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

High-throughput flow cytometry cell-based assay to detect antibodies to N-methyl-D-aspartate receptor or dopamine-2 receptor in human serum

Over the recent years, antibodies against surface and conformational proteins involved in neurotransmission have been detected in autoimmune CNS diseases in children and adults. These antibodies have been used to guide diagnosis and treatment. Cell-based assays have improved the detection of antibodies in patient serum. They are based on the surface expression of brain antigens on eukaryotic cells, which are then incubated with diluted patient sera followed by fluorochrome-conjugated secondary antibodies. After washing, secondary antibody binding is then analyzed by flow cytometry. Our group has developed a high-throughput flow cytometry live cell-based assay to reliably detect antibodies against specific neurotransmitter receptors. This flow cytometry method is straight forward, quantitative, efficient, and the use of a high-throughput sampler system allows for large patient cohorts to be easily assayed in a short space of time. Additionally, this cell-based assay can be easily adapted to detect antibodies to many different antigenic targets, both from the central nervous system and periphery. Discovering additional novel antibody biomarkers will enable prompt and accurate diagnosis and improve treatment of immune-mediated disorders.

Aquaporin-4 autoantibodies in Neuromyelitis Optica: AQP4 isoform-dependent sensitivity and specificity

Neuromyelitis Optica (NMO) is an autoimmune demyelinating disease, characterized by the presence of autoantibody (NMO-IgG) to Aquaporin-4 (AQP4). NMO-IgG identification supports NMO diagnosis and several diagnostic tests have been developed, but their sensitivity is too variable, and some assay show low sensitivity. This impairs correct diagnosis of NMO. By cell based assay (CBA) we here evaluate the efficacy of different strategies to express AQP4 in mammalian cells in terms of: a) AQP4 translation initiation signals; b) AQP4 isoforms (M1 and M23) and fluorescent tag position; c) NMO serum concentration and AQP4 degradation. Our results demonstrate that when using AQP4-M1, the nucleotide in position -3 of the AUG greatly affects the AQP4-M1/M23 protein ratio, NMO-IgG binding, and consequently test sensitivity. Test sensitivity was highest with M23 expressing cells (97.5%) and only 27.5% with AQP4-M1. The fluorescent tag added to the N-terminus of AQP4-M23 considerably affected the NMO-IgG binding, and test sensitivity, due to disruption of AQP4 suprastructures. Furthermore, sera used at high concentration resulted in AQP4 degradation which affected test sensitivity. To further evaluate the reliability of the M23 based CBA test, samples of one NMO patient collected during about 2 years clinical follow-up were tested. The results of serum titer correlated with disease activity and treatment response. In conclusion, we provide a molecular explanation for the contrasting CBA test data reported and suggest the use of M23 with a C-terminus fluorescent tag as the proper test for NMO diagnosis.

Contribution of spinal cord biopsy to diagnosis of aquaporin-4 antibody positive neuromyelitis optica spectrum disorder

Longitudinally extensive transverse myelitis is characteristic but not pathognomonic for neuromyelitis optica spectrum disorders (NMOSDs) and may mimic local tumors. In this retrospective study based on a cohort of 175 NMOSD patients we identified seven patients who initially presented with a longitudinally extensive spinal cord lesion and underwent spinal cord biopsy due to magnetic resonance imaging (MRI)-suspected malignancies. Remarkably, routine neuropathology was inconclusive and did not guide the diagnostic process to anti-aquaporin-4 (AQP4)-seropositive NMOSD. Serious postoperative complications occurred in 5/7 patients and persisted during follow-up in 2/7 patients (29%). Considering these sequelae, AQP4-antibody testing should be mandatory in patients with inconclusive longitudinally extensive spinal cord lesions prior to biopsy.

An optimized immunohistochemistry technique improves NMO-IgG detection: study comparison with cell-based assays

Cell-based assays (CBA) have increased the sensitivity of the neuromyelitis optica (NMO)-IgG/aquaporin-4-antibody detection compared to classical tissue-based indirect assays. We describe the sensitivity of an optimized immunohistochemistry (IHC-o) to detect NMO-IgG/aquaporin-4-antibody in comparison with that of two CBA: an in-house (CBA-ih) and a commercial (CBA-c) assay (Euroimmun, Germany). Coded serum from 103 patients with definite NMO and 122 inflammatory controls were studied by IHC-o, CBA-ih, and CBA-c. IHC-o used the same protocol described to detect antibodies against cell surface antigens. CBA-ih used live cells transfected with the aquaporin-4-M23-isoform. The sensitivity of the IHC-o was 74.8% (95% confidence interval [CI] 65-83) and was similar to that of the CBA-ih 75.7% (95% CI 66-84) and the CBA-c 73.8% (95% CI 64-82). The specificity of the three assays was 100% (95% CI 97-100). Interassay concordance was high, 100 of 103 samples were coincident in all techniques. The optimized immunohistochemistry proves to be as sensitive and specific as the cell-based assays. This assay extends the available tools for NMO-IgG/aquaporin-4-antibody detection.

Aquaporin-4 antibodies (NMO-IgG) as a serological marker of neuromyelitis optica: a critical review of the literature

Antibodies to aquaporin-4 (called NMO-IgG or AQP4-Ab) constitute a sensitive and highly specific serum marker of neuromyelitis optica (NMO) that can facilitate the differential diagnosis of NMO and classic multiple sclerosis. NMO-IgG/AQP4-Ab seropositive status has also important prognostic and therapeutic implications in patients with isolated longitudinally extensive myelitis (LETM) or optic neuritis (ON). In this article, we comprehensively review and critically appraise the existing literature on NMO-IgG/AQP4-Ab testing. All available immunoassays-including tissue-based (IHC), cell-based (ICC, FACS) and protein-based (RIPA, FIPA, ELISA, Western blotting) assays-and their differential advantages and disadvantages are discussed. Estimates for sensitivity, specificity, and positive and negative likelihood ratios are calculated for all published studies and accuracies of the various immunoassay techniques compared. Subgroup analyses are provided for NMO, LETM and ON, for relapsing vs. monophasic disease, and for various control groups (eg, MS vs. other controls). Numerous aspects of NMO-IgG/AQP4-Ab testing relevant for clinicians (eg, impact of antibody titers and longitudinal testing, indications for repeat testing, relevance of CSF testing and subclass analysis, NMO-IgG/AQP4-Ab in patients with rheumatic diseases) as well as technical aspects (eg, AQP4-M1 vs. AQP4-M23-based assays, intact AQP4 vs. peptide substrates, effect of storage conditions and freeze/thaw cycles) and pitfalls are discussed. Finally, recommendations for the clinical application of NMO-IgG/AQP4-Ab serology are given.

