Neuromyelitis Optica (NMO) Spectrum Disorder is a chronic, sometimes debilitating disease that affects the visual pathways (optic neuritis) and the spinal cord (myelitis). NMO is a rare autoimmune disease, but significant progress has been made to expand the treatment options available, says Rachel Brandstadter, MD, a neurologist at the Penn Multiple Sclerosis and Related Disorders Center and a specialist in NMO.
Dr. Brandstadter says that at its onset, NMO may be misidentified as multiple sclerosis because both may cause optic neuritis and myelitis. However, in those with NMO, these symptoms tend to be more severe.
Who Is Affected by NMO?
The prevalence of NMO in the United States can vary by the source, but Dr. Brandstadter believes that it lies just shy of four Americans per 100,000. It appears with greater frequency in people of African and Asian descent (between 4 and 10 per 100,000).
The disease can affect anyone at any age, but it's most common in the United States among women in their thirties.
NMO is considered an autoimmune disease, which occurs when your body's immune system mistakenly targets healthy tissue as foreign. Most patients with NMO will have detectable aquaporin-4 immunoglobulin G (AQP4-IgG) antibodies, which is an important water channel concentrated in specific parts of the brain and spinal cord.
However, some will have antibodies against a different target (myelin oligodendrocyte glycoprotein (MOG)), which is now recognized as a distinct clinical syndrome.
More than 95 percent of those diagnosed with NMO report no family history of the disease. Patients with NMO may also have other autoimmune conditions though.
What Happens in the Body When You Have NMO?
There are three "cardinal" symptoms of NMO:
- Optic Neuritis, inflammation of the optic nerve, which can lead to trouble seeing and pain with eye movement. Visual loss associated with NMO can occur in one or both eyes and can be severe.
- Myelitis, an inflammation of the spinal cord, which can lead to weakness or paralysis in the arms or legs, walking difficulties, loss of sensation, and/or impaired bowel and bladder control.
- Uncontrollable vomiting or hiccups, which results from the inflammation in part of the brainstem.
Someone diagnosed with NMO, Dr. Brandstadter says, will experience at least one of these three cardinal symptoms. Patients with NMO may experience repeated bouts of inflammation, or relapses, separated by periods of remission that can last weeks, months, or years.
High-dose corticosteroids and/or plasma exchange can alleviate symptoms of a severe NMO relapse. However, NMO relapses can be severe enough to cause permanent visual impairment or problems with walking.
To make the diagnosis, a detailed patient history is taken, and a thorough clinical evaluation is conducted. The doctor may also request blood work and brain and spinal cord MRIs to look for NMO's signature antibody, which is used to differentiate between MS and NMO. "There's a pathogenic antibody that's present in certain areas of the brain and spinal cord of many individuals with NMO, and it will turn up in the blood work," says Dr. Brandstadter.
How is NMO Treated?
The treatment of NMO, according to Dr. Brandstadter, generally falls into two categories: therapies for prevention of relapses and those that target existing NMO symptoms, such as sensory disturbance, pain, spasms, and bladder dysfunction.
In 2019, the US Food and Drug Administration (FDA) approved the first medication designed specifically for the treatment of NMO, Soliris (eculizumab). Last year, two more followed, Uplizna (inebilizumab) and Enspryng (satralizumab).
"The emergence of three targeted immunotherapies proven to reduce relapse risk in NMO has decidedly transformed the landscape of treatment for this rare and severe neuroinflammatory disorder," Dr. Brandstadter wrote in a peer-review article about the medications she co-authored with Amit Bar-Or, MD, FRCPC.
"We have more to learn about the long-term efficacy and safety of these agents," she says, "but these breakthroughs should be a source of hope for patients and their doctors."
There are also a number of "off-label" drugs that have been effectively used for years in the treatment of NMO. The standard treatment for NMO relapses are high-dose intravenous corticosteroids and plasma exchange. A variety of immunomodulatory drugs are employed for the long-term suppression of the disease.
Dr. Brandstadter says an accurate diagnosis is "supremely important" with NMO because certain disease-modifying therapies used in the treatment of multiple sclerosis can worsen NMO symptoms. Given the potential severity of relapses in NMO, any missteps could have a profound impact. "So we are dearly dedicated," Dr. Brandstadter says, "to making the correct diagnosis and preventing relapses through evidence-based treatments."