Neuromyelitis optica

Devic's disease Classification and external resources ICD- 10 G 36.0 ICD- 9 341.0 DiseasesDB 29470 MeSH D009471 Neuromyelitis optica(NMO), also known asDevic's diseaseorDevic's syndrome, is an heterogeneous conditionconsisting of recurrent and simultaneous inflammationand demyelinationof the optic nerve ( optic neuritis) and the spinal cord ( myelitis). Currently at least two different causes are proposed based on the presence of autoantibodies against AQP4. AQP4+ NMO is currently considered an autoimmune disease(autoimmune astrocytopathy, or autoimmune astrocytic channelopathy) in which a person's own immune systemattacks the astrocytes of the optic nervesand spinal cord. The cause of the AQP4- variants is unknown. 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 weaknessor paralysisin the legs or arms, loss of sensation (including blindness), [ 2 ]and/or bladderand boweldysfunction. [ 3 ] 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. [ 3 ]It has also been suggested to be a variant form of acute disseminated encephalomyelitis. [ 4 ] In AQP+ variants, CNS astrocytes, which are the basis for the glymphatic system [ 5 ]are the target of the autoimmune attack. Symptoms The main symptoms of Devic's disease are loss of visionand spinal cord function. Optic neuritismay manifest as visual impairment with decreased visual acuity, although visual fielddefects, or loss of color visionmay occur in isolation or prior to formal loss of acuity. Spinal cord dysfunction can lead to muscle weakness, reduced sensation, or loss of bladderand bowel control. [ 6 ]The typical patient has an acuteand severe spastic weaknessof the legs ( paraparesis) or all four limbs ( quadriparesis) with sensory signs, often accompanied by loss of bladder control. Mechanism Devic's disease is similar to MS in that the body's immune systemattacks the myelinsurrounding nerve cells. Unlike standard MS, the attacks are not believed to be mediated by the immune system's T cells, but rather by antibodiescalled NMO- IgG, or simply NMO antibodies. These antibodies target the protein aquaporin 4in the cell membranesof astrocyteswhich acts as a channel for the transport of water across the cell membrane. [ 3 ]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 can range from inflammatorydemyelination to necroticdamage of the whiteand grey matters. 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. [ 3 ] [ 7 ] Diagnosis The Mayo Clinicproposed a revised set of criteria for diagnosis of Devic's disease in 2006.