Neuromyelitis optica-IgG testing in an Indian cohort with neuromyelitis optica and related demyelinating disorders: Our experience

BACKGROUND

Neuromyelitis optica (NMO) is an immune-mediated inflammatory demyelinating disorder of the central nervous system with a predilection for the optic nerves and the spinal cord. Immunopathological evidence suggests that the target antigen of the disease is aquaporin-4. An IgG antibody against this protein has been explored as a molecular marker for the disease and as a diagnostic tool due to its high sensitivity and specificity in various populations.

OBJECTIVE

To assess the value of NMO-IgG testing in Indian patients with clinical and magnetic resonance imaging features consistent with NMO and longitudinally extensive transverse myelitis (LETM).

MATERIALS AND METHODS

Forty-five patients with clinical and magnetic resonance imaging features consistent with NMO, LETM, and MS were tested for serum NMO-IgG. Of these patients, 22 patients satisfied revised (2006) Wingerchuk criteria for NMO (excluding NMO-IgG status) and 11 patients had LETM. Twelve patients satisfied the revised (2010) McDonald criteria for multiple sclerosis (MS).

RESULTS

Of the 21 patients, satisfying the criteria for NMO and for whom the test results were available, 17 were positive for NMO-IgG (80.9%), and of the 11 patients having LETM, 6 (54.5%) were positive for NMO-IgG. In one patient with NMO, the test result was not available. None of the 12 patients satisfying McDonald criteria for MS showed NMO-IgG seropositivity.

CONCLUSION

Our study suggests that it is worthwhile to pursue NMO-IgG testing as a diagnostic tool for patients with clinical and Magnetic Resonance Imaging (MRI) features consistent with NMO and LETM in the Indian population.

Anti-aquaporin-1 autoantibodies in patients with neuromyelitis optica spectrum disorders

Autoantibodies against aquaporin-4 (AQP4), a water channel in CNS astrocytes, are detected in ∼50–80% of patients with neuromyelitis optica spectrum disorders (NMOsd), characterized by longitudinally extensive transverse myelitis (LETM) and/or optic neuritis. Although these autoantibodies present an invaluable biomarker for NMOsd and for the differential diagnosis of multiple sclerosis (MS), diagnosis of anti-AQP4-seronegative NMOsd remains challenging. We hypothesized that seronegative NMOsd patients might have autoantibodies against aquaporin-1 (AQP1), another water channel in CNS astrocytes. We initially developed a radioimmunoprecipitation assay to search for anti-AQP1 antibodies in sera from 632 individuals. Anti-AQP1 or anti-AQP4 autoantibodies were detected in 16.7% and 12%, respectively, of 348 patients with suspected NMOsd. Anti-AQP1 specificity was confirmed by competition, protein immunoblotting and ELISA assays, whereas epitope localization was studied by immunoadsorption on intact cells expressing AQP1 and peptide mapping experiments. Most anti-AQP1 autoantibodies were of the complement-activating IgG1 subclass and the majority bound to the extracellular domain of AQP1, suggesting a possible pathogenic role. Five out of 42 MS patients had anti-AQP1 antibodies, but 2 of them also had spinal cord lesions, while the anti-AQP1 antibodies in the other 3 bound to the cytoplasmic domain of AQP1. Anti-AQP1 antibodies were not detected in 100 healthy individuals or 142 patients with non-demyelinating neuroimmune diseases. Analysis of 17 anti-AQP1+/anti-AQP4- patients with suspected NMOsd showed that 5 had NMO and 11 had LETM. 12/17 of these sera bound predominantly to the extracellular AQP1 loop-Α. Overall, we found that anti-AQP1 autoantibodies are present in a subgroup of patients with chronic demyelination in the CNS and similarities with anti-AQP4-seronegative NMOsd, offering a novel potential biomarker for CNS demyelination disorders.

Optic neuritis in neuromyelitis optica

Neuromyelitis optica (NMO) is an autoimmune demyelinating disease associated with recurrent episodes of optic neuritis and transverse myelitis, often resulting in permanent blindness and/or paralysis. The discovery of autoantibodies (AQP4-IgG) that target aquaporin-4 (AQP4) has accelerated our understanding of the cellular mechanisms driving NMO pathogenesis. AQP4 is a bidirectional water channel expressed on the plasma membranes of astrocytes, retinal Müller cells, skeletal muscle, and some epithelial cells in kidney, lung and the gastrointestinal tract. AQP4 tetramers form regular supramolecular assemblies at the cell plasma membrane called orthogonal arrays of particles. The pathological features of NMO include perivascular deposition of immunoglobulin and activated complement, loss of astrocytic AQP4, inflammatory infiltration with granulocyte and macrophage accumulation, and demyelination with axon loss. Current evidence supports a causative role of AQP4-IgG in NMO, in which binding of AQP4-IgG to AQP4 orthogonal arrays on astrocytes initiates complement-dependent and antibody-dependent cell-mediated cytotoxicity and inflammation. Immunosuppression and plasma exchange are the mainstays of therapy for NMO optic neuritis. Novel therapeutics targeting specific steps in NMO pathogenesis are entering the development pipeline, including blockers of AQP4-IgG binding to AQP4 and inhibitors of granulocyte function. However, much work remains in understanding the unique susceptibility of the optic nerves in NMO, in developing animal models of NMO optic neuritis, and in improving therapies to preserve vision.

Updated estimate of AQP4-IgG serostatus and disability outcome in neuromyelitis optica

OBJECTIVE

To 1) determine, using contemporary recombinant antigen-based assays, the aquaporin-4 (AQP4)-immunoglobulin G (IgG) detection rate in sequential sera of patients assigned a clinical diagnosis of neuromyelitis optica (NMO) but initially scored negative by tissue-based indirect immunofluorescence (IIF) assay; and 2) evaluate the impact of serostatus on phenotype and outcome.

METHODS

From Mayo Clinic records (2005-2011), we identified 163 patients with NMO; 110 (67%) were seropositive by IIF and 53 (33%) were scored seronegative. Available stored sera from 49 "seronegative" patients were tested by ELISA, AQP4-transfected cell-based assay, and in-house fluorescence-activated cell sorting assay. Clinical characteristics were compared based on final serostatus.

RESULTS

Thirty of the 49 IIF-negative patients (61%) were reclassified as seropositive, yielding an overall AQP4-IgG seropositivity rate of 88% (i.e., 12% seronegative). The fluorescence-activated cell sorting assay improved the detection rate to 87%, cell-based assay to 84%, and ELISA to 79%. The sex ratio (female to male) was 1:1 for seronegatives and 9:1 for seropositives (p < 0.0001). Simultaneous optic neuritis and transverse myelitis as onset attack type (i.e., within 30 days of each other) occurred in 32% of seronegatives and in 3.6% of seropositives (p < 0.0001). Relapse rate, disability outcome, and other clinical characteristics did not differ significantly.

