Neuromyelitis optica (NMO) is an incurable, rare inflammatory disease of the central nervous system (CNS) that primarily affects the optic nerves, spinal cord and brainstem. Individuals with NMO may develop optic neuritis, which causes pain in the eye and vision loss, and transverse myelitis, which causes weakness, numbness, and sometimes paralysis of the arms and legs, along with sensory disturbances and loss of bladder and bowel control. NMO leads to loss of myelin, which is a fatty substance that surrounds nerve fibers and helps nerve signals move from cell to cell. It can also damage nerve fibers and leave areas of broken-down tissue. In the disease process of NMO, for reasons that aren’t yet clear, immune system cells and antibodies attack and destroy myelin cells in the optic nerves, spinal cord and brainstem.
The Difference Between NMO and MS
Multiple Sclerosis or MS is a fairly well known disease throughout the world. Many people know about it. However what many people don’t know is that Neuromyelitis Optica or NMO is another disease that is so similar to MS that it is often times misdiagnosed as such. But despite its outward appearance, NMO is actually not like MS at all. This is where the red flags come up. It’s critical to understand the difference and be diagnosed correctly in order to have the best outcome because the treatments for MS and NMO are completely different. MS treatment uses immune modulator medications whereas NMO utilizes immunosuppressant chemotherapy.
NMO is actually different than MS in one factor. The cells that attack the nerves, or more specifically the myelin sheath. Let me explain what the myelin sheath is. The myelin sheath is essentially a booster for your nerve impulses. They allow the nerve impulse to basically “jump” from node to node (gaps
between the myelin sheath), which speeds up the process. However, these myelinated neurons do not always regenerate. So if you have a disease like MS or NMO, your “speed boosters” for your nerve impulses are usually gone forever if attacked. This brings us to the cells that do the attacking. These cells are actually the cells that protect you by killing any pathogens (“disease carrying” cells) that enter your body. These cells that are supposed to be protecting your body against diseases, have a “glitch” and are now attacking the neurons. This is why those who have NMO or MS must take immunosuppressant and/or immunomodulatory therapy. Because in order to stop the cells from attacking the myelin sheath, the immune system must be shut down or at least reduced.
There are two main cells that guard your body against invaders. Well three, but the important ones for now are B-cells and T-cells. T-cells attack the Myelin sheath in MS. B-cells on the other hand attack the myelin sheath in NMO. What’s the difference? Well, Im sure you’ve heard of antigens or at least antibodies. Antigens are on the surface of cells and tell the body if they are what we call “self” or “nonself”. Antibodies are what bind to these “nonself” antigens in order to destroy the foreign cells. And what makes these antibodies? B-cells! And these are what attack the Myelin sheath in NMO. However in NMO, the myelin sheath is not the only thing under attack. The primary target for the B-cells is actually aquaporin. Aquaporin 4 to be exact. Yes, another scientific word. These are basically water channels. They are channels in the cell membrane that allow large amounts of water through, intead of the basic diffusion. But what about MS? Do T-cells destroy the myelin sheath in MS by using antibodies like NMO? No, they don’t. Only B-cells can make antibodies. So T-cells must use a different approach in MS. This is called the cell-mediated response. Instead of antibodies attacking the myelin sheath, in MS the T-cell itself must attack the myelin sheath, hence the term cell-mediated.
So to sum things up, NMO is attacked by B-cells and MS is attacked by T-cells. Almost. There’s one little thing more. B-cells and T-cells have a way of “talking” to each other and in some cases, B-cells require some help
from T-cells to help make antibodies. This doesn’t mean that T-cells make antibodies – only B-cells can do that – but they give a little help. So although the main player is the B-cell (and of course the antibodies) in NMO, the T-cell can also be called upon and so is therefore a part of the equation.
Overall, NMO and MS both attack the nervous system; however the means by which they do it are not the same. This is why MS and NMO must be treated differently. MS is treated with immune modulator medications and NMO is treated with immunosuppressant chemotherapy.