NMO-IgG in the diagnosis of neuromyelitis optica

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.

Neuromyelitis optica: an often forgotten cause of intractable nausea and vomiting

Neuromyelitis optica, also known as Devic's disease, is a rare autoimmune disorder in which a patient's immune system affects the optic nerves and the spinal cord, leading to loss of vision and spinal cord dysfunction. We present our experience with a 38-year-old female who presented to our facility with complaints of intractable nausea and vomiting. After extensive evaluation, she was found to have neuromyelitis optica. Her symptoms completely resolved following institution of appropriate therapy. She made a significant recovery and has since been placed on chronic immunosuppressive therapy. Through this article we hope to bring attention to a significant cause of intractable nausea and vomiting that may often be forgotten in general medicine or gastroenterology services.

Diagnostic biomarkers in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the CNS and comprises a heterogeneous spectrum of disease subtypes. The distinctive variability of clinical presentations, histopathologic and immunologic patterns, as well as neuroradiologic phenotypes in MS poses a diagnostic challenge to the attending physician and claims a more differentiated typing of MS patients by diagnostic biomarkers in order to anticipate the expected disease course and to stratify patients for specifically tailored therapies. In this paper, the major biomarkers presently recommended in the diagnosis of MS are reviewed, including magnetic resonance imaging, the analysis of cerebrospinal fluid parameters and the diagnostic relevance of antibodies to aquaporin-4 water channels and myelin antigens.

The history of neuromyelitis optica

The discovery of a novel serum autoantibody (termed NMO-IgG or AQP4-Ab) in a subset of patients in 2004 has revived interest in neuromyelitis optica (NMO). While the history of classical multiple sclerosis has been extensively studied, only little is known about the history of NMO. In the present article, we provide a comprehensive review of the early history of this rare but intriguing syndrome. We trace the origins of the concept of NMO in the 19th century medical literature and follow its evolution throughout the 20th and into the 21st century. Finally, we discuss recent proposals to revise the concept of NMO and explain why there is indeed a need for a more systematic and descriptive nomenclature.

Anti-AQP(4) antibody in idiopathic acute transverse myelitis with recurrent clinical course: frequency of positivity and influence in prognosis

BACKGROUND

The anti-aquaporin4 (anti-AQP4) antibody is specific for neuromyelitis optica (NMO), but is also found in limited forms. The presence of this antibody in acute transverse myelitis (ATM) has been associated with recurrence and conversion to NMO, but the influence on disability has not yet been described.

OBJECTIVE

To describe the frequency of anti-AQP4 in ATM and analyze the influence in long-term prognosis.

DESIGN

Cross-sectional and retrospective study.

METHODS

Consecutive ATM cases in a multiple sclerosis center in Rio de Janeiro, Brazil, from 2000 through 2009 were reviewed. Recurrent cases tested for anti-AQP4 were selected. ATM with magnetic resonance imaging spinal cord lesions extending over three or more vertebral segments was classified as longitudinally extensive transverse myelitis (LETM); Kurtzke scale was applied at last evaluation.

OUTCOME MEASURES

Frequency of anti-AQP4; severity of spinal cord dysfunction at last follow-up.

RESULTS

Twenty six patients (21 female:5 male; 17 white:9 African descent) were studied. The first ATM occurred at 38.04 ± 12.7 years. The interval between the first and the second ATM was eight months (1-150) and the number of ATM varied from two to seven. After 40.5 months (12-192) of disease, the median Expanded Disability Status Scale (EDSS) score was three (0-9). Anti-AQP4 antibody was positive in 26.9%. LETM was found in 65.4%. LETM presented later onset, higher disability and higher positivity to anti-AQP4 (LETM 41.2% versus no-LETM 0%, P = 0.024). Dysfunction at long-term follow-up was similar in anti-AQP4 positive and negative cases.

CONCLUSION

The frequency of anti-AQP4 in recurrent ATM was 26.9%, increasing to 41.2% among LETM. Presence of the antibody had no influence on morbidity.

Testing for antibodies to human aquaporin-4 by ELISA: sensitivity, specificity, and direct comparison with immunohistochemistry

BACKGROUND

Several assays have been developed to detect antibodies to aquaporin-4 (NMO-IgG/AQP4-Ab). However, many of these assays require sophisticated techniques and are thus only available at specialized laboratories. This is problematic since NMO-IgG/AQP4-Ab testing has important prognostic and therapeutic implications.

OBJECTIVE

To evaluate a newly developed, commercial, enzyme-linked immunosorbent assay (ELISA) for detecting NMO-IgG/AQP4-Ab.

METHODS

Serum samples from 261 patients with NMO spectrum disorders (NMOSD; n=108) and controls (n=153) were tested for AQP4-Ab by using ELISA. Of these patients, 207 were tested in parallel using a standard immunohistochemical (IHC) assay.

