Pathology

Areas of demyelination occur as plaques and the appearance varies slightly according to the evolution of the lesion. In the fixed brain they are grey in colour and usually well demarcated from the surrounding white matter. Acute plaques are surrounded by a rim of oedema and may be less well-defined. The optic nerves are commonly involved and may appear to be shrunken. Within the cerebral hemispheres plaques are particularly marked around the lateral ventricles and they are commonly seen within the spinal cord. No area is exempt and they may also involve the grey matter. Sometimes they are found incidentally in the brains of individuals with no clinical history of the disease. They are usually detectable radiologically using MRI scans. Using modern scanning techniques plaques can be identified in almost all cases with clinical evidence of the disease. It is important to realise that the radiological appearances alone are not diagnostic and that similar appearance can be seen in a variety of other diseases.

Cerebrospinal fluid may show a variety of immunological and inflammatory abnormalities. There may be an increased number of lymphocytes and histiocytes (phagocytic cells) in the active stage of the disease, and the protein level is usually elevated with a raised IgG level, which after electrophoresis is seen to consist of oligoclonal bands. This is also not specific and may be found in other disorders with an immune component. Diagnosis, therefore, depends upon a strong clinical suspicion together with relevant radiological and laboratory abnormalities.

Figures 1-3 illustrate the macroscopical and microscopical appearances of multiple sclerosis.

This figure is a horizontal slice of a brain from a patient with multiple sclerosis. The loss of myelin has resulted in asymmetrical distortion of the shape of the ventricles. Plaques of demyelination appear as grey areas within the white matter, particularly around the angles of the ventricles.

Figure 2 is a section of brain stained for myelin (blue). The plaques of demyelination appear as well-demarcated pale areas with a central blood vessel.

Figure 3 is a longitudinal section of optic nerve from a patient with multiple sclerosis. The pale area to the left is demyelinated and there is sharp demarcation from the myelinated area to the right.