Neuromyelitis optica

Overview

The condition known as neuromyelitis optica (NMO), which can also be referred to as Devic disease and neuromyelitis optica spectrum disorder (NMOSD), is a rare chronic condition of the central nervous system that causes inflammation in the nerves of the eye, the spinal cord. It is an autoimmune disease, which means that the immune system wrongly attacks certain areas of the central nervous system. This primarily occurs in the spinal cord and optic nerves, which link the retina of the eye with the brain. However, it can also happen in the brain. 

The condition could develop following an infection. It might also be connected to another autoimmune disorder. Irregular antibodies attach to proteins within the central nervous system, resulting in harm.

Multiple sclerosis (MS) is frequently misdiagnosed as neuromyelitis optica, or it is thought to be a subtype of MS. NMO, however, is a different disease.

One or both eyes may become blind as a result of neuromyelitis optica, which can also result in arm or leg weakness or paralysis , and painful spasms. In addition, spinal cord damage can result in loss of sensation, uncontrollable vomiting, hiccups, and bladder or bowel issues. Children may experience comas, seizures, or confusion.

Relapses are frequent, and preventing recurring attacks is essential to avoiding disability. Although neuromyelitis optica flare–ups may be treatable, they can sometimes be severe enough to result in permanent vision loss and mobility issues.

Symptoms

NMO creates symptom “attacks,” which refers to intermittent (come and go) symptoms. Attacks may last for several days or even months. These types of attacks are frequently severe and can result in permanent damage. When this occurs, even after an attack has ended, the effects could still last. 

Three categories of NMO symptoms can be identified and include: 

• Optic neuritis: The optic nerve, which connects their eyes to their brain, receives signals from the eyes as they gather light from their environment. The patient’s perception of sight is then provided by the brain’s processing of those signals. Optic neuritis leads to inflammation of the optic nerve, resulting in its swelling. Given the limited space within the head, this swelling can exert excessive pressure on the optic nerve.

One or both of the optic nerves are inflamed, which causes these symptoms.

• • Eye pain: When the patient moves affected eye(s), this frequently takes place or becomes worse.
  • Blurry vision: When the patient is physically active, this symptom could worsen.
  • Partial or complete vision loss: Patient may experience complete or partial blindness in one eye (loss of the center of the field of vision is one example). Their vision may also become dim or they may have problems seeing colors.
  • Problem seeing in low light: Certain nighttime activities, including driving, may become challenging. 
• Myelitis: Inflammation of the spinal cord is known as myelitis. The spinal cord or surrounding spinal nerves may become compressed as a result of that swelling brought on by the inflammation. As a result, nerve signals that try to flow through the affected region may be partially or completely blocked. 

The presentation of myelitis symptoms is contingent upon the location of the inflammation and which segments of the spinal cord or spinal nerves are impacted. Common symptoms of myelitis include:

• • Muscle weakness or paralysis: Body parts farther down from the damaged spinal nerves and/or below the affected region of the spinal cord are affected. This may make it difficult to use both arms and hands, or it may make it difficult to stand or walk. Myelitis can cause paralysis or weakening in the breathing muscles if it affects the cervical spinal cord, which is the portion of the spinal cord in the back of the neck.
  • Spasticity: This occurs when the muscles contract independently due to a lack of control signals from the brain. As a result, muscles start to flex or tighten uncontrollably.
  • Pain: Myelitis can put pressure on the spinal cord and create pain. The swelling itself may cause the pain, or it may make the damaged nerves send pain signals incorrectly.
  • Incontinence: Their ability to regulate when they pee (urinate) or poop (defecate) can be affected by myelitis, which can interfere with the nerve signals that control their bladder and bowels. Bowel or urine incontinence may result from those muscles being uncontrolled.
  • Sexual dysfunction: The nerve signals that regulate the sexual organs or sexual activities can be interfered with by myelitis.
• Brain function disruptions: It is more typical for people with multiple sclerosis (MS) to experience alterations in their brain, although this is less typical for people with NMO. When it occurs, it may interfere with how their brain manages particular bodily functions. These disturbances can result in serious or even dangerous issues if they affect the brainstem or hypothalamus.

The brainstem may be affected by NMO, which might result in the following symptoms:

• • Hiccups that is uncontrollable.
  • Itching (pruritus) that is uncontrollable.
  • Unexplained nausea and vomiting 
  • Hearing loss.
  • Double vision (diplopia) 
  • Uncontrollable eye movements (nystagmus) 
  • Facial paralysis (palsy).
  • Dizziness or vertigo.
  • Difficulty with balance or coordination (ataxia).
  • Trigeminal neuralgia (nerve–based pain in the face)

The hypothalamus manages autonomic body processes. When NMO affects it, it can lead to disruptions in other bodily systems. A notable instance of this is NMO with narcolepsy.

Causes

Our understanding of NMO’s causes and mechanisms remains limited, and experts have only been able to offer partial explanations for its occurrence. Their knowledge is grounded in the following factors, although uncertainties persist:

• Immune system malfunctions: As an autoimmune disorder, NMO results when the body’s immune system incorrectly targets a body part. In this instance, it affects the spinal cord and/or optic nerves.

NMO has two recognized autoimmune forms:

• • Aquaporin–4 (AQP4) antibodies: A protein called AQP4 is present on the surface of several cells in the nervous system. Its function is to transport water into and out of cells. Unintentionally instructing the immune system to attack this protein, AQP4 antibodies harm the cells that have it on their surface. AQP4 antibodies are found in the blood of more than 80% of NMO patients.
  • Myelin oligodendrocyte glycoprotein (MOG) antibodies: MOG is a protein responsible for the formation and upkeep of the myelin sheath covering neurons. The myelin sheathing on the neurons is disrupted when MOG antibodies wrongly instruct the immune system to attack this protein. This antibody is present in the blood of about 6.5% of NMO patients.

These immune system irregularities predominantly occur for reasons that remain largely unidentified. Nevertheless, available data implies a potential link between these malfunctions and previous infections.

Currently, experts cannot ascertain the cause of NMO in individuals lacking AQP4 or MOG antibodies, constituting approximately 13.5% of those affected by this condition. These cases are categorized as “idiopathic,” signifying that they occur for reasons that remain unknown.

• Other autoimmune or inflammatory conditions: NMO can occur on its own, although it is more common in persons who also have autoimmune or inflammatory diseases. Before researchers can conclude that these circumstances can either cause or contribute to NMO, more investigation is required.

These conditions include may include systemic lupus erythematosus (SLE), celiac disease, Sjogren’s syndrome, disease, sarcoidosis, myastenia gravis, or antiphospolipid syndrome. 

• Genetics: Genetic factors may contribute to NMO, according to experts. The fact that people of particular racial or ethnic backgrounds are more likely to have this medical condition is one reason they suspect it. One such factor is that 3% of NMO cases include members of the same family. Although there is no proof that NMO can be passed down through the family, there may be hereditary variables that make NMO more likely to occur.

Risk factors

The following factors increase the risk in developing NMO.

• Age: People between the ages of 30 and 40 are typically affected. NMO in children is extremely rare, accounting for approximately 5% of occurrences.
• Gender: Women make up 80% to 90% of cases of NMO, making them the group most likely to be affected.
• Race: NMO can occur in persons of all racial and ethnic backgrounds, but it doesn’t do so equally across all groups. People of African origin, particularly those from the African Caribbean, are more likely to experience NMO.