RESULTS

Fifty of 66 (75.8%) patients with NMO, 17/25 (68%) with LETM, 3/14 (21.4%) with ON, 2/3 (66.7%) with ON and non-extensive transverse myelitis, and 2/153 (1.3%) controls tested positive in the ELISA. Of those NMOSD patients tested by both ELISA and IHC, 10 were positive only in the ELISA and 3 exclusively in the IHC assay, suggesting that the overall sensitivity of the ELISA was higher than that of the standard IHC assay. The ELISA yielded very good intra- and inter-run reproducibility with regard to AQP4-Ab detection and good intrarun, but only moderate inter-run reproducibility with regard to AQP4-Ab quantification. Anti-AQP4 serum concentrations correlated with disease activity (p<0.00001), but did not differ between patients with NMO and patients with isolated LETM or ON.

CONCLUSION

The ELISA evaluated here provides a relatively sensitive and easy-to-use diagnostic tool for detecting antibodies to AQP4 and could make AQP4-Ab testing, which is of high clinical relevance, more widely available.

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.

Viruses and multiple sclerosis

Multiple sclerosis (MS) is a chronic demyelinating disorder of unknown etiology, possibly caused by a virus or virus-triggered immunopathology. The virus might reactivate after years of latency and lyse oligodendrocytes, as in progressive multifocal leukoencephalopathy, or initiate immunopathological demyelination, as in animals infected with Theiler's murine encephalomyelitis virus or coronaviruses. The argument for a viral cause of MS is supported by epidemiological analyses and studies of MS in identical twins, indicating that disease is acquired. However, the most important evidence is the presence of bands of oligoclonal IgG (OCBs) in MS brain and CSF that persist throughout the lifetime of the patient. OCBs are found almost exclusively in infectious CNS disorders, and antigenic targets of OCBs represent the agent that causes disease. Here, the authors review past attempts to identify an infectious agent in MS brain cells and discuss the promise of using recombinant antibodies generated from clonally expanded plasma cells in brain and CSF to identify disease-relevant antigens. They show how this strategy has been used successfully to analyze antigen specificity in subacute sclerosing panencephalitis, a chronic encephalitis caused by measles virus, and in neuromyelitis optica, a chronic autoimmune demyelinating disease produced by antibodies directed against the aquaporin-4 water channel.

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

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.

Contrasting disease patterns in seropositive and seronegative neuromyelitis optica: A multicentre study of 175 patients

Background

The diagnostic and pathophysiological relevance of antibodies to aquaporin-4 (AQP4-Ab) in patients with neuromyelitis optica spectrum disorders (NMOSD) has been intensively studied. However, little is known so far about the clinical impact of AQP4-Ab seropositivity.

Objective

To analyse systematically the clinical and paraclinical features associated with NMO spectrum disorders in Caucasians in a stratified fashion according to the patients' AQP4-Ab serostatus.

Methods

Retrospective study of 175 Caucasian patients (AQP4-Ab positive in 78.3%).

Results

Seropositive patients were found to be predominantly female (p < 0.0003), to more often have signs of co-existing autoimmunity (p < 0.00001), and to experience more severe clinical attacks. A visual acuity of ≤ 0.1 during acute optic neuritis (ON) attacks was more frequent among seropositives (p < 0.002). Similarly, motor symptoms were more common in seropositive patients, the median Medical Research Council scale (MRC) grade worse, and MRC grades ≤ 2 more frequent, in particular if patients met the 2006 revised criteria (p < 0.005, p < 0.006 and p < 0.01, respectively), the total spinal cord lesion load was higher (p < 0.006), and lesions ≥ 6 vertebral segments as well as entire spinal cord involvement more frequent (p < 0.003 and p < 0.043). By contrast, bilateral ON at onset was more common in seronegatives (p < 0.007), as was simultaneous ON and myelitis (p < 0.001); accordingly, the time to diagnosis of NMO was shorter in the seronegative group (p < 0.029). The course of disease was more often monophasic in seronegatives (p < 0.008). Seropositives and seronegatives did not differ significantly with regard to age at onset, time to relapse, annualized relapse rates, outcome from relapse (complete, partial, no recovery), annualized EDSS increase, mortality rate, supratentorial brain lesions, brainstem lesions, history of carcinoma, frequency of preceding infections, oligoclonal bands, or CSF pleocytosis. Both the time to relapse and the time to diagnosis was longer if the disease started with ON (p < 0.002 and p < 0.013). Motor symptoms or tetraparesis at first myelitis and > 1 myelitis attacks in the first year were identified as possible predictors of a worse outcome.

Conclusion

This study provides an overview of the clinical and paraclinical features of NMOSD in Caucasians and demonstrates a number of distinct disease characteristics in seropositive and seronegative patients.

Two cases of benign neuromyelitis optica in patients with celiac disease

Neuromyelitis optica (NMO) is an autoimmune inflammatory disorder of the central nervous system, which predominately affects optic nerves and spinal cord. Celiac disease (CD) or gluten sensitivity is an autoimmune enteropathy triggered by ingestion of wheat gliadin and related proteins in genetically susceptible individuals. Although NMO is associated with other autoimmune disorders in around 30% of cases, an association of NMO with CD has rarely been reported. We describe two Caucasian women who, nineteen and two years after diagnosis of CD, respectively, had recurrent episodes of myelitis and optic neuritis consistent with the diagnosis of NMO. Despite numerous relapses, NMO followed an unusually mild course with no persistent neurological deficit, indicating that recurrent NMO can follow a benign course with complete remission. We discuss in detail a possible link between NMO and pre-existing CD.

