An Overview of Neuromyelitis Optica Spectrum Disorder

Neuromyelitis optica spectrum disorder (NMOSD) is a rare disease of the brain and spinal column. The primary symptoms involve inflammation of the optic nerve (optic neuritis) and spinal column (myelitis).

The condition is chronic. It often begins during childhood, but it can also begin in adulthood (often during a person’s 40s). It is characterized by severe, debilitating symptoms that can result in blindness and paralysis. These severe symptoms result from what is called “demyelinating autoimmune inflammatory process” which affects the central nervous system (the brain and spinal column).

Demyelinating autoimmune inflammation occurs when the immune system attacks the covering of the nerves, called the myelin sheath. The myelin sheath is designed to protect the nerves. When this protective layer is damaged, inflammation and injury to the nerve fibers occur, eventually leading to multiple areas of scarring (called sclerosis). In NMOSD, the nerves that are involved are primarily the optic nerves (nerves that carry signals from the eyes to the brain) and the spinal cord.

Common symptoms of NMOSD may include:

• Eye pain
• Loss of vision
• Weakness in the upper and lower extremities (arms and legs)
• Paralysis of the upper and lower extremities
• Loss of bladder control
• Loss of bowel control
• Uncontrollable hiccups and vomiting

The condition usually involves episodes that may occur months or even years apart. Between flare-ups, some people are symptom-free. This asymptomatic period is referred to as being in remission.

The cardinal symptoms of NMOSD come from one of two processes, including:

1. Optic neuritis: This is inflammation of the optic nerve, leading to pain inside the eye and a disturbance in clear vision (acuity). Either one eye is affected (unilateral optic neuritis) or both eyes could be symptomatic (called bilateral optic neuritis).
2. Myelitis: This is sometimes referred to as “transverse myelitis” because of the involvement of the motor, sensory, and autonomic function (the nerves that govern bowel and bladder control). Transverse myelitis can cause sudden impairment of sensation, motor control, and autonomic function (sometimes within 24 hours). Symptoms of NMOSD may be identical to those of transverse myelitis with an unknown cause.

Symptoms of myelitis may include:

• Headaches and back pain
• Pain in the arms, legs or spine
• Mild to severe paralysis (called paraparesis when it’s partial paralysis and paraplegia when it’s a complete loss of sensation and motor function)
• Loss of bladder or bowel control
• Sensory loss

In the initial stages of the disorder, NMOSD can be easily confused with multiple sclerosis (MS) and is often misdiagnosed.

Medical experts used to believe that NMOSD was simply a form of multiple sclerosis, but today they think that perhaps it is a different condition altogether. Although some of the symptoms are very similar, symptoms are more severe in those with NMOSD than in those with MS. Another difference is that those with NMOSD often have vision problems in both eyes, while multiple sclerosis is more commonly known to cause vision problems in just one eye.

There are two types of NMOSD, including:

1. Relapsing form: This involves flare-ups that occur with periods of recovery between episodes. This type is the most common form of NMOSD, with women more likely to be affected than men.
2. Monophasic form: This consists of a single episode lasting 30 to 60 days. Men and women are equally apt to get this type of NMOSD.

Possible complications of neuromyelitis optica spectrum disorder include:

• Blindness or visual impairment
• Paralysis of one limb
• Stiffness, weakness, or muscle spasms
• Loss of bladder or bowel control
• Depression
• Chronic fatigue

Although the exact cause of NMOSD has not yet been discovered, over 90% of those with NMOSD report that they have no known relatives with the condition. In half the cases, people diagnosed reported having a family history of some type of autoimmune disease. This indicates a strong possibility that NMOSD is linked with a genetic predisposition. But the underlying cause of autoimmunity is not well understood.

NMOSD is one of a diverse group of diseases which involve a specific protein that functions as an antibody (called the aquaporin-4 [AQP4] autoantibody). While antibodies normally attack and kill pathogens such as bacteria and viruses, when a person has an autoimmune disease such as NMOSD, some of the antibodies attack the person’s own proteins instead of attacking pathogens.

There are several tests aimed at diagnosing NMOSD. Your health care provider may perform several diagnostic tests if NMOSD is suspected, including:

• A magnetic resonance imaging (MRI) scan of the brain and spinal cord
• Various tests to evaluate the function of the optic nerves
• Blood tests to check for biomarkers (measurable substances in which, when present, can predict the presence of a disease)
• Spinal fluid samples to check for a biomarker called an AQP4-Ab (this biomarker can differentiate between multiple sclerosis and NMOSD)

NMOSD is considered incurable, but according to a 2016 study, there are several treatment modalities aimed at alleviating symptoms. This is called palliative treatment, and may include:

• Corticosteroid medication: Prevents relapses; given during an acute (severe, short-term) attack
• Immunosuppressants: Slow down the immune system’s attack on the nerves
• Plasmapheresis: A procedure found to effectively remove anti-AQP4 antibodies from the blood. May result in an improvement in symptoms of neurological disability, such as paralysis.
• Pain medications
• Azathioprine: A medication given as a preventative treatment for a range of autoimmune diseases

The debilitating symptoms that can occur in those with NMOSD can be devastating, particularly considering this is a relatively young person’s disease. The symptoms could progress to paralysis, blindness, or they may even involve the muscles that control breathing. Because of the wide range of different symptoms of NMOSD, each person’s prognosis and treatment will be different. Taking control of the things you can do, such as building a support network—as well as learning to let go of the things you cannot control—are vital coping skills for those with NMOSD who aim to maintain the highest quality of life possible.