Testing for Neuromyelitis Optica (NMO)
So, what is neuromyelitis optica? Neuromyelitis optica is a severe, inflammatory demyelinating disease of the central nervous system. Traditionally, neuromyelitis optica has been considered under the term Devic disease and in Asian countries has been considered under the term optic spinal multiple sclerosis. Neuromyelitis optica is a relapsing disease. It is really quite different to what Devic first described. Devic described a monophasic illness, whereas neuromyelitis optica is a relapsing illness. Neuromyelitis optica has a predilection for the optic nerves and spinal cord. It causes optic neuritis when impacting the optic nerve, and transverse myelitis when affecting the spinal cord. In order to have a diagnosis of neuromyelitis optica, by the criteria set forth by Dean Wingerchuck in the late 1990's, patients must have the presence of optic neuritis and myelitis. However, more recently, we have become to realize that there is a broader spectrum of neuromyelitis optica that now includes relapsing optic neuritis, in which case transverse myelitis may not occur, and relapsing transverse myelitis, in which case optic neuritis may not occur. When a patient presents with neuromyelitis optica, the brain MRI is generally normal.
Traditionally, it was considered that the brain MRI should remain normal; however, we have recognized that as the disease progresses the majority of patients with NMO develop brain lesions. Though in adults, brain symptoms are uncommon. As you can see on the right hand side of this slide, this is a T1 postcontrast image, coronal section, which shows you the optic chiasm enhancing. When patients with neuromyelitis optica present with an optic neuritis, they can present with it affecting the right optic nerve, the left optic nerve, sometimes patients will present with bilateral simultaneous optic neuritis, and occasionally, patients will present with sequential optic neuritis, in other words, it starts in the right eye and then moves to the left eye. The other area that is commonly involved in neuromyelitis optica is the spinal cord.
Here you can see a sagittal image, T-2 weighted, MRI of the cervical spine. And, you can see a long area of signal abnormality extending from the cervical medullary junction all the way down the cervical cord, over many segments. Transverse myelitis and neuromyelitis optica is longitudinally extensive. It usually extends greater than 3 vertebral segments. This is extremely unusual for multiple sclerosis in which the lesions are generally short, usually less than 1 vertebral segment. If a patient presents with a longitudinal extensive transverse myelitis, the physician should consider neuromyelitis optica in the differential diagnosis.
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