The case of the Marquis de Causan (1804): an early account of visual loss associated with spinal cord inflammation

The recent discovery of disease specific and pathogenic autoantibodies in neuromyelitis optica (NMO, Devic's disease) has revived the interest in this intriguing yet often devastating condition. While the history of classic multiple sclerosis has been studied extensively, only very little is known so far about the early history of NMO. Here we discuss a now forgotten report by the famous French anatomist and pathologist Antoine Portal (1742-1832), first physician to Louis XVIII and founding and lifelong president of the Académie Nationale de Médecine. Portal's report, which fascinated some of the most renowned 19th century pioneers in the field of neurology but fell into oblivion later, represents the first account of visual loss in a patient with spinal cord inflammation but no brain pathology in the Western literature known so far--published more than 60 years prior to Thomas Clifford Allbutt's much cited note on a patient with myelitis and a "sympathetic eye disorder".

Neuromyelitis optica immunoglobulin G in Chinese patients detected by immunofluorescence assay on a monkey brain substrate

BACKGROUND

Serum neuromyelitis optica immunoglobulin G (NMO-IgG) is used as a biomarker to differentiate between neuromyelitis optica (NMO) and multiple sclerosis (MS). However, the original assay is expensive and complex and shows low sensitivity. Here, we investigated the potential of NMO-IgG detection using an indirect immunofluorescence (IIF) assay on monkey brains.

METHODS

NMO-IgG seroprevalence was determined in 168 samples by an IIF assay on a monkey brain substrate. The data were compared with those from a standard mouse brain IIF assay using McNemar and kappa tests.

RESULTS

Thirty-one of 50 (62%) NMO patients, 7 of 18 (38.9%) longitudinally extensive transverse myelitis patients, 6 of 57 (10.5%) MS patients, and 5 of 10 (50%) optic neuritis patients were seropositive for NMO-IgG. None of the acute partial transverse myelitis patients (n = 3) or healthy controls (n = 20) was positive. Thus, the sensitivity of the test was 62% for the patients with clinically definite NMO. The specificity was 89.5%, considering the 57 MS patients as the control group. The modified IIF assay on monkey brains and the standard IIF assay based on mouse brains were not significantly different (McNemar test; p = 1.000). The two assays were concordant in 39 seropositive samples and 100 seronegative samples (kappa test; kappa = 0.592, p < 0.0001).

CONCLUSIONS

Although the modified IIF monkey brain assay was no better than the standard mouse brain IIF assay, we affirmed that NMO-IgG is a sensitive and specific biomarker to differentiate between NMO and MS.

Neuromyelitis optica spectrum disorders in patients with myasthenia gravis: ten new aquaporin-4 antibody positive cases and a review of the literature

BACKGROUND

Neuromyelitis optica (NMO, Devic syndrome) and myasthenia gravis (MG) are rare antibody-mediated autoimmune disorders. Concurrent incidence has been reported in only few patients, mostly non-Caucasians.

OBJECTIVE

To report on ten Caucasian patients with NMO spectrum disorders (NMOSD) and MG and to provide a comprehensive review of the literature.

METHOD

Retrospective study.

RESULTS

In total, 26 patients (m:f = 1:12; Caucasian in 12) with MG (generalized in 17) and NMOSD (NMO in 21, longitudinally extensive transverse myelitis in five) were identified from the authors' own files (n = 10) and the previous literature (n = 16). MG preceded NMOSD in 24/25 cases (96%). AQP4-Ab were tested in 20 patients and were positive in 17 (85%). Twenty out of 25 patients (80%) had been treated with thymectomy or thymic irradiation, which preceded NMOSD in all cases (median latency, 12 years; range, 0.3-32). At last follow-up, complete remission of MG was reported in 15/22 (68%), and MG was well controlled with pyridostigmine in three. Co-existing autoimmune disorders or autoimmune antibodies were reported in 17 patients.

CONCLUSION

Our study demonstrates that i) AQP4-Ab-positive NMOSD are more commonly associated with MG in Caucasians than previously thought; ii) MG precedes NMOSD in most cases, often by more than a decade; iii) NMOSD almost exclusively occur in females with juvenile or early-onset MG; and iv) MG frequently takes an unusually mild course in patients with NMOSD. A history of thymectomy could be a possible risk factor for the later development of NMOSD. We recommend testing for AQP4-Ab in MG patients presenting with atypical motor or optic symptoms.