CONCLUSIONS

Serological tests using recombinant AQP4 antigen are significantly more sensitive than tissue-based IIF for detecting AQP4-IgG. Testing should precede immunotherapy; if negative, later-drawn specimens should be tested. AQP4-IgG-seronegative NMO is less frequent than previously reported and is clinically similar to AQP4-IgG-seropositive NMO.

Paraneoplastic and other autoimmune disorders of the central nervous system

As a result of the burgeoning growth of disease-specific neural autoantibody markers available for diagnostic patient evaluation, there has been increasing awareness of autoimmune central nervous system (CNS) disorders in hospital practice. Hospital-based neurologists have also taken great interest in these disorders since many occur in the setting of an occult systemic cancer which can be detected and treated at an early stage, and many affected patients are responsive to immunotherapy. Associated neurological disorders are typically subacute in onset, some are common or classic (eg, limbic encephalitis, cerebellar degeneration), but others have atypical or multifocal presentations. For patients with a suspected paraneoplastic disorder, many and costly oncological evaluations may be required for diagnosis. Comprehensive serological and cerebrospinal fluid (CSF) evaluation for neural autoantibodies may permit a focused cancer evaluation (eg, antineuronal nuclear antibody type 1 [ANNA-1] is associated with small cell lung carcinoma), and in some circumstances may indicate the likelihood of a good response to therapy (eg, voltage-gated potassium channel complex antibody) or poor neurological prognosis (eg, purkinje cell cytoplasmic antibody type 1 [antiYo]). Positron-emission tomography-computed tomography (PET-CT) imaging of trunk may increase the diagnostic yield for certain cancers where other modalities have been negative. For some patients, rapid treatment with immunotherapy may facilitate marked improvement, or full recovery; multiple sequential trials of one or more of steroids, intravenous immunoglobulin or plasma exchange, or combination therapy are often required. For patients with N-methyl-d-aspartate receptor antibody encephalitis, early treatment with immunosuppressants and weeks or months of supportive intensive care may additionally be required. One or more of clinical examination, electroencephalogram (including video telemetry), and imaging provide objective parameters to which posttreatment outcomes can be compared.

Autoantibodies and the immune hypothesis in psychotic brain diseases: challenges and perspectives

The pathophysiology of psychosis is poorly understood, with both the cognitive and cellular changes of the disease process remaining mysterious. There is a growing body of evidence that points to dysfunction of the immune system in a subgroup of patients with psychosis. Recently, autoantibodies directed against neuronal cell surface targets have been identified in a range of syndromes that feature psychosis. Of interest is the detection of autoantibodies in patients whose presentations are purely psychiatric, such as those suffering from schizophrenia. Autoantibodies have been identified in a minority of patients, suggesting that antibody-associated mechanisms of psychiatric disease likely only account for a subgroup of cases. Recent work has been based on the application of cell-based assays-a paradigm whose strength lies in the expression of putative antigens in their natural conformation on the surface of live cells. The responsiveness of some of these newly described clinical syndromes to immune therapy supports the hypothesis that antibody-associated mechanisms play a role in the pathogenesis of psychotic disease. However, further investigation is required to establish the scope and significance of antibody pathology in psychosis. The identification of a subgroup of patients with antibody-mediated disease would promise more effective approaches to the treatment of these high-morbidity conditions.

Neuromyelitis optica IgG causes placental inflammation and fetal death

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease of the CNS and affects women of childbearing age. Most patients with NMO have circulating Abs, termed NMO-IgG, against the astrocytic water channel protein aquaporin-4. In the CNS, NMO-IgG causes complement-mediated astrocyte damage, inflammatory cell infiltration, and myelin loss. In this study, we show that aquaporin-4 is expressed in the syncytiotrophoblast of human and mouse placenta. Placental aquaporin-4 expression is high during mid-gestation and progressively decreases with advancing pregnancy. Intraperitoneally injected NMO-IgG binds mouse placental aquaporin-4, activates coinjected human complement, and causes inflammatory cell infiltration into the placenta and placental necrosis. There was no damage to maternal organs that express aquaporin-4, including the brain, spinal cord, kidneys, and skeletal muscle. In control experiments, no placentitis was found in mice injected with NMO-IgG without complement, non-NMO-IgG with human complement, or in aquaporin-4 null mice injected with NMO-IgG and human complement. The infiltrating cells were primarily neutrophils with a few scattered eosinophils and macrophages. NMO-IgG and human complement-induced placentitis caused fetal death, but some fetuses were born normal when lower amounts of NMO-IgG and human complement were injected. Sivelestat, a neutrophil elastase inhibitor, and aquaporumab, a nonpathogenic IgG that competes with NMO-IgG for aquaporin-4 binding, significantly reduced NMO-IgG and human complement induced placentitis and fetal death. Our data suggest that NMO-IgG can cause miscarriage, thus challenging the concept that NMO affects only the CNS. These findings have implications for the management of NMO during pregnancy.

Current concept of neuromyelitis optica (NMO) and NMO spectrum disorders

Neuromyelitis optica (NMO) has been described as a disease clinically characterised by severe optic neuritis (ON) and transverse myelitis (TM). Other features of NMO include female preponderance, longitudinally extensive spinal cord lesions (>3 vertebral segments), and absence of oligoclonal IgG bands . In spite of these differences from multiple sclerosis (MS), the relationship between NMO and MS has long been controversial. However, since the discovery of NMO-IgG or aquaporin-4 (AQP4) antibody (AQP4-antibody), an NMO-specific autoantibody to AQP4, the dominant water channel in the central nervous system densely expressed on end-feet of astrocytes, unique clinical features, MRI and other laboratory findings in NMO have been clarified further. AQP4-antibody is now the most important laboratory finding for the diagnosis of NMO. Apart from NMO, some patients with recurrent ON or recurrent longitudinally extensive myelitis alone are also often positive for AQP4-antibody. Moreover, studies of AQP4-antibody-positive patients have revealed that brain lesions are not uncommon in NMO, and some patterns appear to be unique to NMO. Thus, the spectrum of NMO is wider than mere ON and TM. Pathological analyses of autopsied cases strongly suggest that unlike MS, astrocytic damage is the primary pathology in NMO, and experimental studies confirm the pathogenicity of AQP4-antibody. Importantly, therapeutic outcomes of some immunological treatments are different between NMO and MS, making early differential diagnosis of these two disorders crucial. We provide an overview of the epidemiology, clinical and neuroimaging features, immunopathology and therapy of NMO and NMO spectrum disorders.

