This section will use Multiple Sclerosis as a prototype for this group of disorders.

Slide 78 & Slide 79

Photographs 78 and 79 are coronal sections taken from the brains of patients who died with multiple sclerosis (MS). The lesions in these pictures are chronic inactive plaques. In MS a plaque is defined as a sharply defined area of demyelination. The disease is characterized by plaques anywhere within the central neuroaxis with however certain patterns of predilection. Predilection for periventricular regions is well shown in these 2 gross pictures. Plaques also tend to occur at grey/white cortical junctions. In the brain stem and spinal cord (where white matter is just below the pia) sub-pial plaques are common. The optic nerve, chiasm and tract are not only frequently involved but also clinically expressive. In MS there is a discrepitancy between the extent of plaque formation and clinical symptoms because many plaques are in areas which are not very clinically expressive, and because axons within plaques can conduct. Since myelin is present in grey as well as white matter, plaques also involve grey matter but not as extensively as central white.

Slide 80 & Slide 80a & Slide 80b

Now lets look at the microscopy. Slide 80 is a photomicrograph of a newly forming lesion. Shown here are perivascular leukocytes morphologically consistent with lymphocytes. Slides 80 a and b show very cellular active lesions. These are filled mainly with macrophage/microglia cells and lymphocytes. The latter are immunolabeled with a brown reaction product in 80b. In contrast older lesions are characterized by astrocytosis, complete loss of myelin. Picture 81 (below) is from the center of a chronic plaque it reveals a lesion with little cellularity composed of astrocytes. Myelin stained section of this lesion, slide 82 shows the complete loss of myelin, left side of image, which typlifies plaques. If we were looking at an axonal stain of this section we would see relative axonal preservation.

Slide 81 & Slide 82

For those of you who wish to read a little concerning the immunological aspects of MS, Click on additional text

For a brief discussion of other demyelinating diseases, Click on additional text.