Devic’s disease, now called neuromyelitis optica spectrum disorder (NMOSD), is a rare autoimmune condition in which the immune system attacks the optic nerves and spinal cord. It affects roughly 0.07 to 10 people per 100,000 worldwide, and it can cause permanent vision loss, paralysis, and other serious neurological damage. Though it was once considered a form of multiple sclerosis, it is now recognized as a distinct disease with its own biological cause, diagnostic criteria, and treatment path.
How NMOSD Damages the Nervous System
In most people with NMOSD, the immune system produces an antibody that targets a specific water-channel protein found on cells called astrocytes. These cells wrap around blood vessels in the brain and spinal cord, forming part of the barrier that protects nerve tissue. When the antibody binds to this protein, it triggers the body’s complement system, a cascade of immune proteins that destroys the astrocytes. The resulting inflammation damages nearby nerve fibers, leading to the symptoms of the disease.
There is also a complement-independent mechanism at work. The antibody can cause the astrocyte to absorb and remove its own water channels from the cell surface, further disrupting normal function even without the full inflammatory cascade.
Common Symptoms
NMOSD symptoms stem from inflammation in two main areas: the optic nerves and the spinal cord. Optic nerve inflammation (optic neuritis) causes blurred vision or vision loss in one or both eyes, difficulty seeing color, and eye pain. Spinal cord inflammation (transverse myelitis) causes stiffness, weakness, or numbness in the legs and sometimes the arms, along with tingling or shooting pain in the neck, back, or stomach. Many people also develop problems with bladder or bowel control.
Some symptoms are less expected. Persistent hiccups and uncontrollable nausea or vomiting can occur when inflammation hits a structure in the brainstem called the area postrema. In children, seizures, confusion, or even coma are possible. Symptoms typically come in episodes called relapses, where they flare up and then partially improve, only to return again later. Each relapse carries a risk of permanent damage.
Who Gets It
NMOSD overwhelmingly affects women, with a female-to-male ratio of about 9 to 1. The highest prevalence rates have been found in the French West Indies and South Korea, while the lowest are in Cuba and Australia. It can appear at any age but most commonly strikes in adulthood. People of African and Asian descent appear to be disproportionately affected compared to those of European descent.
Two Antibody Types, Two Different Outlooks
Not everyone with NMOSD has the same antibody. The majority test positive for the water-channel antibody (AQP4-IgG), which tends to cause more severe disease. A smaller group tests positive for a different antibody that targets a protein called MOG, found on the insulating layer around nerve fibers.
These two groups look clinically different. People with MOG antibodies are more often male, more frequently have optic neuritis affecting both eyes at once, and tend to have spinal cord lesions in the lower portion of the spine rather than higher up. Critically, they also tend to recover better after attacks, with less lasting visual impairment and fewer relapses overall. Some experience only a single attack and never relapse. By contrast, AQP4-positive patients generally face a more relapsing course and a higher risk of accumulating permanent disability.
How It Differs From Multiple Sclerosis
NMOSD and multiple sclerosis (MS) can look similar early on, since both can cause optic neuritis and spinal cord problems. But the two diseases behave differently in ways that matter for treatment and prognosis.
On spinal MRI, NMOSD produces long, continuous lesions that stretch across three or more vertebral segments and sit centrally within the spinal cord. MS lesions are typically shorter (rarely spanning more than one vertebral segment), patchy, and located near the outer edge of the cord. Brain MRI is another distinguishing factor: most NMOSD patients have no brain lesions or only a few nonspecific white matter spots, while MS typically shows a characteristic pattern of brain lesions. Attacks in NMOSD also tend to be more severe and sudden than in MS, and spinal fluid analysis in NMOSD often shows a higher white blood cell count.
Getting the distinction right matters because some MS treatments can actually worsen NMOSD.
How It Is Diagnosed
Diagnosis follows international consensus criteria established in 2015. For patients who test positive for the AQP4 antibody, the threshold is straightforward: at least one clinical attack involving one of six recognized patterns of nervous system inflammation. For patients who test negative, or whose antibody status is unknown, the bar is higher. They must have experienced at least two different types of clinical events affecting different parts of the nervous system, and MRI findings must match specific patterns. At least one of those events must be optic neuritis, transverse myelitis with a long spinal cord lesion, or a brainstem syndrome with a corresponding brain lesion.
In all cases, other possible diagnoses must be ruled out before NMOSD is confirmed.
Treating Acute Attacks
When a relapse hits, the first-line treatment is high-dose intravenous steroids, typically given over five days. Not everyone responds. Complete recovery occurs in only about 17 to 35% of relapses. For those who don’t improve on steroids, plasma exchange is the next step. This procedure filters the blood to remove the harmful antibodies and is usually given in five to seven sessions over the following week.
In a U.S. study tracking patients over a median of two years, nearly half (47.7%) experienced one or more relapses, with an average relapse rate of about 0.8 per year. Relapses lasted an average of nearly 13 days, and about 17% of patients had relapses lasting 20 days or more. Each attack that doesn’t fully resolve adds to the cumulative burden of disability.
Preventing Future Relapses
Because each relapse risks permanent damage, long-term preventive therapy starts as soon as NMOSD is diagnosed. Two treatments have been approved specifically for AQP4-positive adults. The first, approved in 2019, works by blocking part of the complement system, the same immune cascade that destroys astrocytes. It is given as a regular infusion and requires vaccination against meningococcal bacteria beforehand, because suppressing complement raises the risk of certain bacterial infections.
The second, approved in 2020, works by depleting a type of immune cell involved in antibody production. It is also given by infusion and carries risks including infusion reactions, reactivation of hepatitis B, and a gradual decline in the body’s overall antibody levels over time, which can increase susceptibility to infections.
Before these targeted therapies existed, doctors relied on general immune-suppressing medications. Those older options are still used in parts of the world where newer treatments are unavailable, or for patients who test negative for the AQP4 antibody and fall outside the approved indications.
Long-Term Outlook
NMOSD is a serious condition, but the outlook has improved significantly with modern treatment. Without preventive therapy, relapses tend to accumulate over time, and each one carries the risk of lasting vision loss or paralysis. Over years, this can lead to total blindness, inability to walk, or both. The disease does not follow the slow, progressive worsening pattern seen in some forms of MS. Instead, disability accumulates in a stepwise fashion, driven entirely by relapses.
This is why relapse prevention is the central goal of treatment. Patients on effective maintenance therapy can go years without attacks, preserving the function they have. Those with MOG antibodies generally fare better than those with AQP4 antibodies, experiencing fewer relapses and recovering more fully when they do occur. Early diagnosis and prompt initiation of preventive treatment offer the best chance of limiting long-term disability.