Antibodies to CV2/CRMP5 in neuromyelitis optica-like disease: case report and review of the literature

Neuromyelitis optica (NMO) is associated with antibodies to aquaporin-4 (termed NMO-IgG or AQP4-Ab) in 60-90% of cases. Little is known about the aetiology of NMO in NMO-IgG/AQP4-Ab negative patients. Here we report on CV2/CRMP5 antibodies in a 69-year-old male patient with NMO-IgG/AQP4-Ab negative NMO. The association of CV2/CRMP5-Ab with prostate cancer suggests a paraneoplastic aetiology of NMO in our patient. Our report strengthens the case of antibodies other than AQP4-Ab being involved in the immunopathogenesis in a subset of patients with NMO. We conclude that CV2/CRMP5-Ab should be included in the differential diagnosis of NMO, in particular if AQP4-Ab are negative and irrespective of whether a tumour is known or not. We recommend that recombinant tests, which are increasingly used because of their higher sensitivity and specificity, should always be accompanied by standard indirect immunofluorescence employing brain tissue sections in order to avoid CV2/CRMP5-Ab or other paraneoplastic antibodies being overlooked. In addition, we provide a comprehensive review of all patients with CV2/CRMP5-Ab and NMO-like disease published in the English literature so far.

'Noteomielite' accompanied by acute amaurosis (1844). An early case of neuromyelitis optica

So far, only very little is known about the early history of neuromyelitis optica (Devic's syndrome). Here, we discuss a then widely recognized but now forgotten 1844 report by the Genoese physician Giovanni Battista Pescetto (1806-1884) on a 42-year-old man, who simultaneously developed acute amaurosis and cervical myelitis. Pescetto's report represents the earliest account of a case of neuromyelitis optica in the Western literature known so far.

The differential diagnosis of longitudinally extensive transverse myelitis

Longitudinally extensive transverse myelitis refers to florid and widespread inflammation of the spinal cord causing T2 hyperintensity on spinal magnetic resonance imaging that is seen to extend over three or more vertebral segments. Whilst rare, longitudinally extensive transverse myelitis is clinically important as it can lead to catastrophic morbidity, and a group of these patients are at risk of further attacks. Early identification and establishment of the underlying aetiology is vital in order to initiate appropriate therapy and optimize outcomes. Whilst longitudinally extensive transverse myelitis is classically associated with neuromyelitis optica, there are many other causes. These include other inflammatory aetiologies, infection, malignancy and metabolic disturbance. Some of these are readily treatable. Laboratory and radiological investigations can help to differentiate these causes. Treatment of longitudinally extensive transverse myelitis hinges on distinguishing inflammatory and non-inflammatory aetiologies and identifying patients who are at high risk of a recurrent course.

Neuromyelitis optica (NMO)--an autoimmune disease of the central nervous system (CNS)

In the past 10 years, neuromyelitis optica (NMO) has evolved from Devic's categorical clinical description into a broader disease spectrum. Serum IgG antibodies have been identified in NMO patients with the water channel aquaporin-4 (AQP4) as their main target antigen. AQP4 antibodies/NMO-IgG have been shown to be a highly specific and moderately sensitive serum biomarker for NMO. The immunopathology of NMO lesions supports that anti-AQP4 antibodies/NMO-IgG are involved in the pathogenesis of NMO. In vitro studies have demonstrated that human NMO-IgG induce necrosis and impair glutamate transport in astrocytes. Certain ethnic groups, notably of Asian and African origin, seem to be more susceptible to NMO than others. The genetic background for these putative differences is not known, a weak human leucocyte antigen association has been identified. AQP4 gene variants could represent a genetic susceptibility factor for different clinical phenotypes within the NMO spectrum. Experimental models have been described including a double-transgenic myelin-specific B- and T-cell mouse. NMO-like disease has been induced with passive transfer of human anti-AQP4 antibodies to the plasma of mice with pre-established experimental autoimmune encephalomyelitis or by intrathecal administration to naive mice. NMO may be characterized as a channelopathy of the central nervous system with autoimmune characteristics.

Cerebrospinal fluid findings in aquaporin-4 antibody positive neuromyelitis optica: results from 211 lumbar punctures

BACKGROUND

Neuromyelitis optica (NMO, Devic disease) is a severely disabling autoimmune disorder of the CNS, which was considered a subtype of multiple sclerosis (MS) for many decades. Recently, however, highly specific serum autoantibodies (termed NMO-IgG or AQP4-Ab) have been discovered in a subset (60-80%) of patients with NMO. These antibodies were subsequently shown to be directly involved in the pathogenesis of the condition. AQP4-Ab positive NMO is now considered an immunopathogenetically distinct disease in its own right. However, to date little is known about the cerebrospinal fluid (CSF) in AQP4-Ab positive NMO.

OBJECTIVE

To describe systematically the CSF profile of AQP4-Ab positive patients with NMO or its formes frustes, longitudinally extensive myelitis and optic neuritis.

MATERIAL AND METHODS

Cytological and protein biochemical results from 211 lumbar punctures in 89 AQP4-Ab positive patients of mostly Caucasian origin with neuromyelitis optica spectrum disorders (NMOSD) were analysed retrospectively.

