They may involve gray matter such as cerebral cortex, deep nuclei and brainstem. In these locations, they involve selectively myelinated axons while sparing the neuronal bodies. The pathology of MS is highly variable and its clinical course unpredictable. Some patients have a few lesions that do not progress. In others, new crops of lesions or expansion of already existing ones develop with each exacerbation.
Some patients have a relentless progression, leading to extensive confluent demyelination.
Usually, these patients have plaques elsewhere in the brain or develop them later. These other plaques may be clinically silent, whereas the optic and spinal lesions always cause symptoms. Perivascular inflammation, in the acute phase, damages the blood-brain barrier. Unlike brain tumors, acute MS lesions cause little or no mass effect. However, a subacute onset of neurological symptoms with a single contrast-enhancing lesion may mimic a neoplasm.