in the brain stem. Patients may complain of weakness, numbness, tingling, and gait disturbances. As the disease progresses, loss of sphincter control, blindness, paralysis and dementia may develop.

Although the precise aetiology is still unknown, there is, however, a general consensus that MS is most likely to be an autoimmune demyelinating disorder triggered by an exogenous factor acting on an inherited susceptibility.

Most probably a virus acts as an immunogenic agent on peptides from myelin basic protein induced T-cell receptor genes on CD4+ cells.

Pathologically pinkgrey areas of oedematous myelin are seen in the acute phase while atrophy and cystic changes are seen in the chronic stage. Histologically inflammatory perivascular changes around the venules of the white matter with macrophage infiltration are found in the acute phase. Astrogliosis is found in silent chronic plaques.

Imaging

MR has changed the diagnostic process in MS. CT was frequently normal, and positive only in case of large plaques or enhancing plaques. Double doses of contrast, with delayed scan, had been advocated to increase sensitivity.

MR has a much higher sensitivity, at probably around 85%, exceeding that of all other tests including evoked potentials and oligoclonal bands.

Most MS plaques, iso- or hypointense on T1-weighted images, are markedly hyperintense on T2-weighted images (Fig.1). They usually have a characteristic ovoid shape, from medial to lateral, and are mainly close to the periventricular white matter. However, any sort of variation is possible, from small subcortical punctate lesions to very large, tumour-like plaques involving a large part of the centrum semiovale (Fig.2), to confluent periventricular and peritrigonal plaques.

Some plaques enhance in their entirety v matter abnormalities.

GS

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Fig.1

a, b, c. MR, T2-weighted axial images. Multiple foci of hyperintensity are seen in the white matter of the corona radiata, periventricular white matter and subcortical white matter. Some of the lesions are confluent, particularly in the peritrigonal area; others are isolated and have a perivenular location. d, e, f. Axial T1-weighted MR images following gadolinium injection. Some of the lesion enhance, with different patterns (homogeneous, ring-like). The patient has definite multiple sclerosis.
Multiple sclerosis, Fig.1 (a)
Multiple sclerosis, Fig.1 (b)
Multiple sclerosis, Fig.1 (c)
Multiple sclerosis, Fig.1 (d)
Multiple sclerosis, Fig.1 (e)
Multiple sclerosis, Fig.1 (f)
Multiple sclerosis, Fig.2 (a)
Multiple sclerosis, Fig.2 (b)