NMO spectrum disorders comprise the major portion of CNS inflammatory diseases in Thai patients: A cross sectional study

BACKGROUND

Neuromyelitis optica (NMO) is more prevalent than multiple sclerosis (MS) in the Asian population. AQP4-IgG as a specific biomarker for NMO has not been systematically validated in Thai patients.

OBJECTIVE

To identify the proportion of central nervous system demyelinating disease of Thai patient in one of referral center and examine its clinico-serological correlation with AQP4-IgG status.

METHOD

Cross sectional collected sera from patients who visited or were admitted to Prasat Neurological Institute from November 2009 to August 2010 were tested for serum AQP4-IgG levels. Patient information was reviewed and diagnoses of MS and clinical isolated syndrome (CIS) were made using the Revised McDonald criteria 2005. Diagnosis of NMO was made using the Revised NMO criteria 2006 (except for AQP4-IgG status) and NMO spectrum disorder (NMOSD) criteria 2007.

RESULTS

Sixty-one patients were identified including 12 with NMO, 25 with limited form of NMO, 16 with relapsing remitting MS (RRMS), and 8 with CIS. AQP4-IgG was found in 65% of patients in the NMOSD group. In the MS/CIS group, 2 were AQP4-IgG seropositive. Pleocytosis was significantly higher in the NMOSD group than the MS/CIS group. Cranial MRI revealed that the size and degree of brain lesions were similar in all study groups. However, spinal MRI showed that the MS/CIS groups had a higher prevalence of short segment myelitis and a higher abundance of white matter (p<0.05) than NMOSD group. AQP4-IgG seropositive samples correlated with female patients and the presence of optic neuritis.

CONCLUSION

NMOSD is more common than MS in Thai patients. Moreover, AQP4-IgG is highly specific for NMOSD. Spinal MRI can effectively distinguish NMOSD from MS patients. AQP4-IgG seropositivity is highly correlated with females and the presence of optic neuritis.

Neuroradiological evaluation of demyelinating disease

Central nervous system inflammatory demyelinating disease can affect patients across the life span. Consensus definitions and criteria of all of the different acquired demyelinating diseases that fall on this spectrum have magnetic resonance imaging criteria. The advances of both neuroimaging techniques and important discoveries in immunology have produced an improved understanding of these conditions and classification. Neuroimaging plays a central role in the accurate diagnosis, prognosis, disease monitoring and research efforts that are being undertaken in this disease. This review focuses on the imaging spectrum of acquired demyelinating disease.

Central nervous system inflammatory demyelinating disorders among Hong Kong Chinese

Classical multiple sclerosis (CMS) and neuromyelitis optica spectrum disorders (NMOSD) are distinct central nervous system inflammatory demyelinating disorders (CNS IDD). Early diagnosis of CNS IDD is important as appropriate immunotherapies to optimize prognosis. We studied the diagnoses of CNS IDD among Hong Kong Chinese in a hospital-based setting. Consecutive Chinese patients who presented to our hospital with clinically isolated syndrome and subsequently diagnosed to have CNS IDD from 1980 to 2010 were reviewed. Patients with known diagnosis of CNS IDD referred for further care were excluded. Serial sera were assayed for aquaporin-4 autoantibodies (AQP4 Ab), at least 3 assays within 2-5years. A total of 210 patients diagnosed to have CNS IDD with disease duration of at least 2years were studied. Among 198 patients with serial sera available, 40 (20.2%, 20 had NMO and 20 other NMOSD) were AQP4 Ab-positive. Four patients who were AQP4 Ab-negative on the initial assay converted to AQP4 Ab-positive on repeated assays. The diagnoses of 210 patients were CMS in 88 (41.9%), NMOSD 47 (22.4%, 27 NMO, 20 other NMOSD), single attack of myelitis 23 (11.0%), single attack of optic neuritis 21 (10.0%), relapsing myelitis 10 (4.8%), acute disseminated encephalomyelitis (ADEM) 9 (4.3%), relapsing optic neuritis in 6 (2.9%), opticospinal multiple sclerosis 3 (1.4%) and single attack of brainstem encephalitis 3 (1.4%). Compared to CMS, NMOSD patients had older onset age, lower frequencies of brain MRI abnormalities and CSF OCB, higher frequency of LETM, higher CNS inflammation attack frequency in the first 2years, worse clinical outcome with higher EDSS score and mortality rate. This hospital-based study suggests that CMS (41.9%) and NMOSD (22.4%) are the most common CNS IDD among Hong Kong Chinese. NMOSD has worse clinical outcome than CMS. Detection of AQP4 Ab facilitates early diagnosis and prompts immunotherapies of NMOSD.

The spectrum of MOG autoantibody-associated demyelinating diseases

Myelin oligodendrocyte glycoprotein (MOG) has been identified as a target of demyelinating autoantibodies in animal models of inflammatory demyelinating diseases of the CNS, such as multiple sclerosis (MS). Numerous studies have aimed to establish a role for MOG antibodies in patients with MS, although the results have been controversial. Cell-based immunoassays using MOG expressed in mammalian cells have demonstrated the presence of high-titre MOG antibodies in paediatric patients with acute disseminated encephalomyelitis, MS, aquaporin-4-seronegative neuromyelitis optica, or isolated optic neuritis or transverse myelitis, but only rarely in adults with these disorders. These studies indicate that MOG antibodies could be associated with a broad spectrum of acquired human CNS demyelinating diseases. This Review article discusses the current literature on MOG antibodies, their potential clinical relevance, and their role in the pathogenesis of MOG antibody-associated demyelinating disorders.

Distinctive clinical and neuroimaging characteristics of longitudinally extensive transverse myelitis associated with aquaporin-4 autoantibodies

Longitudinally extensive transverse myelitis (LETM) is a characteristic feature of Neuromyelitis Optica (NMO), but it can also occur in several other inflammatory diseases of the central nervous system (CNS). An IgG autoantibody that binds to aquaporin-4 (AQP4), the predominant water channel of the CNS, is a reliable biomarker of the NMO spectrum disorders, and if detected predicts the recurrence of the myelitis. In this study, we compared the clinical and neuroimaging characteristics of AQP4-IgG+ and AQP4-IgG- LETM patients. Thirty-seven first-ever LETM patients were retrospectively evaluated and divided into two groups according to the presence of AQP4 autoantibodies. AQP4-IgG was detected in the serum and in the cerebrospinal fluid of sixteen patients. The female to male ratio was higher in AQP4-IgG+ patients. Intractable nausea and vomiting and paroxysmal tonic spasms often accompanied the LETM in AQP4-IgG+ patients. T2-weighted spinal cord MRI revealed that inflammatory lesions extending into the brainstem and involving the central grey matter occurred more frequently in AQP4-IgG+ LETM patients. Hypointense lesions on T1-weighted spinal cord MRI were detected more frequently in the seropositive group, and their presence correlated with attack severity. In conclusion, this study provides clinical and spinal cord neuroimaging clues that can help distinguishing AQP4-IgG+ LETM patients.