RESULTS

CSF-restricted oligoclonal IgG bands, a hallmark of MS, were absent in most patients. If present, intrathecal IgG (and, more rarely, IgM) synthesis was low, transient, and, importantly, restricted to acute relapses. CSF pleocytosis was present in around 50% of samples, was mainly mild (median, 19 cells/μl; range 6-380), and frequently included neutrophils, eosinophils, activated lymphocytes, and/or plasma cells. Albumin CSF/serum ratios, total protein and CSF L-lactate levels correlated significantly with disease activity as well as with the length of the spinal cord lesions in patients with acute myelitis. CSF findings differed significantly between patients with acute myelitis and patients with acute optic neuritis at the time of LP. Pleocytosis and blood CSF barrier dysfunction were also present during remission in some patients, possibly indicating sustained subclinical disease activity.

CONCLUSION

AQP4-Ab positive NMOSD is characterized by CSF features that are distinct from those in MS. Our findings are important for the differential diagnosis of MS and NMOSD and add to our understanding of the immunopathogenesis of this devastating condition.

Frequency and syndrome specificity of antibodies to aquaporin-4 in neurological patients with rheumatic disorders

Background: A new autoantibody (termed NMO-IgG, or AQP4-Ab) has recently been described in patients with neuromyelitis optica (NMO) and its formes frustes, longitudinally extensive transverse myelitis (LETM) and recurrent optic neuritis (rON). However, AQP4-Ab has been found also in patients with co-existing rheumatic diseases such as systemic lupus erythematosus (SLE) or Sjögren’s syndrome (SS), conditions which are characterized by broad, polyspecific B cell activation.

Objectives: In this study, we aimed at evaluating the syndrome specificity and frequency of AQP4-Ab in patients with rheumatic diseases and neurological symptoms.

Methods: For this purpose, serum samples from 109 neurological patients with established connective tissue disorders (CTD) ( n = 54), possible CTD ( n = 42), or vasculitis ( n = 13) were analysed for the presence of AQP4-Ab by a cell-based assay employing recombinant human AQP4.

Results: AQP4-Ab was detectable in 31/40 (78%) patients with CTD and NMO spectrum disorders (median titre, 1:1000) but in none of the samples obtained from patients with CTD or vasculitis and neurological disorders other than NMO, LETM, or rON ( n = 69).

Conclusion: The high syndrome specificity of the antibody for neuromyelitis optica spectrum disorders (NMOSDs) in patients with CTD supports the concept of AQP4-Ab being involved in the pathogenesis of these neurological conditions, and argues against AQP4-Ab simply being part of the polyclonal B cell activation generally associated with rheumatic diseases. Moreover, the finding that AQP4-Ab is present in patients with CTD and co-existing NMOSD with approximately the same frequency as in patients without CTD strengthens the case of CTD and AQP4-Ab positive NMOSD representing two co-existing yet distinct entities in the majority of patients.

Viruses and Multiple Sclerosis

Multiple sclerosis (MS) is a chronic demyelinating disorder of unknown etiology, possibly caused by a virus or virus-triggered immunopathology. The virus might reactivate after years of latency and lyse oligodendrocytes, as in progressive multifocal leukoencephalopathy, or initiate immunopathological demyelination, as in animals infected with Theiler’s murine encephalomyelitis virus or coronaviruses. The argument for a viral cause of MS is supported by epidemiological analyses and studies of MS in identical twins, indicating that disease is acquired. However, the most important evidence is the presence of bands of oligoclonal IgG (OCBs) in MS brain and CSF that persist throughout the lifetime of the patient. OCBs are found almost exclusively in infectious CNS disorders, and antigenic targets of OCBs represent the agent that causes disease. Here, the authors review past attempts to identify an infectious agent in MS brain cells and discuss the promise of using recombinant antibodies generated from clonally expanded plasma cells in brain and CSF to identify disease-relevant antigens. They show how this strategy has been used successfully to analyze antigen specificity in subacute sclerosing panencephalitis, a chronic encephalitis caused by measles virus, and in neuromyelitis optica, a chronic autoimmune demyelinating disease produced by antibodies directed against the aquaporin-4 water channel.

Bilateral and recurrent optic neuritis in multiple sclerosis

OBJECTIVE

To assess the frequency of bilateral and recurrent optic neuritis (ON) in multiple sclerosis (MS) and to compare these results with epidemiological data of ON in neuromyelitis optica (NMO) and recurrent ON without other signs of disease.

METHODS

We identified 472 patients with diagnosis of MS from the Swedish Multiple Sclerosis Register. These patients were evaluated for the presence of ON and whether the ON was the presenting symptom of MS; unilateral or bilateral; monophasic or recurrent.

RESULTS

Twenty-one percent presented with ON as their first manifestation of MS. The proportion of patients developing a second attack of ON before demonstration of other manifestations of MS was 5.5% and the frequency of recurrent bilateral ON as the presenting symptom was 3.8%. Only two patients presented with simultaneously appearing bilateral ON corresponding to 0.42%.

CONCLUSION

Recurrent ON, whether unilateral or bilateral, is a common presentation of MS. As MS is a much more common disease than NMO, care must be taken when evaluating the work-up of patients with recurrent ON. In some cases repeated MRI and lumbar punctures are warranted to improve diagnostic accuracy, even in the presence of the serological marker NMO-IgG.

