Neuromyelitis optica (NMO) is an inflammatory CNS syndrome distinct from multiple sclerosis (MS) that is associated with serum aquaporin-4 immunoglobulin G antibodies (AQP4-IgG). Prior NMO diagnostic criteria required optic nerve and spinal cord involvement but more restricted or more extensive CNS involvement may occur. The International Panel for NMO Diagnosis (IPND) was convened to develop revised diagnostic criteria using systematic literature reviews and electronic surveys to facilitate consensus. The new nomenclature defines the unifying term NMO spectrum disorders (NMOSD), which is stratified further by serologic testing (NMOSD with or without AQP4-IgG). The core clinical characteristics required for patients with NMOSD with AQP4-IgG include clinical syndromes or MRI findings related to optic nerve, spinal cord, area postrema, other brainstem, diencephalic, or cerebral presentations. More stringent clinical criteria, with additional neuroimaging findings, are required for diagnosis of NMOSD without AQP4-IgG or when serologic testing is unavailable. The IPND also proposed validation strategies and achieved consensus on pediatric NMOSD diagnosis and the concepts of monophasic NMOSD and opticospinal MS.

https://n.neurology.org/content/neurology/85/2/177.full.pdf

International consensus diagnostic criteria for neuromyelitis optica spectrum disorders

Since its discovery in 2007, the encephalitis associated with antibodies against the N-methyl-D-aspartate receptor (NMDAR) has entered the mainstream of neurology and other disciplines. Most patients with anti-NMDAR encephalitis develop a multistage illness that progresses from psychosis, memory deficits, seizures, and language disintegration into a state of unresponsiveness with catatonic features often associated with abnormal movements, and autonomic and breathing instability. The disorder predominantly affects children and young adults, occurs with or without tumour association, and responds to treatment but can relapse. The presence of a tumour (usually an ovarian teratoma) is dependent on age, sex, and ethnicity, being more frequent in women older than 18 years, and slightly more predominant in black women than it is in white women. Patients treated with tumour resection and immunotherapy (corticosteroids, intravenous immunoglobulin, or plasma exchange) respond faster to treatment and less frequently need second-line immunotherapy (cyclophosphamide or rituximab, or both) than do patients without a tumour who receive similar initial immunotherapy. More than 75% of all patients have substantial recovery that occurs in inverse order of symptom development and is associated with a decline of antibody titres. Patients' antibodies cause a titre-dependent, reversible decrease of synaptic NMDAR by a mechanism of crosslinking and internalisation. On the basis of models of pharmacological or genetic disruption of NMDAR, these antibody effects reveal a probable pathogenic relation between the depletion of receptors and the clinical features of anti-NMDAR encephalitis.

https://www.thelancet.com/pdfs/journals/laneur/PIIS1474-4422(10)70253-2.pdf

Clinical experience and laboratory investigations in patients with anti-NMDAR encephalitis

Summary Neuromyelitis optica (also known as Devic's disease) is an idiopathic, severe, demyelinating disease of the central nervous system that preferentially affects the optic nerve and spinal cord. Neuromyelitis optica has a worldwide distribution, poor prognosis, and has long been thought of as a variant of multiple sclerosis; however, clinical, laboratory, immunological, and pathological characteristics that distinguish it from multiple sclerosis are now recognised. The presence of a highly specific serum autoantibody marker (NMO-IgG) further differentiates neuromyelitis optica from multiple sclerosis and has helped to define a neuromyelitis optica spectrum of disorders. NMO-IgG reacts with the water channel aquaporin 4. Data suggest that autoantibodies to aquaporin 4 derived from peripheral B cells cause the activation of complement, inflammatory demyelination, and necrosis that is seen in neuromyelitis optica. The knowledge gained from further assessment of the exact role of NMO-IgG in the pathogenesis of neuromyelitis optica will provide a foundation for rational therapeutic trials for this rapidly disabling disease.

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The spectrum of neuromyelitis optica

The interface between the blood circulation and the neural tissue features unique characteristics that are encompassed by the term 'blood-brain barrier' (BBB). The main functions of this barrier, namely maintenance of brain homeostasis, regulation of influx and efflux transport, and protection from harm, are determined by its specialized multicellular structure. Every constituent cell type makes an indispensable contribution to the BBB's integrity. But if one member of the BBB fails, and as a result the barrier breaks down, there can be dramatic consequences and neuroinflammation and neurodegeneration can occur. In this Review, we highlight recently gained mechanistic insights into the development and maintenance of the BBB. We then discuss how BBB disruption can cause or contribute to neurological disease. Finally, we examine how this knowledge can be used to explore new possibilities for BBB repair.