Chronic relapsing inflammatory optic neuropathy: a systematic review of 122 cases reported

Chronic relapsing inflammatory optic neuropathy (CRION) is an entity that was described in 2003. Early recognition of patients suffering from CRION is relevant because of the associated risk for blindness if treated inappropriately. It seems timely to have a clinical review on this recently defined entity. A systematic literature review, irrespective of language, retrieved 22 case series and single reports describing 122 patients with CRION between 2003 and 2013. We review the epidemiology, diagnostic workup, differential diagnosis, and treatment (acute, intermediate, and long term) in view of the collective data. These data suggest that CRION is a distinct nosological entity, which is seronegative for anti-aquaporin four auto-antibodies and recognized by and managed through its dependency on immuno-suppression. Revised diagnostic criteria are proposed in light of the data compromising a critical discussion of relevant limitations.

Antibodies identified by cell-based assays in myasthenia gravis and associated diseases

We have established cell-based assays for the improved detection of acetylcholine receptor (AChR) and muscle-specific kinase (MuSK) antibodies in myasthenia gravis. This approach has enabled us to demonstrate antibodies to "clustered" AChRs in patients who were previously AChR antibody negative and can also be used to distinguish between adult and fetal AChR antibodies in mothers of babies with arthrogryposis multiplex congenita. We summarize our recent evidence for the pathogenicity of MuSK and clustered AChR antibodies using in vivo models. Cell-based assays are now also being used for the detection of other antibodies, such as those directed to components of the VGKC/CASPR2/LGI1 complex in Morvan's syndrome, and to AQP4 antibodies in neuromyelitis optica; both of these diseases can be associated with MG and sometimes thymoma. The cell-based method is time consuming but has many advantages and may provide a gold standard for the future in the detection of pathogenic autoantibodies in patients with immune-mediated diseases.

Discovery of peptoid ligands for anti-aquaporin 4 antibodies

Neuromyelitis optica (NMO) is an autoimmune inflammatory disorder of the central nervous system. In most NMO patients, autoantibodies to the water channel protein Aquaporin 4 (AQP4) are present at high levels and are thought to drive pathology by mediating complement-dependent destruction of astrocytes. Here, we apply recently developed chemical library screening technology to identify a synthetic peptoid that binds anti-AQP4 antibodies in the serum of NMO patients. This finding validates, in a well-defined human disease, that synthetic, unnatural ligands for the antigen-binding site of a disease-linked antibody can be isolated by high-throughput screening.

In vivo identification of morphologic retinal abnormalities in neuromyelitis optica

OBJECTIVE

To assess eyes with neuromyelitis optica (NMO) for morphologic retinal abnormalities utilizing high-definition optical coherence tomography (OCT) imaging.

METHODS

In this cross-sectional study, 39 patients with NMO spectrum disorders and 39 age- and sex-matched healthy controls underwent spectral-domain OCT and visual function testing.

RESULTS

Microcystic macular edema (MME) of the inner nuclear layer (INL) was identified in 10 of 39 patients (26%) and was exclusively found in eyes with a history of optic neuritis (ON). MME eyes had lower high- and low-contrast letter-acuity scores (100%: p = 0.002; 2.5%: p = 0.002; 1.25%: p = 0.004), lower peripapillary retinal nerve fiber layer (RNFL) thickness (p = 0.04), lower macular RNFL thickness (p = 0.004), lower ganglion cell layer + inner plexiform layer (GCIP) thickness (p = 0.007), higher INL thickness (p < 0.001), and a greater number of ON episodes (p = 0.008) relative to non-MME eyes with a history of ON. After adjusting for history of multiple ON episodes, these findings remained significant for macular-RNFL thickness (p = 0.03), INL thickness (p < 0.001), and 100% and 2.5% contrast letter-acuity scores (p = 0.008 and p = 0.03, respectively). NMO spectrum eyes without ON history had lower macular RNFL thickness (p = 0.003), GCIP thickness (p = 0.002), outer nuclear layer thickness (p = 0.02), and low-contrast letter-acuity scores (2.5%: p = 0.03; 1.25%: p = 0.002) compared to healthy controls.

CONCLUSIONS

We have identified a pattern of retinal morphologic abnormalities in NMO that is associated with severe retinal axonal and neuronal loss and corresponding visual disability. MME may contribute to poor visual outcomes following NMO-associated ON or alternatively represent a marker of ON severity. Additionally, our results support that subclinical involvement of the anterior visual pathway may occur in NMO spectrum disorders.

Distinction of seropositive NMO spectrum disorder and MS brain lesion distribution

OBJECTIVE

Neuromyelitis optica and its spectrum disorder (NMOSD) can present similarly to relapsing-remitting multiple sclerosis (RRMS). Using a quantitative lesion mapping approach, this research aimed to identify differences in MRI brain lesion distribution between aquaporin-4 antibody-positive NMOSD and RRMS, and to test their diagnostic potential.

METHODS

Clinical brain MRI sequences for 44 patients with aquaporin-4 antibody-positive NMOSD and 50 patients with RRMS were examined for the distribution and morphology of brain lesions. T2 lesion maps were created for each subject allowing the quantitative comparison of the 2 conditions with lesion probability and voxel-wise analysis.

RESULTS

Sixty-three percent of patients with NMOSD had brain lesions and of these 27% were diagnostic of multiple sclerosis. Patients with RRMS were significantly more likely to have lesions adjacent to the body of the lateral ventricle than patients with NMOSD. Direct comparison of the probability distributions and the morphologic attributes of the lesions in each group identified criteria of "at least 1 lesion adjacent to the body of the lateral ventricle and in the inferior temporal lobe; or the presence of a subcortical U-fiber lesion; or a Dawson's finger-type lesion," which could distinguish patients with multiple sclerosis from those with NMOSD with 92% sensitivity, 96% specificity, 98% positive predictive value, and 86% negative predictive value.

CONCLUSION

Careful inspection of the distribution and morphology of MRI brain lesions can distinguish RRMS and NMOSD.