Reappraisal of aquaporin-4 astrocytopathy in Asian neuromyelitis optica and multiple sclerosis patients

Selective aquaporin-4 (AQP4) loss and vasculocentric complement and immunoglobulin deposition are characteristic of neuromyelitis optica (NMO). We recently reported extensive AQP4 loss in demyelinated and myelinated layers of Baló's lesions without perivascular immunoglobulin and complement deposition. We aimed to reappraise AQP4 expression patterns in NMO and multiple sclerosis (MS). We evaluated AQP4 expression relative to glial fibrillary acidic protein, extent of demyelination, lesion staging (CD68 staining for macrophages), and perivascular deposition of complement and immunoglobulin in 11 cases with NMO and NMO spectrum disorders (NMOSD), five with MS and 30 with other neurological diseases. The lesions were classified as actively demyelinating (n = 66), chronic active (n = 86), chronic inactive (n = 48) and unclassified (n = 12). Six NMO/NMOSD and two MS cases showed preferential AQP4 loss beyond the demyelinated areas, irrespective of lesion staging. Five NMO and three MS cases showed AQP4 preservation even in actively demyelinating lesions, despite grave tissue destruction. Vasculocentric deposition of complement and immunoglobulin was detected only in NMO/NMOSD patients, with less than 30% of actively demyelinating lesions showing AQP4 loss. Our present and previous findings suggest that antibody-independent AQP4 loss can occur in heterogeneous demyelinating conditions, including NMO, Baló's disease and MS.

Temporal dynamics of cerebrospinal fluid anti-aquaporin-4 antibodies in patients with neuromyelitis optica spectrum disorders

Neuromyelitis optica spectrum disorders (NMOSD) are associated with anti-aquaporin-4 autoantibodies (AQP4-IgG). Limited data is available on longitudinal cerebrospinal fluid (CSF) AQP4-IgG and their relation to disease activity and inflammatory parameters. AQP4-IgG titers were measured in matched longitudinal serum and CSF samples of 12 patients with NMOSD by an immunofluorescence assay and correlated with clinical parameters. CSF AQP4-IgG were present in patients with high serum titers and correlated with spinal MRI lesion length and CSF parameters. Clinical improvement was associated with a decrease in CSF, but not serum, AQP4-IgG titers. Thus, CSF AQP4-IgG were associated with clinical activity and neuroinflammation.

AQP4 antibodies in neuromyelitis optica: diagnostic and pathogenetic relevance

Antibodies to aquaporin-4 (also known as AQP4-Ab or NMO-IgG) are sensitive and highly specific serum markers of autoimmune neuromyelitis optica (NMO). Second-generation recombinant diagnostic assays can detect AQP4-Ab in >or=80% of patients with NMO, and a role for AQP4-Ab in the pathophysiology of this condition was corroborated by a series of in vitro studies that demonstrated disruption of the blood-brain barrier, impairment of glutamate homeostasis and induction of necrotic cell death by AQP4-Ab-positive serum. Additional evidence for such a role has emerged from clinical observations, including the demonstration of a correlation between serum levels of AQP4-Ab and disease activity. The finding of NMO-like CNS lesions and clinical disease following passive transfer of AQP4-Ab-positive serum in several independent animal studies provided definitive proof for a pathogenic role of AQP4-Ab in vivo. Together, these findings provide a strong rationale for the use of therapies targeted against B cells or antibodies in the treatment of NMO. In this Review, we summarize the latest evidence in support of a direct involvement of AQP4-Ab in the immunopathogenesis of NMO, and critically appraise the diagnostic tests currently available for the detection of this serum reactivity.

Cerebrospinal fluid antibodies to aquaporin-4 in neuromyelitis optica and related disorders: frequency, origin, and diagnostic relevance

Background

In 70-80% of cases, neuromyelitis optica (NMO) is associated with highly specific serum auto-antibodies to aquaporin-4 (termed AQP4-Ab or NMO-IgG). Recent evidence strongly suggests that AQP4-Ab are directly involved in the immunopathogenesis of NMO.

Objective

To assess the frequency, syndrome specificity, diagnostic relevance, and origin of cerebrospinal fluid (CSF) AQP4-Ab in patients with NMO spectrum disorders (NMOSD).

Methods

87 CSF samples from 37 patients with NMOSD and 42 controls with other neurological diseases were tested for AQP4-Ab in a cell based assay using recombinant human AQP4. Twenty-three paired CSF and serum samples from AQP4-Ab seropositive NMOSD patients were further analysed for intrathecal IgG synthesis to AQP4.

Results

AQP4-Ab were detectable in 68% of CSF samples from AQP4-Ab seropositive patients with NMOSD, but in none of the CSF samples from AQP4-Ab seronegative patients with NMOSD and in none of the control samples. Acute disease relapse within 30 days prior to lumbar puncture, AQP4-Ab serum titres >1:250, and blood-CSF barrier dysfunction, but not treatment status, predicted CSF AQP4-Ab positivity. A positive AQP4-specific antibody index was present in 1/23 samples analysed.

