Rare, debilitating, but highly treatable, neuromyelitis optica syndrome disorders (mercifully better known by the acronym NMOSD) are a group of autoimmune conditions that mess with your central nervous system, the pathway by which your brain and the rest of your body send messages to each other. When your brain says, “Touch this!” and your hand sends back the information, “Ow, that’s hot!”, this is your central nervous system at work. But the relaying of such messages starts to falter in people with NMOSD.
With NMOSD, certain cells in your body attack different parts of the central nervous system, most commonly the optic nerve (the cable that connects the eye to the brain), the spinal cord (the long bundle of nerves that run along your backbone), and part of the brainstem (the base of your brain that regulates involuntary actions such as breathing and swallowing). Under attack, these areas swell and become inflamed, which can cause pain, loss of vision, weakness, numbness, paralysis, problems going to the bathroom, and range of other issues.
Of course, not every symptom crops up all at once during an NMOSD attack, and most symptoms only occur for a confined length of time. But still, an NMOSD attack can do lasting damage. “It comes thick, quick, and fast when it happens, and it can be devastating,” says Saif Huda, M.D., Ph.D., a neurologist at the Walton Centre Foundation Trust in the U.K.
Like multiple sclerosis, a disease NMOSD is often mistaken for, the condition is characterized by periods of normalcy punctuated with recurring relapses, when attacks on the central nervous system occur. These can be years apart. Fortunately, doctors now have effective treatments to help prevent or minimize such events. When an attack does occur, here’s a detailed look at what it can do to your body.
Even though NMOSD can affect your sight, it doesn’t damage the eye itself, says Ilya Kister, M.D., a neurologist and director of the Neuromyelitis Optica Treatment and Research Program at New York University Langone Medical Center. Instead, the disease causes the optic nerve to become inflamed, preventing it from properly transmitting signals from your eye to your brain, a condition called “optic neuritis.”
Inflammation of the optic nerve can distort vision in a few ways. Very often, people feel pain, particularly when moving their eye, accompanied by blurriness or loss of vision in one or (rarely) both eyes. An NMOSD attack could also cause part of your field of vision to disappear when you close one eye. Or color vision might fade, so everything appears tinted with grey.
These vision issues typically last for days or weeks and worsen over time. “It starts at a low burn and then it heats up,” describes Dr. Kister. After an attack, your vision usually improves, though often it doesn’t completely return to normal.
Weak Legs, Numb Arms
Your spinal cord is a long tube, as thick as a thumb, responsible for carrying messages between the brain and the body. During an NMOSD attack, a chunk of this pipeline becomes inflamed, an issue known as “transverse myelitis.” Often, this inflammation extends over three or more vertebrae and can lead to a wide range of issues, depending on where the spinal cord is impacted.
For instance, an attack might cause sudden weakness or loss of sensation in a leg or an arm, causing you to have trouble walking or difficulty using your hands. Often, numbness or weakness will start from your lower limbs and creep upwards. NMOSD can also cause paralysis of the legs and lower body, which may lead to loss of control going to the bathroom.
Other unexpected issues can crop up too, like intense, painful itching caused by inflammation of certain fibers in the spinal cord. Other times, inflammation leads to recurring spasms, where the muscles of an arm or leg are stuck in one position for 30 seconds or more.
In most cases, symptoms start off as mild and build up over days as inflammation in the spinal cord progresses. Eventually, the inflammation will lessen, but without treatment, it can result in lasting damage, even leaving patients wheelchair-bound after a particularly severe attack.
Your brainstem sits at the base of your skull, connecting your brain to the spinal cord. Sometimes during an NMOSD attack, inflammation travels to this area, affecting part of the brainstem called the area postrema. This region controls involuntary bodily actions such as hiccupping and vomiting. When it comes under siege during an NMOSD attack, it can cause incessant bouts of either (or both) behaviors. Fortunately, hiccups and puking are primary symptoms in only about one in 10 cases of NMOSD. But when they do occur, the disease can be very hard to diagnose. “It will look to all the world like someone has a major GI illness,” Dr. Kister says.
Why Your Body Attacks the Nervous System
Most people diagnosed with NMOSD have antibodies in their blood that attack a protein called aquaporin 4, which lives on certain cells of the central nervous system and helps move water across cell membranes. These antibodies wreak havoc on the nervous system, igniting a chain of events that results in inflammation.
Other people have a different type of antibody that attacks a protein called myelin oligodendrocyte glycoprotein (MOG) that helps protect the nerves. (A relatively new distinction, it's possible people with the MOG antibody may be classified as having a different, unique disease in the future.)
On the “bright” side, the presence of these antibodies means it’s easy to test for NMOSD. It’s a very rare condition, though: Only a few thousand people in the U.S. have the disease, and about a quarter million worldwide have been diagnosed. If you are one of the unlucky few, the good news is that there are a number of effective treatments which have come out in the last few years that help keep this condition under control. It’s possible to live a healthy life despite an NMOSD diagnosis with the right treatment plan in place.