Related Diseases: NMO
In 2013, the Rocky Mountain MS Center Board of Directors expanded the mission of the MS Center to include related diseases. Patients with these diseases, which share traits with multiple sclerosis and tend to be rare, often find themselves without a medical home. With the expansion of our mission, they now have a home at the Rocky Mountain MS Center and receive excellent care from MS Center physicians. In an effort to increase awareness and education around these related diseases, the Rocky Mountain MS Center will be presenting a series of articles to help introduce readers to all of the conditions now included in our expanded mission. The first article in this series, provided below, will focus on neuromyelitis optica (NMO).
In the last century, our understanding of MS was crude. It was only in 1993 that the first disease modifying therapies emerged. Since then we have learned a lot and refined our understanding by teasing out different aspects of the disease. This has made one major milestone possible: our ability to distinguish between MS and NMO. Neuromyelitis optica (NMO), also known as Devic’s disease and optic-spinal MS, is an immune-mediated disease that primarily affects the optic nerves and spinal cord.
NMO was first recognized in 1870 as a disease of both spinal cord inflammation and loss of vision. It was thought to be a type of MS until the early 2000s when new information allowed the two conditions to be distinguished from one another. This was possible after the discovery of a biomarker: an antibody (IgG) that recognizes a protein called Aquaporin 4. It is often called NMO-IgG. Although about one quarter of patients with NMO symptoms are NMO-IgG negative, the majority of NMO patients test positive for this biomarker. Identifying this biomarker has dramatically changed our understanding of NMO, especially in how we diagnose and treat patients with the disease. Proper diagnosis is critical because NMO and MS treatments generally differ.
NMO is uncommon; about one in 100,000 people will develop it.
Common symptoms of NMO include:
- Optic neuritis: inflammation of the optic nerve resulting in blurred or loss of vision, decreased color vision, or a blind spot.
- Transverse myelitis: inflammation of the spinal cord. The lesions that appear on an individual’s MRI are usually longitudinally extensive—meaning that they span three or more vertebrae—and can result in weakness, numbness, balance difficulties, and bowel and bladder problems.
- Brainstem lesions can also sometimes occur, especially in kids, resulting in nausea and vomiting and, sometimes, balance problems.
Work-up
The diagnostic work-up for NMO involves an MRI of the brain. NMO and MS brain lesions are different, and the MRI makes it possible to clarify which of the two are present. Full spine MRI imaging is also performed to evaluate lesion length and number. A lumbar puncture (spinal tap) is useful because patients with NMO do not generally have oligoclonal bands or elevated IgG index, which are common in MS. The NMO biomarker—Aquaporin 4—test is normally run on blood because the antibody concentration is generally much higher in blood than in spinal fluid. Finally, depending on the situation, physicians may also perform visual evoked and/or OCT testing to evaluate if there has been any damage to the optic nerves.
The current diagnostic criteria for NMO, revised in 2006, are:
- Optic neuritis
- Transverse myelitis
- At least two of the following three criteria
- MRI evidence of a contiguous spinal cord lesion 3 or more segments in length
- Brain MRI non-diagnostic for multiple sclerosis
- NMO-IgG seropositivity (Aquaporin 4)
If the patient does not meet all of the above criteria, but has had either transverse myelitis or optic neuritis and they test positive for NMO-IgG, another diagnosis can be made: NMO spectrum disease, which is treated similarly to NMO.
Treatment
MS and NMO are treated differently. There are several studies suggesting that interferons worsen NMO, and therefore immunosuppressive drugs are preferred. The three main medications that are used for NMO are Imuran, Cellcept and Rituximab. Acutely, NMO is treated with steroids and—if deemed necessary—plasmapheresis. Plasmapheresis—the removal, treatment and return of blood plasma—helps to reduce antibody levels in the blood, which tend to go up during relapses.
Prognosis
Now that we can distinguish NMO from MS and recognize the need to treat them differently, patients with NMO can do quite well.