Conclusions

AQP4-Ab are detectable in the CSF of most patients with NMOSD, mainly during relapse, and are highly specific for this condition. In the cohort analysed in this study, testing for CSF AQP4-Ab did not improve the sensitivity and specificity of the current diagnostic criteria for NMO. The substantial lack of intrathecal AQP4-Ab synthesis in patients with NMOSD may reflect the unique localisation of the target antigen at the blood brain barrier, and is important for our understanding of the immunopathogenesis of the disease.

Aquaporin-4 autoantibodies in neuromyelitis optica spectrum disorders: comparison between tissue-based and cell-based indirect immunofluorescence assays

BACKGROUND

Neuromyelitis optica spectrum disorders (NMOSD) are severe central nervous system inflammatory demyelinating disorders (CNS IDD) characterized by monophasic or relapsing, longitudinally extensive transverse myelitis (LETM) and/or optic neuritis (ON). A significant proportion of NMOSD patients are seropositive for aquaporin-4 (AQP4) autoantibodies. We compared the AQP4 autoantibody detection rates of tissue-based indirect immunofluorescence assay (IIFA) and cell-based IIFA.

METHODS

Serum of Chinese CNS IDD patients were assayed for AQP4 autoantibodies by tissue-based IIFA using monkey cerebellum and cell-based IIFA using transfected HEK293 cells which express human AQP4 on their cell membranes.

RESULTS

In total, 128 CNS IDD patients were studied. We found that 78% of NMO patients were seropositive for AQP4 autoantibodies by cell-based IIFA versus 61% by tissue-based IFA (p = 0.250), 75% of patients having relapsing myelitis (RM) with LETM were seropositive by cell-based IIFA versus 50% by tissue-based IIFA (p = 0.250), and 33% of relapsing ON patients were seropositive by cell-based IIFA versus 22% by tissue-based IIFA (p = 1.000); however the differences were not statistically significant. All patients seropositive by tissue-based IIFA were also seropositive for AQP4 autoantibodies by cell-based IIFA. Among 29 NMOSD patients seropositive for AQP4 autoantibodies by cell-based IIFA, 20 (69%) were seropositive by tissue-based IIFA. The 9 patients seropositive by cell-based IIFA while seronegative by tissue-based IIFA had NMO (3), RM with LETM (3), a single attack of LETM (1), relapsing ON (1) and a single ON attack (1). Among 23 NMO or RM patients seropositive for AQP4 autoantibodies by cell-based IIFA, comparison between those seropositive (n = 17) and seronegative (n = 6) by tissue-based IIFA revealed no differences in clinical and neuroradiological characteristics between the two groups.

CONCLUSION

Cell-based IIFA is slightly more sensitive than tissue-based IIFA in detection of AQP4 autoantibodies, which are highly specific for NMOSD.

Anti-aquaporin-4 antibodies in Devic's neuromyelitis optica: therapeutic implications

Devic's neuromyelitis optica (DNMO) is a demyelinating and inflammatory disease of the central nervous system (CNS) essentially restricted to the spinal cord and the optic nerves. It is a rare disorder with a prevalence estimated at less than 1/100,000 in Western countries. Since the first description by Eugène Devic in 1894, the relationship between DNMO and multiple sclerosis (MS) has been controversial. Recent clinical, epidemiological, pathological and immunological data demonstrate that MS and DNMO are distinct entities. This distinction between DNMO and MS is crucial, as prognosis and treatment are indeed different. DNMO is now considered to be an autoimmune, antibody-mediated disease especially since the identification of a specific serum autoantibody, named NMO-IgG and directed against the main water channel of the CNS, aquaporin-4 (AQP4). The assessment of AQP4 antibodies (Abs) has initially been proposed to differentiate DNMO and MS. It has also enlarged the clinical spectrum of DNMO and proved to be helpful in predicting relapses and conversion to DNMO after a first episode of longitudinally extensive transverse myelitis or isolated optic neuritis. Lastly, the discovery of the pathogenic role of AQP4 Abs in DNMO leads to a better understanding of detailed DNMO immunopathology and the elaboration of relevant novel treatment strategies specific to DNMO. In this review, we summarize the present and future therapeutic implications generated by the discovery of the various pathogenic mechanisms of AQP4 Abs in DNMO pathophysiology.

Aquaporin-4 water channel expression by thymoma of patients with and without myasthenia gravis

BACKGROUND

Neuromyelitis optica (NMO) is a serious idiopathic inflammatory demyelinating disorder characterized by acute transverse myelitis and optic neuritis. A significant proportion of NMO patients are seropositive for NMO-IgG, an autoantibody targeting aquaporin-4 (AQP4) water channel. Paraneoplastic NMO associated various tumors were recently reported.

AIM

We studied the expression of AQP4 by thymoma from patients with and without myasthenia gravis (MG).

METHODS

Thymoma obtained from thymomectomy in patients with and without MG were studied by immunohistochemistry and western blot.