Clinical relevance of serum aquaporin-4 antibody levels in neuromyelitis optica

Neuromyelitis optica (NMO) is an inflammatory disease that selectively affects the optic nerves and spinal cord. The discovery of NMO-IgG targeting aquaporin-4 (AQP4) in NMO patients suggested that NMO is a distinct entity, with a fundamentally different etiology from that of multiple sclerosis (MS). Although NMO usually leads to grave disability because of the more severe tissue destruction compared with classical MS, there have been several reports describing a benign form of NMO over a long disease term. NMO-IgG/AQP4 antibodies show high specificity but medium sensitivity for NMO, while the clinical relevance of AQP4 antibody titers remains to be determined. We aimed to clarify the clinical relevance of AQP4 antibody levels determined by a bridging enzyme-linked immunosorbent assay in 38 patients with NMO or NMO spectrum disorder. The AQP4 antibody levels were higher in patients with optic neuritis (ON) than in those without ON (p = 0.0164). Among the 12 patients examined in a longitudinal study, four showed an increase in the ELISA values during some relapses, and eight showed no clear correlation between the ELISA values and relapse. Of the four patients who demonstrated a steady rise in the antibody levels over time, two patients had no concomitant relapses, despite elevation of the AQP4 antibody levels. We conclude that high AQP4 antibody levels are associated with the occurrence of ON, but that the antibody levels themselves are not closely correlated with the onset of relapse.

Ultrahigh-Field MR (7 T) Imaging of Brain Lesions in Neuromyelitis Optica

Background. Brain lesions are common in neuromyelitis optica spectrum disorder (NMOsd) and may resemble lesions of multiple sclerosis (MS). Objectives. To describe the imaging characteristics of supratentorial lesions in NMOsd on ultrahigh-field (7 T) MRI with special attention to vessel-lesion relationship. Methods. Ten NMOsd patients, all women and all seropositive for NMO IgG, with mean age of 51.3 ± 15.4 years and disease duration of 9.2 ± 6.4 years, were scanned at a 7 T whole-body human MR system with high-resolution 2D gradient echo sequence optimized to best visualize lesions and venous structures, T2- and T1-weighted imaging. Results. In 10 patients with NMOsd, a total of 92 lesions were observed (mean: 9.2 ± 8.8; range: 2-30), but only 8 lesions (9%) were traversed by a central venule. All lesions were <5 mm in diameter, and 83% were located in subcortical white matter. There were no lesions in the cortex or basal ganglia. Two patients exhibited diffuse periependymal abnormalities on FLAIR. Conclusions. Small, subcortical lesions without a central venule are the most consistent finding of NMOsd on 7 T MRI of the brain. Ultrahigh-field imaging may be useful for differentiating between NMOsd and MS.

The diagnostic and prognostic value of neurofilament heavy chain levels in immune-mediated optic neuropathies

Background. Loss of visual function differs between immune-mediated optic neuropathies and is related to axonal loss in the optic nerve. This study investigated the diagnostic and prognostic value of a biomarker for neurodegeneration, the neurofilament heavy chain (NfH) in three immune-mediated optic neuropathies. Methods. A prospective, longitudinal study including patients with optic neuritis due to multiple sclerosis (MSON, n = 20), chronic relapsing inflammatory optic neuritis (CRION, n = 19), neuromyelitis optica (NMO, n = 9), and healthy controls (n = 28). Serum NfH-SMI35 levels were quantified by ELISA. Findings. Serum NfH-SMI35 levels were highest in patients with NMO (mean 0.79 ± 1.51 ng/mL) compared to patients with CRION (0.13 ± 0.16 ng/mL, P = 0.007), MSON (0.09 ± 0.09, P = 0.008), and healthy controls (0.01 ± 0.02 ng/mL, P = 0.001). High serum NfH-SMI35 levels were related to poor visual outcome. Conclusions. Blood NfH-SMI35 levels are of moderate diagnostic and more important prognostic value in immune-mediated optic neuropathies. We speculate that longitudinal blood NfH levels may help to identify particular disabling events in relapsing conditions.

Immunological follow-up of patients with neuromyelitis optica: Is there a good biomarker?

A serial assessment of biomarkers related to disease activity could be clinically useful in some autoimmune diseases. Neuromyelitis optica (NMO) is a severe inflammatory disease of the optic nerves and spinal cord that can be associated with lupus erythematosus, Sjögren syndrome or myasthenia gravis. In this review, we discuss the existing data on the use of biomarkers of disease activity in NMO. A specific and pathogenic antibody (Ab) directed against aquaporin 4 (AQP4) was recently discovered in this disease. The relapses were frequently accompanied by a rise and immunosuppressive therapy by a decrease in serum anti-AQP4 Ab concentrations. However, this association is not strong enough to justify treatment changes based only on anti-AQP4 Ab level variations. This parameter might be helpful as a longitudinal biomarker but only if a threshold inducing a relapse and justifying a switch in therapy can be established. A link between disease severity and serum cytotoxicity against AQP4-expressing cells was proposed but has not yet been confirmed. Finally, the assessment of T cell immunity against AQP4 and specific cytokines could be future directions for research.

Clinical neuropathology practice guide 5-2012: updated guideline for the diagnosis of antineuronal antibodies

In recent years there is an increasing description of novel anti-neuronal antibodies that are associated with paraneoplastic and non-paraneoplastic neurological syndromes. These antibodies are useful in clinical practice to confirm the immunmediated origin of the neurological disorder and are helpful in tumor search. Currently, anti-neuronal antibodies can be classified according to the location of the recognized antigen into two groups, 1.) intraneuronal antigens and 2.) antigens located in the cell membrane. Different techniques are established for detecting these antibodies: tissue-based assay (TBA), cell-based assay (CBA), immunoblot, immunoprecipitation assay (IP), and ELISA. TBA detect most of the antibodies, however, different pretreatment methods of rat brain are necessary to visualize either Group 1 or 2 antibodies. Higher specificity is provided by immunoblots, applicable for Group 1 antibodies, and CBA, suitable for Group 2 antibodies. IP and ELISA may be useful for the detection of specific antibodies or to solve particular issues such as antibody titers. Diagnosis of paraneoplastic and non-paraneoplastic neurological syndromes has important implications on treatment and follow-up of patients. Selection and proper combination of test systems and appropriate knowledge of the clinical information will provide a maximum of sensitivity and specificity in identifying the associated antibody.

