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Devic’s disease, also known as Devic’s syndrome or neuromyelitis optica (NMO), is an autoimmune, inflammatory disorder in which a person’s own immune system attacks the optic nerves and spinal cord. This produces an inflammation of the optic nerve (optic neuritis) and the spinal cord (myelitis). Although inflammation may also affect the brain, the lesions are different from those observed in the related condition multiple sclerosis.[1] Spinal cord lesions lead to varying degrees of weakness or paralysis in the legs or arms, loss of sensation, and/or bladder and bowel dysfunction.[2]
Devic’s disease is a rare disorder which resembles multiple sclerosis (MS) in several ways, but requires a different course of treatment for optimal results.[2] NMO has also been suggested to be a variant form of acute disseminated encephalomyelitis.[3][4] The likely target of the autoimmune attack at least in some patients with NMO has been identified. The target is a protein of the nervous system cells called aquaporin 4.[5]
The main symptoms of Devic’s disease are loss of vision and spinal cord function. As for other etiologies of optic neuritis, the visual impairment usually manifests as decreased visual acuity, although visual field defects, or loss of color vision may occur in isolation or prior to formal loss of acuity. Spinal cord dysfunction can lead to muscle weakness, reduced sensation, or loss of bladder and bowel control.[6] The typical patient has an acute and severe spastic weakness of the legs (paraparesis) or all four limbs (tetraparesis) with sensory signs, often accompanied by loss of bladder control.
Devic’s disease is similar to MS in that the body’s immune system attacks the myelin surrounding nerve cells. Unlike standard MS, the attacks are not believed to be mediated by the immune system’s T cells but rather by antibodies called NMO-IgG. These antibodies target a protein called aquaporin 4 in the cell membranes of astrocytes which acts as a channel for the transport of water across the cell membrane[2]. Aquaporin 4 is found in the processes of the astrocytes that surround the blood-brain barrier, a system responsible for preventing substances in the blood from crossing into the brain. The blood-brain barrier is weakened in Devic’s disease, but it is currently unknown how the NMO-IgG immune response leads to demyelination.
Most research into the pathology of Devic’s disease has focused on the spinal cord. The damage in the spinal cord can range from inflammatory demyelination to necrotic damage of the white and grey matter. The inflammatory lesions in Devic’s disease have been classified as type II lesions (complement mediated demyelinization), but they differ from MS pattern II lesions in their prominent perivascular distribution. Therefore, the pattern of inflammation is often quite distinct from that seen in MS. [2][7]
The Mayo Clinic proposed a revised set of criteria for diagnosis of Devic’s disease in 2006. The new guidelines for diagnosis require two absolute criteria plus at least two of three supportive criteria being:[8]
Absolute criteria:
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