RESULTS

Ten thymoma patients (9 with MG) and two control patients without thymoma or MG were studied. Immunohistochemistry revealed AQP4 immunoreactivity in cell membrane of thymoma cells from all ten thymoma specimens whereas thymic tissues from patients without thymoma or MG were negative for AQP4 immunoreactivity. Western blot revealed that lysates of nine of the ten thymoma specimens reacted with anti-human AQP4 antibody with a band of ~30 kDa compatible with the molecular weight of AQP4. Interestingly, immunofluorescence revealed that IgG isolated from 2 NMO patients seropositive for NMO-IgG bound to cell membrane of thymoma cells from all ten thymoma specimens while IgG from healthy control subject did not.

CONCLUSION

Thymoma cells of patients with and without MG express AQP4. AQP4 autoantibodies from serum of NMO patients bound to AQP4 expressed on thymoma cell membrane.

Immunoglobulin M antibodies to aquaporin-4 in neuromyelitis optica and related disorders

BACKGROUND

Neuromyelitis optica (NMO, Devic syndrome) is an inflammatory disorder of the central nervous system of putative autoimmune etiology that primarily affects the optic nerves and spinal cord. NMO is frequently associated with immunoglobulin G (IgG) antibodies to aquaporin-4 (AQP4-IgG), which are thought to be involved in the patho-genesis of the disease. The frequency and diagnostic relevance of immunoglobulin M (IgM) antibodies to aquaporin-4 (AQP4-IgM) in patients with NMO is essentially not known. Testing for AQP4-IgM may be of importance since 20%-30% of patients with NMO are negative for AQP4-IgG. Moreover, IgM antibodies are more potent activators of complement compared with IgG, and are detectable at NMO lesional sites.

METHODS

Serum samples from 42 patients with NMO spectrum disorders (NMOSD) and from 66 controls were tested for IgM AQP4-Ab using a cell-based assay employing HEK293 cells transfected with human full length AQP4. To control for possible interactions between IgG and IgM, serum was depleted of IgG prior to testing by indirect immunofluorescence.

RESULTS

IgM AQP4-Ab were detectable in 4/42 samples from patients with NMOSD, but in none of the 66 control samples. In three patients, titers were higher following depletion of total IgG from the samples. One sample was positive only after precipitation of total IgG.

CONCLUSIONS

AQP4 antibodies of the IgM class exist in almost 10% of patients with NMO and might contribute to lesion pathology. Routine testing for AQP4-IgM appears to not be justified, as all AQP4-IgM positive patients were also positive for AQP4-IgG, and none of the AQP4-IgG negative samples were positive for AQP4-IgM.

Aquaporins and neurodegenerative diseases

Aquaporins (AQPs) are a family of widely distributed membrane-inserted water channel proteins providing a pathway for osmotically-driven water, glycerol, urea or ions transport through cell membranes and mechanisms to control particular aspects of homeostasis. Beside their physiological expression patterns in Central Nervous System (CNS), it is conceivable that AQPs are also abnormally expressed in some pathological conditions interesting CNS (e.g. neurodegenerative diseases) in which preservation of brain homeostasis is at risk.The purpose of this review was to take in consideration those neurodegenerative diseases in whose pathogenetic processes it was possible to hypothesize some alterations in CNS AQPs expression or modulation leading to damages of brain water homeostasis.

Patterns of antibody binding to aquaporin-4 isoforms in neuromyelitis optica

Background

Neuromyelitis optica (NMO), a severe demyelinating disease, represents itself with optic neuritis and longitudinally extensive transverse myelitis. Serum NMO-IgG autoantibodies (Abs), a specific finding in NMO patients, target the water channel protein aquaporin-4 (AQP4), which is expressed as a long (M-1) or a short (M-23) isoform.

Methodology/Principal Findings

The aim of this study was to analyze serum samples from patients with NMO and controls for the presence and epitope specificity of IgG and IgM anti-AQP4 Abs using an immunofluorescence assay with HEK293 cells expressing M-1 or M-23 human AQP4. We included 56 patients with definite NMO (n = 30) and high risk NMO (n = 26), 101 patients with multiple sclerosis, 27 patients with clinically isolated syndromes (CIS), 30 patients with systemic lupus erythematosus (SLE) or Sjögren's syndrome, 29 patients with other neurological diseases and 47 healthy controls. Serum anti-AQP4 M-23 IgG Abs were specifically detected in 29 NMO patients, 17 patients with high risk NMO and two patients with myelitis due to demyelination (CIS) and SLE. In contrast, IgM anti-AQP4 Abs were not only found in some NMO and high risk patients, but also in controls. The sensitivity of the M-23 AQP4 IgG assay was 97% for NMO and 65% for high risk NMO, with a specificity of 100% compared to the controls. Sensitivity with M-1 AQP4 transfected cells was lower for NMO (70%) and high risk NMO (39%). The conformational epitopes of M-23 AQP4 are the primary targets of NMO-IgG Abs, whereas M-1 AQP4 Abs are developed with increasing disease duration and number of relapses.

Conclusions

Our results confirm M-23 AQP4-IgG Abs as reliable biomarkers in patients with NMO and high risk syndromes. M-1 and M-23 AQP4-IgG Abs are significantly associated with a higher number of relapses and longer disease duration.