Neuromyelitis optica

Neuromyelitis optica (NMO) is a disabling inflammatory condition that targets astrocytes in the optic nerves and spinal cord. Neuro-ophthalmologists must be particularly aware of this disorder because about half of patients present as isolated unilateral optic neuritis months or years before a disease-defining and often crippling bout of myelitis. NMO is easily confused with multiple sclerosis because it is characterized by relapses that lead to stepwise accrual of deficits. The best predictor of conversion from optic neuritis to clinical definite NMO is the presence of a serum antibody to aquaporin-4 called NMO-IgG. However, this test is currently only about 75% sensitive. Suspicion of NMO should be high in patients who present with vision of light perception or worse or who are left with acuity of 20/50 or worse after optic neuritis and in those with simultaneous bilateral optic neuritis or recurrent attacks. Acute NMO relapses are generally treated with high-dose intravenous steroids, with plasma exchange often used as a rescue therapy for those who do not respond. Preventative strategies against relapses currently use broad-spectrum or selective B-lymphocyte immune suppression, but their use is based on small, generally uncontrolled studies. Hopefully, the future will bring more sensitive tools for defining risk and predicting outcome, as well as more targeted and effective forms of therapy.

The spectrum of neuromyelitis optica (NMO) in childhood

The evaluation of inflammatory central nervous system disorders in childhood with predominant involvement of the optic nerves and spinal cord has been greatly enhanced over the last decade with identification of a group of disorders unified by the detection of neuromyelitis optica (NMO)-IgG, an antibody targeting the central nervous system-predominant water channel aquaporin-4. Clinical syndromes are predominated by the relapsing form of NMO but also include encephalopathic variants that can mimic acute disseminated encephalomyelitis. Maintenance immunotherapy is used to prevent relapses in NMO-IgG-seropositive patients. In contrast, NMO-IgG-seronegative children with NMO more commonly have a monophasic course (simultaneous occurrence of optic neuritis and transverse myelitis) and do not require remission-maintaining immunotherapy, but close surveillance is advised. Current clinical, pathological, and pathogenetic knowledge is reviewed with a focus on clinical presentation, neuroimaging findings, serological investigations, and treatment of children with disorders within the spectrum of central nervous system aquaporin-4 autoimmunity.

Meningoencephalitis as an initial manifestation of neuromyelitis optica spectrum disorder

Two patients presented with initial symptoms of headache and fever, and two weeks later had disturbance of consciousness. Cerebrospinal fluid (CSF) showed pleocytosis >500×10²/L. Magnetic resonance imaging (MRI) showed multiple brain lesions at sites of high aquaporin-4 (AQP-4) expression. Case 1 presented optic neuritis four years after the first attack and case 2 had symptoms of myelitis three weeks after headache. Serum AQP-4 antibody was positive in both cases, and the diagnosis of neuromyelitis optica spectrum disorder (NMOSD) was made. Accordingly, NMOSD can initially present as meningoencephalitis mimicking intracranial infection, and the characteristic MRI imaging is quite critical for differentiation.

Antibodies to surface dopamine-2 receptor in autoimmune movement and psychiatric disorders

Recent reports of autoantibodies that bind to neuronal surface receptors or synaptic proteins have defined treatable forms of autoimmune encephalitis. Despite these developments, many cases of encephalitis remain unexplained. We have previously described a basal ganglia encephalitis with dominant movement and psychiatric disease, and proposed an autoimmune aetiology. Given the role of dopamine and dopamine receptors in the control of movement and behaviour, we hypothesized that patients with basal ganglia encephalitis and other putative autoimmune basal ganglia disorders harboured serum autoantibodies against important dopamine surface proteins. Basal ganglia encephalitis sera immunolabelled live surface cultured neurons that have high expression of dopamine surface proteins. To detect autoantibodies, we performed flow cytometry cell-based assays using human embryonic kidney cells to express surface antigens. Twelve of 17 children (aged 0.4-15 years, nine males) with basal ganglia encephalitis had elevated immunoglobulin G to extracellular dopamine-2 receptor, compared with 0/67 controls. Immunofluorescence on wild-type mouse brain showed that basal ganglia encephalitis sera immunolabelled microtubule-associated protein 2-positive neurons in striatum and also in cultured striatal neurons, whereas the immunolabelling was significantly decreased in dopamine-2 receptor knock-out brains. Immunocytochemistry confirmed that immunoreactivity localized to the surface of dopamine-2 receptor-transfected cells. Immunoabsorption of basal ganglia encephalitis sera on dopamine-2 receptor-transfected human embryonic kidney cells decreased immunolabelling of dopamine-2 receptor-transfected human embryonic kidney cells, neurons and wild-type mouse brain. Using a similar flow cytometry cell-based assay, we found no elevated immunoglobulin G binding to dopamine 1, 3 or 5 receptor, dopamine transporter or N-methyl-d-aspartate receptor. The 12 dopamine-2 receptor antibody-positive patients with encephalitis had movement disorders characterized by parkinsonism, dystonia and chorea. In addition, the patients had psychiatric disturbance with emotional lability, attention deficit and psychosis. Brain magnetic resonance imaging showed lesions localized to the basal ganglia in 50% of the patients. Elevated dopamine-2 receptor immunoglobulin G was also found in 10/30 patients with Sydenham's chorea, 0/22 patients with paediatric autoimmune neuropsychiatric disorders associated with streptococcal infection and 4/44 patients with Tourette's syndrome. No dopamine-1 receptor immunoglobulin G was detected in any disease or control groups. We conclude that assessment of dopamine-2 receptor antibodies can help define autoimmune movement and psychiatric disorders.

The expanded spectrum of neuromyelitis optica: evidences for a new definition

Neuromyelitis optica (NMO) has been traditionally described as the association of recurrent or bilateral optic neuritis and longitudinally extensive transverse myelitis (LETM). Identification of aquaporin-4 antibody (AQP4-IgG) has deeply changed the concept of NMO. A spectrum of NMO disorders (NMOSD) has been formulated comprising conditions which include both AQP4-IgG seropositivity and one of the index events of the disease (recurrent or bilateral optic neuritis and LETM). Most NMO patients harbor asymptomatic brain MRI lesions, some of them considered as typical of NMO. Some patients with aquaporin-4 autoimmunity present brainstem, hypothalamic or encephalopathy symptoms either preceding an index event or occurring isolatedly with no evidence of optic nerve or spinal involvement. On the opposite way, other patients have optic neuritis or LETM in association with typical lesions of NMO on brain MRI and yet are AQP4-IgG seronegative. An expanded spectrum of NMO disorders is proposed to include these cases.