Development, maintenance and disruption of the blood-brain barrier

Background: There has been tremendous growth in research in pediatric multiple sclerosis (MS) and immune mediated central nervous system demyelinating disorders since operational definitions for these conditions were first proposed in 2007. Further, the International Pediatric Multiple Sclerosis Study Group (IPMSSG), which proposed the criteria, has expanded substantially in membership and in its international scope. Objective: The purpose of this review is to revise the 2007 definitions in order to incorporate advances in delineating the clinical and neuroradiologic features of these disorders. Methods: Through a consensus process, in which input was sought from the 150 members of the Study Group, criteria were drafted, revised and finalized. Final approval was sought through a web survey. Results: Revised criteria are proposed for pediatric acute disseminated encephalomyelitis, pediatric clinically isolated syndrome, pediatric neuromyelitis optica and pediatric MS. These criteria were approved by 93% or more of the 56 Study Group members who responded to the final survey. Conclusions: These definitions are proposed for clinical and research purposes. Their utility will depend on the outcomes of their application in prospective research.

International Pediatric Multiple Sclerosis Study Group criteria for pediatric multiple sclerosis and immune-mediated central nervous system demyelinating disorders: revisions to the 2007 definitions

Objectives: Neuromyelitis optica (NMO) immunoglobulin G (IgG) (aquaporin-4 [AQP4] IgG) is highly specific for NMO and related disorders, and autoantibody detection has become an essential investigation in patients with demyelinating disease. However, although different techniques are now used, no multicenter comparisons have been performed. This study compares the sensitivity and specificity of different assays, including an in-house flow cytometric assay and 2 commercial assays (ELISA and transfected cell-based assay [CBA]). Methods: Six assay methods (in-house or commercial) were performed in 2 international centers using coded serum from patients with NMO (35 patients), NMO spectrum disorders (25 patients), relapsing-remitting multiple sclerosis (39 patients), miscellaneous autoimmune diseases (25 patients), and healthy subjects (22 subjects). Results: The highest sensitivities were yielded by assays detecting IgG binding to cells expressing recombinant AQP4 with quantitative flow cytometry (77; 46 of 60) or visual observation (CBA, 73%; 44 of 60). The fluorescence immunoprecipitation assay and tissue-based immunofluorescence assay were least sensitive (48%–53%). The CBA and ELISA commercial assays (100% specific) yielded sensitivities of 68% (41 of 60) and 60% (36 of 60), respectively, and sensitivity of 72% (43 of 60) when used in combination. Conclusions: The greater sensitivity and excellent specificity of second-generation recombinant antigen-based assays for detection of NMO-IgG in a clinical setting should enable earlier diagnosis of NMO spectrum disorders and prompt initiation of disease-appropriate therapies.

/pdf/serologic-diagnosis-of-nmo-a-multicenter-comparison-of-3qgw3cople.pdf

Serologic diagnosis of NMO: A multicenter comparison of aquaporin-4-IgG assays

Background: Autoantibody specific for the aquaporin-4 astrocytic water channel is restricted to serum and CSF of patients with neuromyelitis optica (NMO) and related CNS inflammatory demyelinating disorders (relapsing optic neuritis and longitudinally extensive transverse myelitis). NMO-typical lesions are distinct from MS-typical lesions. Aquaporin-4 is lost selectively at vasculocentric sites of edema/inflammation coinciding with focal deposits of immunoglobulins (Ig) G, M, and terminal complement products, with and without myelin loss. Evidence for antigen-specific autoantibody pathogenicity is lacking. Methods: We used confocal microscopy and flow cytometry to evaluate the selectivity and immunopathological consequences of Ig binding to surface epitopes of living target cells expressing aquaporin-4 fused at its cytoplasmic N-terminus with GFP. We tested serum, IgG-enriched and IgG-depleted serum fractions, and CSF from patients with NMO, neurologic control patients, and healthy subjects. We also analyzed aquaporin-4 immunoreactivity in myelinated adult mouse optic nerves and spinal cord, and plasma cell Ig isotypes in archived brain tissue from an NMO patient. Results: Serum IgG from patients with NMO binds to the extracellular domain of aquaporin-4; it is predominantly IgG 1 , and it initiates two potentially competing outcomes, aquaporin-4 endocytosis/degradation and complement activation. Serum and CSF lack aquaporin-4-specific IgM, and plasma cells in CNS lesions of NMO contain only IgG. Paranodal astrocytic endfeet highly express aquaporin-4. Conclusions: NMO patients’ serum IgG has a selective pathologic effect on cell membranes expressing aquaporin-4. IgG targeting astrocytic processes around nodes of Ranvier could initiate demyelination.

