New research shows the brain and spinal cord scars in people with multiple sclerosis may offer clues to why they develop progressive disability but those with related diseases where the immune system attacks the central nervous system do not. In a new study, Mayo Clinic researchers and colleagues assessed if inflammation leads to permanent scarring in multiple sclerosis; aquaporin-4 antibody positive neuromyelitis optica spectrum disorder; and myelin oligodendrocyte glycoprotein antibody associated disorder. They also studied whether scarring may be a reason for the absence of slow progressive disability in AQP4-NMOSD and MOGAD, compared with MS.

In all three of these diseases, the body's immune system targets the myelin. This causes inflammation and leads to removal of myelin within the brain and spinal cord. Visual problems, numbness, weakness, or bowel or bladder dysfunction are common symptoms. Areas of demyelination appear as white spots on an MRI. The repair mechanisms within the body try to reinsulate the nerves and repair the lesions, but this may be incomplete, leading to a scar that remains visible on future MRIs. Just like an electrical cable without its insulation, this scar may leave nerve fibers vulnerable to further damage and to degenerate over time.

The study included 156 patients, consisting of 67 patients with MS; AQP4-NMOSD, 51; and MOGAD, 38. These patients had 172 attacks, or relapses, combined.

With MS, the researchers found that areas of inflammation reduced only modestly in size and led to a moderately sized scar. When scars are in regions of the brain and spinal cord that control arm and leg muscles, nerve fibers can degenerate and lead to slow worsening of disability in the secondary progressive course of MS.

But AQP4-NMOSD and MOGAD are different from MS in that they do not have the same slow worsening of disability typical of the progressive course in MS. With AQP4-NMOSD, large areas of inflammation occur during attacks, which often results in severe symptoms. Scars are common, but they tend to be smaller and in less important locations than in MS. Thus, less long-term problems result from those scars. With MOGAD, despite having large areas of inflammation during an attack, the researchers found lesions tended to disappear completely over time and not leave any scar. This fits well with the excellent recovery from episodes and overall good long-term prognosis without the slow worsening disability seen in MS.

The reasons behind this recovery are not clear, the researchers note. It may suggest an enhanced ability to put the covering back onto nerves, or remyelination.

The study was published in the journal Neurology.