Diagnosing the chronic immune system disorder neuromyelitis optica spectrum disorder, or NMOSD, typically involves a detailed medical history, a thorough clinical evaluation, and specialized imaging and laboratory tests.
In NMOSD, the immune system erroneously launches an inflammatory attack against healthy tissue in the nervous system, comprised of the brain and spinal cord, causing damage. Clinicians rely on international criteria in reaching a diagnosis of the progressive autoimmune disorder.
What are the diagnostic criteria for NMOSD?
International diagnostic criteria for NMOSD, published in 2015, outline six core clinical characteristics of the disorder. Each is indicative of damage to a particular part of the nervous system that is affected by NMOSD.
One of these common features is optic neuritis, which occurs when inflammation causes damage to the nerves that connect the eyes to the brain. Another common feature is inflammation of the spinal cord (myelitis). The remaining four features are inflammation in particular regions of the brain, specifically the brainstem, diencephalon, cerebrum, or the area postrema of the dorsal medulla. Inflammation to this last structure leads to vomiting and hiccups that appear suddenly and can last for weeks.
In each of these six areas, inflammation can be detected with imaging of the brain and spinal cord. Damage to these areas tends to cause particular symptoms. For example, optic neuritis frequently manifests as pain during eye movements and/or vision loss.
To qualify for a diagnosis of NMOSD, the international criteria state that a person must have at least one of these six core characteristics, and also test positive for autoantibodies that target the water channel aquaporin-4 (AQP4-IgG), which are characteristic of the disease.
In people with negative or unknown AQP4-IgG status, a diagnosis is given if two of the six core characteristics are met, in addition to specific features visible on imaging of the brain and spinal cord.
Since characteristics of pediatric NMOSD are similar to those of the adult disease, these criteria can generally be used in this patient population. However, some imaging features are less specific for diagnosing NMOSD in children than in adults.
The vast majority of NMOSD patients will test positive for AQP4-IgG, so testing for this self-reactive antibody can be instrumental in diagnosing the disease. This kind of testing is usually done with a blood sample. In rare cases, such as when blood testing yields inconclusive data, antibody testing may be done on the cerebrospinal fluid (CSF), which is the fluid that surrounds the brain and spinal cord.
Antibody testing can help to differentiate NMOSD from related disorders, particularly MOG antibody disease (MOGAD), which is characterized by self-targeting antibodies that attack a protein called MOG (myelin oligodendrocyte glycoprotein).
Magnetic resonance imaging (MRI) and related technologies can be used to scan the brain and spinal cord, allowing researchers and clinicians to identify areas where the tissue is damaged or inflamed. There are characteristic patterns of nervous system inflammation and damage in NMOSD, which can be used to help differentiate between NMOSD and other similar nervous system disorders, such as multiple sclerosis (MS).
The diagnostic criteria describe specific imaging features that are characteristic of NMOSD, which mainly include visible damage to the optic nerve, spinal cord, and/or other brain regions.
Other tests and differential diagnosis
During the diagnosis process, a neurologist may order an exam to measure muscle strength and coordination, identify potential numbness, and assess speech, vision, and cognitive function. An eye doctor also may be consulted.
No sign or symptom of NMOSD is pathognomonic. In other words, there is no feature of the disease that is unique to NMOSD, and is not found in any other condition. As such, a differential diagnosis — telling the difference between NMOSD and other diseases that might show similar symptoms — is critical.
A variety of different laboratory tests and clinical evaluations can help to distinguish between NMOSD and other conditions with similar symptoms or characteristics. For example, testing for infectious bacteria or viruses can help to rule out infection as a cause of symptoms. Tests for cancers or other autoimmune diseases can similarly rule out these other explanations.
Last updated: April 16, 2021
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