National Multiple Sclerosis Society
June 9, 2000
Summary: An international team of researchers has reported results of a study of nervous tissue samples taken from people experiencing active MS symptoms:
Background: MS involves an immune-system attack against the insulating myelin coating of nerve fibers in the brain and spinal cord. The attack can strip myelin from the nerve fiber and leave a scarred lesion, or "plaque," that can be seen on MRI scans. The clinical course and symptoms of MS within and between individuals can be extremely variable, as is its effects on nervous tissue, as seen by MRI and other scanning methods. In addition, people with MS differ in their responses to therapy. Based on these and other observations, some investigators have suggested that MS may not be one single disease but a "syndrome" including a number of very similar diseases that all result in myelin destruction. These are among the reasons the investigators undertook a study looking at the physical appearance of actual MS lesions and the immune forces at work in the lesions.
The Study: The researchers examined nervous tissue samples taken from people experiencing active neurological symptoms. The samples came from 51 individuals who had brain biopsies (a rare procedure sometimes necessary to exclude other possible diseases) and from 32 individuals who had died in the midst of MS flare-ups, or relapses. Most of the individuals sampled were in fairly early stages of disease.
The team analyzed lesions in the brain tissues to determine what type of immune cells and proteins were present, where and to what extent myelin was lost, whether specific myelin proteins were absent or present, and whether myelin-making cells (oligodendrocytes) appeared to be damaged or dead.
The investigators were able to classify lesions into four different patterns of myelin destruction. Patterns I and II were similar, but not identical, in the types of immune activity present, in the absence of all myelin proteins, in the location of lesions near blood vessels, and in the presence of oligodendrocytes in the center of lesions. Pattern III had similar immune activity but lesions were not surrounding blood vessels, all but one type of myelin protein were still present in damaged myelin, and there were no oligodendrocytes left in the center of the lesions. Pattern IV, the most rare, showed immune activity in the lesion, but myelin loss was associated with oligodendrocyte death in a rim of adjacent, normal-appearing tissue, with almost a complete loss of oligodendrocytes in active and inactive lesion areas.
Patterns of lesions were different between individuals, but for a given indivdidual, multiple lesions had the same pattern. A distinct association between lesion type and the clinical form of MS was not clear. Pattern I and II lesions were found in people with all different clinical forms of MS. However, pattern III lesions were mainly found in individuals who had had the disease less than two months and pattern IV was found in only three individuals, all of whom had the primary-progressive form of MS.
What the Study Means: These findings suggest, but do not prove, that processes that lead to myelin destruction in MS may be different in distinct subgroups of the disease. This raises the possibility that there may be different causes for each subgroup, and also suggests that a therapy that may be effective in individuals with one subgroup of disease may be ineffective, or even be harmful, in individuals of a different subgroup.
Further research is required to confirm these results in a larger number of tissue samples and to find non-invasive ways to detect what type of myelin destruction any individual is experiencing, focusing on magnetic resonance imaging techniques to understand if MRI characteristics match the actual lesion pathology seen in tissues, and if both can be more closely associated with clinical disease type.
To follow up on this important work, the National MS Society just launched "The MS Lesion Project," a special Society-targeted investigation and the largest study of its kind to correlate clinical manifestations of MS and findings from MRI and brain tissue samples. The five-year, $1.8 million international collaborative research project is being conducted by Dr. Claudia Lucchinetti at the Mayo Clinic and the other collaborators in the current study.
From: Research Programs Department