Researchers at the Mayo Clinic and Cleveland Clinic have reversed the traditional understanding of how multiple sclerosis (MS) begins and travels in the brain.
The common view is that the disease starts in the center of the brain, in the white matter mostly found there, and then moves toward the outer layers, such as the cortex.
But this study, which is unique because it focused on the brain tissues of patients in the very early stages of MS, shows the opposite: that it moves from the outside in.
It begins in the "subarachnoid space," which surrounds the brain, cushions it and is filled with cerebrospinal fluid. From there it moves into the white matter. This animation shows how the two hypotheses differ.
The findings are also significant because they support the hypothesis that inflammation, not neurodegeneration, is a main driver of the disease. The authors conclude that it is "overwhelmingly likely" that MS is fundamentally an inflammatory disease, and not a neurodegenerative disease similar to Alzheimer's.
Researchers are not entirely sure exactly causes MS, but the prevailing theory is that it is an autoimmune disease in which the body's own immune system attacks and destroys its own myelin, a fatty substance essential to the nervous system. It protects the crucial nerve fibers enable different sections of the brain to communicate.
When myelin is damaged (as in MS), messages between the brain and the body are delayed or blocked, leading to MS symptoms such as blindness, numbness, paralysis, and thinking and memory difficulties.
"Our study shows the cortex is involved early in MS and may even be the initial target of disease," co-lead author of the study and Mayo Clinic neurologist Dr. Claudia F. Lucchinetti told MedicalXpress. "Inflammation in the cortex must be considered when investigating the causes and progression of MS", she says. She and her co-author, Dr. Richard Ransohoff of the Cleveland Clinic, published the results of their study in the New England Journal of Medicine.
You can watch Dr. Lucchinetti explaining more about the study here:
photo: Myelinated neuron. The myelin is represented by the concentric circles around the axon surrounding the neuron. (Electron Microscopy Facility at Trinity College)