November 26, 2010
Dear Mayo Clinic:
What can you tell me about neuromyelitis optica? My husband was recently diagnosed. We hear it is often confused with multiple sclerosis. What are the differences between the two?
Neuromyelitis optica (NMO), also called Devic's disease, resembles multiple sclerosis in many ways. It was first identified in 1894 and characterized by its tendency to selectively and severely affect the optic nerve and spinal cord. But for about 100 years, NMO could not be distinguished from multiple sclerosis.
Research conducted over the past 10 years — much of it at Mayo Clinic — shows that NMO and multiple sclerosis are distinct illnesses that take different courses and need different treatments. Because of this, researchers have found ways to differentiate between these diseases and more quickly diagnose NMO.
Both diseases affect the central nervous system. In NMO and multiple sclerosis, the immune system reacts against the body in what are often termed episodes or attacks. These episodes cause inflammation and destruction of cells. In NMO, the primary targets are optic nerves and the spinal cord. The optic nerves and spinal cord are also commonly affected in multiple sclerosis.
Those are the similarities. But there are also a number of differences. Patients with NMO often have severe, rapidly worsening symptoms. When the optic nerves are affected, blindness can occur. Likewise, when spinal cord cells are damaged in NMO, patients may experience paralysis, loss of bladder and bowel control and, occasionally, breathing difficulties that can prove to be fatal. Patients with NMO may also have episodes of vomiting lasting for up to a month — not a symptom of multiple sclerosis.
In multiple sclerosis, initial episodes usually are mild and not life threatening. Over time, patients with multiple sclerosis may develop disabilities including paralysis (most typically in the legs), but permanent disability often tends to develop gradually and not as a result of sudden attacks as it does in NMO.
We've learned that patients with NMO usually have normal MRI brain scans early in the course of the disease, while the brain scans of patients with multiple sclerosis may show abnormalities. About 80 percent of patients with NMO have distinct, long lesions in the spinal cord on MRI that aren't present in patients with multiple sclerosis.
In the most significant discoveries so far, Mayo Clinic researchers have identified both a unique antibody associated with NMO and the target cell that the antibody destroys. Antibodies, activated by the body's immune system, are typically used to fight off infections. The antibody, called NMO-immunoglobulin G (NMO-IgG), is present in 70 percent of patients with NMO. Patients with multiple sclerosis do not have NMO-IgG. With these findings, researchers developed a blood test that greatly aids in accurate, rapid diagnosis of NMO, which is critical for improved outcomes.
The treatment options for these two illnesses also are quite different. Multiple sclerosis often is initially treated with interferon beta medications that work by reducing inflammation. These medications don't help patients with NMO and may actually cause more severe attacks than would otherwise occur.
Patients with NMO respond to immunosuppressive medications, such as azathioprine, mycophenolate mofetil or rituximab, to prevent future attacks. Plasma exchange — where antibodies are removed from the bloodstream — is successfully used to treat patients who don't respond to initial therapies. When plasma exchange is administered soon after an attack, patients may regain vision if blindness has occurred (or movement in the case of paralysis). When treatment is delayed by months, those functions can't be restored.
Your husband is dealing with a challenging disease, but it's helpful to have an accurate diagnosis early. He can be treated to prevent episodes. If attacks occur, treatment can help avoid devastating consequences.
— Brian Weinshenker, M.D., Neurology, Mayo Clinic, Rochester, Minn.