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How is NMO Diagnosed?
The medical history and clinical examination taken by a neurology specialist will include any previous symptoms or problems in the past to suggest a diagnosis of NMO.
It is also important to confirm the diagnosis by special investigations:
Magnetic Resonance Imaging (MRI) of the brain and spinal cord
MRI has become a key tool in the diagnosis of NMO. Magnetic fields are used to create images of the brain and spinal cord. The person lies in a long tube. The MRI scan takes approximately 30 minutes, it is painless but noisy and you have to lie very still.
The MRI of the brain is often normal in NMO although up to 60% people with NMO may have lesions on the brain, most are asymptomatic. These lesions tend to differ from MS lesions.
The MRI of the spine often shows inflammation extending over three vertebrae, usually affecting the cervical and thoracic areas, especially during a relapse. In MS, the spinal lesions tend to be short-segments (less than two vertebrae).
Cerebral Spinal Fluid (CSF) is the watery liquid that surrounds and protects the brain and spinal cord. A lumbar puncture (LP) requires a small amount of CSF to be drawn from the spinal cord with a needle. This only takes a few minutes and hurts a little and so is normally done under a local anaesthetic. Some people can get a headache after the procedure (due to leakage of CSF). It can be avoided by lying flat for a few hours after the test and having plenty to drink.
If done during an acute attack of TM there may be increased white cells and raised proteins. A special pattern of antibody proteins called oligoclonal bands (OCB) are usually absent in NMO.
Aquaporin 4 antibody (blood test)
The presence of Aquaporin 4 antibodies is highly specific to a diagnosis of NMO or NMO spectrum disorder. Most people (approximately 80%) have Aquaporin 4 antibodies present in their blood.
An ophthalmologist is trained to pick up even very small changes in a patient’s vision.
Opthalmoscopy (looking at the back of the eye with an ophthalmoscope) may show swelling of the optic disc. Often swelling is not seen, as the demyelination can be further away from the eye (retro bulbar neuritis).
Visual Evoked Potential (VEP)
Electrodes are placed on the scalp and measure the speed of nerve messages along the optic nerve from the eye to brain in response to being shown a flashing chessboard pattern on a computer screen. Damage to the optic nerve shows slower response time.
Visual Field Tests
These show whether there are any areas of your peripheral vision missing, which can indicate optic neuritis.
Low Contrast Test
By testing a person’s vision against increasingly faded images, it is possible to test how ‘washed out’ a persons vision has become.
This is a series of 13 images that detect minor changes in colour vision sensitivity.
Optical Coherence Tomography (OCT)
This is a very fast scan that can measure the thickness of the nerve fibres in the optic nerve. At present this is more a research tool than a clinical marker.
Diagnostic Criteria of NMO
Two Absolute criteria:
1. Optic Neuritis
2. Transverse Myelitis
At least 2 of 3 supportive criteria:
1. Presence of continuous spinal cord MRI lesion extending over three or more vertebral segments.
2. MRI brain not satisfying diagnostic criteria for MS.
3. Aquaporin 4 antibody present in serum.
NMO Spectrum Disorder
Optic neuritis OR Transverse myelitis AND presence of Aquaporin 4 antibodies in serum.