Devic disease, now more commonly called neuromyelitis optica spectrum disorder (NMOSD), is a rare autoimmune condition where the immune system attacks the optic nerves and spinal cord. It was long considered a severe form of multiple sclerosis, but it is now recognized as a completely separate disease with distinct causes, treatments, and outlook. NMOSD affects roughly 1 to 10 per 100,000 people worldwide, with women diagnosed up to nine times more often than men.
How NMOSD Differs From Multiple Sclerosis
For decades, doctors grouped Devic disease with MS because both involve the immune system damaging nerve tissue. The critical distinction came in 2004, when researchers discovered that most people with NMOSD carry a specific antibody called aquaporin-4 IgG (AQP4-IgG). This antibody targets a water-channel protein found on certain support cells in the brain, spinal cord, and optic nerves. MS does not involve this antibody, and the pattern of damage is fundamentally different.
In MS, the immune system strips the protective coating (myelin) from nerves across many areas of the brain and spinal cord, usually causing mild to moderate relapses. In NMOSD, attacks tend to be fewer but far more severe, and they concentrate on the optic nerves and long stretches of the spinal cord. An MRI of someone with NMOSD typically shows spinal cord inflammation spanning three or more vertebral segments, while MS lesions are usually shorter. This difference matters because it changes both treatment and prognosis.
What Causes the Immune Attack
In roughly 70 to 80 percent of NMOSD cases, the immune system produces antibodies against aquaporin-4, a protein that helps regulate water balance in the central nervous system. These antibodies bind to cells called astrocytes, triggering intense inflammation that damages both the astrocytes and the surrounding nerve fibers. The result is tissue destruction that goes deeper than the myelin stripping seen in MS.
A smaller subset of patients, perhaps 10 to 25 percent, test negative for the aquaporin-4 antibody but carry a different antibody targeting a protein called myelin oligodendrocyte glycoprotein (MOG). This variant behaves somewhat differently and often has a better prognosis. The remaining patients test negative for both antibodies but still meet the clinical criteria based on their symptoms and imaging.
What triggers the immune system to produce these antibodies in the first place isn’t fully understood. NMOSD is not directly inherited, but certain genetic factors related to immune regulation appear to increase susceptibility. It can occur alongside other autoimmune conditions like lupus or Sjögren’s syndrome, suggesting a broader tendency toward immune dysfunction in some patients.
Symptoms and How Attacks Feel
NMOSD typically presents as distinct attacks (relapses) separated by periods of stability. The two hallmark presentations are optic neuritis and transverse myelitis, though other patterns occur as well.
Optic neuritis causes rapid vision loss in one or both eyes, often accompanied by eye pain that worsens with movement. Vision can deteriorate over hours to days, ranging from blurriness to near-total blindness in the affected eye. Unlike the optic neuritis seen in MS, which usually resolves well, NMOSD-related episodes tend to cause more severe and lasting vision damage if untreated.
Transverse myelitis involves inflammation across a wide section of the spinal cord, producing weakness or paralysis in the legs (and sometimes arms), numbness or painful sensations below the level of inflammation, and bladder or bowel dysfunction. Some people experience painful spasms or a tight banding sensation around the torso. Because NMOSD lesions span long segments of the cord, attacks can be devastating, sometimes causing complete paralysis from the waist down within days.
Other possible symptoms include intractable hiccups and nausea lasting days or weeks (caused by inflammation in the brainstem), excessive sleepiness, and, in rare cases, brain involvement that can mimic stroke-like episodes. The disease follows a relapsing course in about 90 percent of patients, meaning new attacks occur unpredictably over months or years. A small minority experience a single episode without recurrence, though this is hard to predict at onset.
How It’s Diagnosed
Diagnosis starts with the clinical picture: sudden, severe optic neuritis or transverse myelitis, especially when both occur close together. The most important confirmatory test is a blood test for the aquaporin-4 antibody. A positive result, combined with a compatible clinical attack, is usually enough to establish the diagnosis with high confidence.
MRI plays a supporting role. Spinal cord imaging typically shows a long lesion extending over three or more vertebral segments, a pattern that strongly suggests NMOSD over MS. Brain MRI may be normal early on or show lesions in specific locations characteristic of the disease, particularly around the brainstem and areas rich in aquaporin-4.
For patients who test negative for the aquaporin-4 antibody, doctors may test for MOG antibodies and rely more heavily on imaging patterns and clinical features to distinguish the condition from MS. Getting the diagnosis right is critical because several MS medications can actually worsen NMOSD.
Treatment During Attacks
Acute attacks are typically treated aggressively because the damage from each relapse can be permanent. The first-line approach is high-dose corticosteroids given intravenously over several days to suppress the inflammatory response. If steroids don’t produce meaningful improvement, plasma exchange (sometimes called plasmapheresis) is often used next. This procedure filters the harmful antibodies out of the blood and can produce dramatic recovery in some patients, particularly when started early.
Recovery from an individual attack varies widely. Some people regain most of their lost function over weeks to months. Others are left with significant residual disability, especially after spinal cord attacks. The cumulative effect of repeated relapses is the main driver of long-term disability in NMOSD, which is why preventing future attacks is the central goal of ongoing treatment.
Long-Term Prevention
Unlike MS, where dozens of approved therapies exist, NMOSD treatment has historically relied on general immune-suppressing medications. That changed significantly starting in 2019, when the first therapies specifically designed for NMOSD began receiving approval. These newer treatments target precise parts of the immune pathway involved in the disease.
One class of therapy works by depleting a type of immune cell (B cells) that produces the harmful antibodies. Another blocks a component of the immune system’s inflammatory cascade called complement, which plays a direct role in the tissue destruction seen in NMOSD. A third approach blocks a signaling molecule that promotes the survival of antibody-producing cells. In clinical trials, all three approaches reduced the risk of relapse by 70 to 95 percent compared to placebo, a remarkable improvement over older options.
These targeted therapies are given as intravenous infusions or injections on schedules ranging from every two weeks to every six months, depending on the specific treatment. Most people with NMOSD remain on preventive therapy indefinitely, since stopping treatment carries a high risk of relapse. The choice of therapy depends on antibody status, other health conditions, and practical considerations like infusion access.
Living With NMOSD
The prognosis for NMOSD has improved substantially with modern treatments. Before targeted therapies were available, about 50 percent of patients with relapsing disease developed severe visual impairment or required a wheelchair within five to ten years. With current prevention strategies, many people experience few or no relapses and maintain their independence long-term.
Between attacks, people with NMOSD often deal with lingering effects from previous relapses: chronic nerve pain, fatigue, spasticity, bladder issues, or reduced vision. These residual symptoms benefit from rehabilitation, pain management, and adaptive strategies rather than the immune-targeting drugs used to prevent new attacks. Fatigue, in particular, is one of the most commonly reported ongoing challenges.
Pregnancy requires careful planning because some preventive therapies must be paused, and the postpartum period carries an increased risk of relapse. Working with a neurologist experienced in NMOSD before conception allows for medication adjustments that balance relapse prevention with fetal safety. The disease itself does not appear to reduce fertility or directly harm the pregnancy.
Because NMOSD is rare, many general neurologists see only a handful of cases in their careers. Connecting with a specialist center or an NMOSD-focused neurologist can make a meaningful difference in both diagnosis time and treatment quality. Patient organizations like the Guthy-Jackson Charitable Foundation and the Siegel Rare Neuroimmune Association maintain directories of specialists and offer peer support networks.