Astrocytic autoantibody of neuromyelitis optica (NMO-IgG) binds to aquaporin-4 extracellular loops, monomers, tetramers and high order arrays

The principal central nervous system (CNS) water channel, aquaporin-4 (AQP4), is confined to astrocytic and ependymal membranes and is the target of a pathogenic autoantibody, neuromyelitis optica (NMO)-IgG. This disease-specific autoantibody unifies a spectrum of relapsing CNS autoimmune inflammatory disorders of which NMO exemplifies the classic phenotype. Multiple sclerosis and other immune-mediated demyelinating disorders of the CNS lack a distinctive biomarker. Two AQP4 isoforms, M1 and M23, exist as homotetrameric and heterotetrameric intramembranous particles (IMPs). Orthogonal arrays of predominantly M23 particles (OAPs) are an ultrastructural characteristic of astrocytic membranes. We used high-titered serum from 32 AQP4-IgG-seropositive patients and 85 controls to investigate the nature and molecular location of AQP4 epitopes that bind NMO-IgG, and the influence of supramolecular structure. NMO-IgG bound to denatured AQP4 monomers (68% of cases), to native tetramers and high order arrays (90% of cases), and to AQP4 in live cell membranes (100% of cases). Disease-specific epitopes reside in extracellular loop C more than in loops A or E. IgG binding to intracellular epitopes lacks disease specificity. These observations predict greater disease sensitivity and specificity for tissue-based and cell-based serological assays employing "native" AQP4 than assays employing denatured AQP4 and fragments. NMO-IgG binds most avidly to plasma membrane surface AQP4 epitopes formed by loop interactions within tetramers and by intermolecular interactions within high order structures. The relative abundance and localization of AQP4 high order arrays in distinct CNS regions may explain the variability in clinical phenotype of NMO spectrum disorders.

Diagnostic utility of NMO/AQP4-IgG in evaluating CNS inflammatory disease in Thai patients

Epidemiological studies in Thailand have reported that inflammatory demyelinating diseases (IDDs) commonly affect the optic nerve and spinal cord. We investigated the diagnostic utility of aquaporin (AQP)-4-IgG testing in 31 consecutive patients evaluated for CNS IDDs in 3 academic Thai hospital neurology clinics between February 2008 and January 2009. Patients were classified into 3 clinical diagnostic groups: Neuromyelitis optica (NMO, n=10) multiple sclerosis (MS, n=5) and unclassified IDD (n=16). All sera were tested blindly by cell binding (Euroimmun) assay (CBA). Sera were also tested by indirect immunofluorescence assay (IFA) and ELISA (RSR/Kronus). After initial screening by CBA, AQP4-IgG was detected in 6 NMO patients (60%); 3 of the 4 seronegative cases were receiving immunosuppressants. AQP4-IgG was detected in 13 unclassified IDD cases (81%), but in no MS cases. Cell binding assay and ELISA were more sensitive than IFA (p=0.0004). The 81% seropositivity rate in "unclassified" patients suggests that AQP4 autoimmunity accounts for a significant proportion of Thai CNS inflammatory demyelinating disease, especially those with optic neuritis or transverse myelitis, with or without abnormal brain MRI, in whom a specific diagnosis or clear-cut treatment approach is unclear.

Evaluation of a multiparametric immunofluorescence assay for standardization of neuromyelitis optica serology

BACKGROUND

Neuromyelitis optica (NMO) is a severely disabling autoimmune disorder of the central nervous system, which predominantly affects the optic nerves and spinal cord. In a majority of cases, NMO is associated with antibodies to aquaporin-4 (AQP4) (termed NMO-IgG).

AIMS

In this study, we evaluated a new multiparametric indirect immunofluorescence (IIF) assay for NMO serology.

METHODS

Sera from 20 patients with NMO, 41 patients with multiple sclerosis (MS), 30 healthy subjects, and a commercial anti-AQP4 IgG antibody were tested in a commercial composite immunofluorescence assay ("Neurology Mosaic 17"; Euroimmun, Germany), consisting of five different diagnostic substrates (HEK cells transfected with AQP4, non-transfected HEK cells, primate cerebellum, cerebrum, and optic nerve tissue sections).

RESULTS

We identified AQP4 specific and non-specific fluorescence staining patterns and established positivity criteria. Based on these criteria, this kit yielded a high sensitivity (95%) and specificity (100%) for NMO and had a significant positive and negative likelihood ratio (LR+ = ∞, LR- = 0.05). Moreover, a 100% inter- and intra-laboratory reproducibility was found.

CONCLUSIONS

The biochip mosaic assay tested in this study is a powerful tool for NMO serology, fast to perform, highly sensitive and specific for NMO, reproducible, and suitable for inter-laboratory standardization as required for multi-centre clinical trials.

Aquaporin 4 and neuromyelitis optica

Neuromyelitis optica is an inflammatory demyelinating disorder of the CNS. The discovery of circulating IgG1 antibodies against the astrocyte water channel protein aquaporin 4 (AQP4) and the evidence that AQP4-IgG is involved in the development of neuromyelitis optica revolutionised our understanding of the disease. However, important unanswered questions remain--for example, we do not know the cause of AQP4-IgG-negative disease, how astrocyte damage causes demyelination, the role of T cells, why peripheral AQP4-expressing organs are undamaged, and how circulating AQP4-IgG enters neuromyelitis optica lesions. New drug candidates have emerged, such as aquaporumab (non-pathogenic antibody blocker of AQP4-IgG binding), sivelestat (neutrophil elastase inhibitor), and eculizumab (complement inhibitor). Despite rapid progress, randomised clinical trials to test new drugs will be challenging because of the small number of individuals with the disorder.

Myasthenia gravis and neuromyelitis optica spectrum disorder: a multicenter study of 16 patients

OBJECTIVE

To describe 16 patients with a coincidence of 2 rare diseases: aquaporin-4 antibody (AQP4-Ab)-mediated neuromyelitis optica spectrum disorder (AQP4-NMOSD) and acetylcholine receptor antibody (AChR-Ab)-mediated myasthenia gravis (AChR-MG).

METHODS

The clinical details and antibody results of 16 patients with AChR-MG and AQP4-NMOSD were analyzed retrospectively.

RESULTS

All had early-onset AChR-MG, the majority with mild generalized disease, and a high proportion achieved remission. Fifteen were female; 11 were Caucasian. In 14/16, the MG preceded NMOSD (median interval: 16 years) and 11 of these had had a thymectomy although 1 only after NMOSD onset. In 4/5 patients tested, AQP4-Abs were detectable between 4 and 16 years prior to disease onset, including 2 patients with detectable AQP4-Abs prior to thymectomy. AChR-Abs decreased and the AQP4-Ab levels increased over time in concordance with the relevant disease. AChR-Abs were detectable at NMOSD onset in the one sample available from 1 of the 2 patients with NMOSD before MG.

CONCLUSIONS

Although both conditions are rare, the association of MG and NMOSD occurs much more frequently than by chance and the MG appears to follow a benign course. AChR-Abs or AQP4-Abs may be present years before onset of the relevant disease and the antibody titers against AQP4 and AChR tend to change in opposite directions. Although most cases had MG prior to NMOSD onset, and had undergone thymectomy, NMOSD can occur first and in patients who have not had their thymus removed.