Pathogenic potential of IgG binding to water channel extracellular domain in neuromyelitis optica

Objective: To determine the prognostic value of neuromyelitis optica (NMO)–immunoglobulin G (IgG) in patients with recurrent optic neuritis (ON). The aquaporin-4-specific serum autoantibody, NMO-IgG, is a biomarker for NMO and relapsing transverse myelitis. Recurrent ON may herald multiple sclerosis (MS) or NMO, or it may occur as an isolated syndrome. The prognosis and response to therapy differs in each of these contexts. Methods: We evaluated 34 patients who were tested for NMO-IgG between 2000 and 2007 and who had two or more episodes of ON without satisfying a diagnosis of MS or NMO prior to serologic testing. Clinical data were available for 25 Mayo Clinic patients (5 NMO-IgG positive and 20 NMO-IgG negative) and for an additional 9 seropositive patients whose serum was referred to the Mayo Clinic Neuroimmunology laboratory for testing. Results: Twenty percent of the patients with recurrent ON seen at Mayo Clinic were seropositive. All NMO-IgG-positive patients (vs 65% NMO-IgG-negative patients) had at least one attack with visual acuity in the affected eye worse than 20/200 (p = 0.05). In seropositive patients for whom long-term follow-up was possible (median 8.9 years after the initial ON), 6 of 12 (50%) experienced an episode of myelitis and fulfilled criteria for NMO. In contrast, 1 of 15 seronegative patients (6.7%) fulfilled McDonald criteria for MS (p = 0.03). Seropositive patients had a final visual score which was worse than that of seronegative patients (p = 0.02). Conclusions: Neuromyelitis optica (NMO)–immunoglobulin G seropositivity predicts poor visual outcome and development of NMO. Seropositive recurrent optic neuritis is a limited form of NMO.

NMO-IgG predicts the outcome of recurrent optic neuritis

We compared the clinical course of 96 patients with neuromyelitis optica (NMO) to multiple sclerosis (MS) natural history data. Based on the distribution of follow-up data (median 6.1 year), we estimated that 21 NMO patients would convert to a secondary progressive course, but we observed only two conversions (p = 0.00002; relative risk = 0.08). The disparate natural histories of MS and NMO suggest dissociation between relapses and clinical progression in CNS demyelinating diseases.

A secondary progressive clinical course is uncommon in neuromyelitis optica

Objective: To characterize the neuropathologic features of neuromyelitis optica (NMO) at the medullary floor of the fourth ventricle and area postrema. Aquaporin-4 (AQP4) autoimmunity targets this region, resulting in intractable nausea associated with vomiting or hiccups in NMO. Methods: This neuropathologic study was performed on archival brainstem tissue from 15 patients with NMO, 5 patients with multiple sclerosis (MS), and 8 neurologically normal subjects. Logistic regression was used to evaluate whether the presence of lesions at this level increased the odds of a patient with NMO having an episode of nausea/vomiting. Results: Six patients with NMO (40%), but no patients with MS or normal controls, exhibited unilateral or bilateral lesions involving the area postrema and the medullary floor of the fourth ventricle. These lesions were characterized by tissue rarefaction, blood vessel thickening, no obvious neuronal or axonal pathology, and preservation of myelin in the subependymal medullary tegmentum. AQP4 immunoreactivity was lost or markedly reduced in all 6 cases, with moderate to marked perivascular and parenchymal lymphocytic inflammatory infiltrates, prominent microglial activation, and in 3 cases, eosinophils. Complement deposition in astrocytes, macrophages, and/or perivascularly, and a prominent astroglial reaction were also present. The odds of nausea/vomiting being documented clinically was 16-fold greater in NMO cases with area postrema lesions (95% confidence interval 1.43–437, p = 0.02). Conclusions: These neuropathologic findings suggest the area postrema may be a selective target of the disease process in NMO, and are compatible with clinical reports of nausea and vomiting preceding episodes of optic neuritis and transverse myelitis or being the heralding symptom of NMO.

Sean J. Pittock

Papers

Serologic diagnosis of NMO: A multicenter comparison of aquaporin-4-IgG assays

Pathogenic potential of IgG binding to water channel extracellular domain in neuromyelitis optica

NMO-IgG predicts the outcome of recurrent optic neuritis

A secondary progressive clinical course is uncommon in neuromyelitis optica

Neuromyelitis optica unique area postrema lesions: Nausea, vomiting, and pathogenic implications