Reviewed by: HU Medical Review Board | Last updated: June 2022
Neuromyelitis optica spectrum disorder (NMO) is a rare autoimmune disease of the central nervous system (eye nerves, spinal cord, and brain). NMO may also be called neuromyelitis optica or NMO.1
In autoimmune diseases like NMO, the immune system cannot tell the difference between healthy cells and invaders like viruses, fungi, or bacteria. Because it cannot tell the difference, the body begins to attack and damage healthy cells. In NMO, the protective layer surrounding brain cells is targeted.1
It is important that the proper tests and exams are performed to get the diagnosis you need. NMO can be very similar to other severe brain and nerve diseases, but treatment differs with each of these diseases.1
Early diagnosis of NMO is important. The chance of lasting damage increases with each attack or episode of the disease.2
Who will diagnose me?
On your path to diagnosis, you will likely see at least 2 different doctors. You may first see your primary doctor, who will refer you to specialists. These may include:3,4
- Neurologist: This doctor specializes in diagnosing, treating, and managing disorders of the brain and nervous system. Some neurologists specialize in autoimmune disorders of the brain and nervous system.
- Ophthalmologist: This doctor specializes in eye and vision care and disorders. Ophthalmologists differ from other eye care specialists because they are licensed to practice medicine and perform surgery. Some ophthalmologists specialize in the nerves of the eye. These doctors are called neuro-ophthalmologists.
Antibodies and NMO
Antibodies are chemicals the immune system makes to kill germs. In some diseases, antibodies can also be harmful. One antibody that causes inflammation in the brain, eye, and spinal cord attacks a protein called aquaporin-4 (AQP4).5
AQP4 is found on brain cells called astrocytes and helps control water balance in the brain. The brain, spinal cord, and eye nerve (optic nerve) have AQP4. AQP4 antibodies (AQP4-IgG) damage the protective coating (myelin) of the brain cells and produce more proteins that lead to inflammation.5
I have AQP4 antibodies. Do I have NMO?
If you test positive for AQP4 antibodies (AGP4-IgG), you may be diagnosed with NMO if you have at least 1 of the following:2
- Inflammation of the optic nerve (optic neuritis)
- Inflammation of the spinal cord (transverse myelitis)
- Hiccups, nausea, or vomiting with no other cause
- Brain syndrome with damage to the brain (lesions) shown on MRI
I do not have AQP4 antibodies. Does that mean I do not have NMO?
While many with NMO test positive for AQP4 antibodies (AQP4-IgG), about 1 in 4 do not. This adds to the mystery of the disease. If you are negative for AQP4 antibodies (AQP4-IgG), you will be diagnosed with NMO only if you have optic neuritis or transverse myelitis and at least 1 other NMO symptom.2,6
How will diagnosis occur?
Various exams and tests will be used to help diagnose NMO.
Brain and nerve exams
Your neurologist will check a wide variety of functions during your brain and nerve exam (neurological exam), including:7
- Muscle movements and strength
- Memory and thinking (cognition)
Your doctor might test your blood for AQP4 antibodies (AQP4-IgG), which helps doctors differentiate NMO from multiple sclerosis (MS) and other brain or nerve conditions. This test helps doctors make an early diagnosis of NMO. Those who first test negative for AQP4 antibodies (AQP4-IgG) are often re-tested later if doctors suspect NMO.7
Antibodies targeting another protein called myelin oligodendrocyte glycoprotein (MOG) can also be present in NMO. They are believed to cause similar optic nerve or spinal cord attacks in MOG (MOG-IgG) antibody NMO. However, symptoms of this condition develop differently and need to be treated differently from those of AQP4 antibody (AQP4-IgG) NMO. Men and women are equally likely to get MOG antibody (MPG-IgG) NMO. Children have this disease more often than they have AQP4 antibody (AQP4-IgG) NMO.8,9
Optic neuritis occurs when inflammation damages the optic nerve. Optic neuritis is common in NMO. Because of this, your eye doctor (ophthalmologist) may be the doctor who diagnoses the condition or can be an important part of your team of doctors.7,10
Magnetic resonance imaging (MRI) uses magnetic fields to make detailed pictures of your organs. A brain and spine MRI is used to help diagnose NMO. This test creates detailed images of your brain, optic nerves, and spinal cord. Your doctor might be able to see lesions (areas of nerve damage) when diagnosing NMO.7
Cerebral spinal fluid (CSF) is the watery liquid that surrounds and protects the brain and spinal cord. A lumbar puncture (also called a spinal tap or LP) requires a small amount of CSF to be drawn from the space around the spinal cord with a needle. The needle is inserted into your lower back after numbing drugs are given to the area to decrease discomfort.7
Like blood work, this test might also help your doctor differentiate NMO from MS.7