Utility of aquaporin-4 antibody assay in patients with neuromyelitis optica spectrum disorders

Autoimmune Movement Disorders

OBJECTIVE

This article reviews the clinical and antibody spectrum of autoimmune cerebellar ataxia and other autoimmune movement disorders. It highlights characteristic phenotypes and red flags to the diagnosis and how these rare, but treatable, disorders are integrated into a differential diagnosis.

LATEST DEVELOPMENTS

An increasing number of neuronal antibodies have been identified in patients with cerebellar ataxia, for example, against Kelch-like protein 11 (KLHL11), seizure-related 6 homolog-like 2, septin-3 and septin-5, or tripartite motif containing protein 9 (TRIM9), TRIM46, and TRIM67. Ig-like cell adhesion molecule 5 (IgLON5) antibody-associated syndromes have emerged as an important alternative diagnostic consideration to various neurodegenerative diseases such as Huntington disease or atypical parkinsonism. Opsoclonus-myoclonus syndrome emerged as the most relevant parainfectious movement disorder related to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

ESSENTIAL POINTS

Autoimmune cerebellar ataxia and other autoimmune movement disorders encompass a broad spectrum of different clinical syndromes, antibodies, and immunopathophysiologic mechanisms. Clinical acumen is key to identifying the cases that should undergo testing for neuronal antibodies. Given the overlap between phenotypes and antibodies, panel testing in serum and CSF is recommended.

Mortality of neuromyelitis optica spectrum disorders in a Chinese population

Objective

Neuromyelitis optica spectrum disorder (NMOSD) is a rapidly disabling disease. Epidemiologic studies have suggested varying NMOSD mortality across ethnic groups. However, NMOSD mortality data in China are scarce. This study’s objectives were to explore mortality and causes of death among Chinese NMOSD patients and to identify independent predictors of death.

Methods

We performed a retrospective study with a 10‐year follow‐up of Chinese NMOSD patients. A Cox proportional hazards model was used to identify independent predictors of death.

Results

Five hundred and sixty‐nine patients were included; 24 patients died during follow‐up, for overall mortality of 4.2%. In these patients, the median disease duration at the time of death was 3.4 years. The most common cause of death was secondary infection (62.5%), especially respiratory infection (45.8%). The second most common cause of death was extensive cervical myelitis with respiratory failure (16.7%). Other causes included suicide (8.3%), cancer (4.2%), cerebral embolism (4.2%), and unknown causes (4.2%). The multivariate Cox analyses indicated that a short first interattack interval (HR = 0.93, 95% CI 0.89–0.98, p = 0.003), lack of regular immunotherapy (HR = 10.34, 95% CI 4.05–26.37, p < 0.001), and older age at onset were independent predictors of death. Every increasing decade of onset age increased the risk of death 2.59 times (95% CI 1.74–3.86, p < 0.001).

Interpretation

Infections were more common in patients not treated with any immunotherapy, indicating that early and consequent immunotherapy might prevent death by infections, which is of great importance for further treatment of NMOSD patients to avoid undertreatment due to fear of treatment‐associated infections.

Comparison of clinical characteristics and prognoses in patients with different AQP4-Ab and MOG-Ab serostatus with neuromyelitis optica spectrum disorders

BACKGROUND

At present, patients positive for aquaporin-4 antibody (AQP4-Ab) or myelin oligodendrocyte glycoprotein antibody (MOG-Ab) are diagnosed as neuromyelitis optica spectrum disorder (NMOSD) and MOG-Ab-associated diseases, respectively. However, some patients who meet the diagnostic criteria for NMOSD and show demyelination of the central nervous system cannot be clearly classified.

METHODS

We performed a prospective cohort study to evaluate the clinical characteristics and prognoses of double-seronegative patients with NMOSD.

RESULTS

A total of 594 patients were included in the cohort, including 26 patients with MOG-Ab, 517 with AQP4-Ab, and 51 with double seronegativity. Compared to AQP4-Ab-positive patients, double-seronegative patients experienced less severe clinical attacks (51.0% vs. 78.1%; P^corr < 0.01), either visual (23.5% vs. 42.6%; P^corr = 0.024) or motor attacks (39.2% vs. 59.8%; P^corr = 0.015), and had a better median Expand Disability Status Scale (EDSS) score at the last follow-up (2.0 vs. 3.0; P^corr = 0.012) and a lower proportion of disability (11.8% vs. 30.9%; P^corr = 0.015). Furthermore, lower risks of visual and motor disability were also observed by Kaplan-Meier analyses (P = 0.031 and 0.038, respectively). Both the MOG-Ab and double-seronegative groups had lower frequencies of severe clinical attacks, especially motor attacks, better EDSS scores at the last visit, and a lower proportion of disability than was found in the AQP4-Ab group (all P values and corrected P values <0.05).

CONCLUSIONS

In patients who met the diagnostic criteria for NMOSD, compared with AQP4-Ab-seropositive patients, double-seronegative and MOG-Ab-seropositive patients had less severe clinical attacks and better prognoses, including lower EDSS scores and a lower proportion of disability.

Pain in NMOSD and MOGAD: A Systematic Literature Review of Pathophysiology, Symptoms, and Current Treatment Strategies

Neuromyelitis optica spectrum disorders (NMOSDs) and myelin oligodendrocyte glycoprotein-antibody-associated disease (MOGAD) are autoimmune inflammatory disorders of the central nervous system (CNS). Pain is highly prevalent and debilitating in NMOSD and MOGAD with a severe impact on quality of life, and there is a critical need for further studies to successfully treat and manage pain in these rare disorders. In NMOSD, pain has a prevalence of over 80%, and pain syndromes include neuropathic, nociceptive, and mixed pain, which can emerge in acute relapse or become chronic during the disease course. The impact of pain in MOGAD has only recently received increased attention, with an estimated prevalence of over 70%. These patients typically experience not only severe headache, retrobulbar pain, and/or pain on eye movement in optic neuritis but also neuropathic and nociceptive pain. Given the high relevance of pain in MOGAD and NMOSD, this article provides a systematic review of the current literature pertaining to pain in both disorders, focusing on the etiology of their respective pain syndromes and their pathophysiological background. Acknowledging the challenge and complexity of diagnosing pain, we also provide a mechanism-based classification of NMOSD- and MOGAD-related pain syndromes and summarize current treatment strategies.

Comprehensive review of neuromyelitis optica and clinical characteristics of neuromyelitis optica patients in Puerto Rico

Neuromyelitis optica (NMO) is an immune-mediated inflammatory disorder of the central nervous system. It is characterized by concurrent inflammation and demyelination of the optic nerve (optic neuritis [ON]) and the spinal cord (myelitis). Multiple studies show variations in prevalence, clinical, and demographic features of NMO among different populations. In addition, ethnicity and race are known as important factors on disease phenotype and clinical outcomes. There are little data on information about NMO patients in underserved groups, including Puerto Rico (PR). In this research, we will provide a comprehensive overview of all aspects of NMO, including epidemiology, environmental risk factors, genetic factors, molecular mechanism, symptoms, comorbidities and clinical differentiation, diagnosis, treatment, its management, and prognosis. We will also evaluate the demographic features and clinical phenotype of NMO patients in PR. This will provide a better understanding of NMO and establish a basis of knowledge that can be used to improve care. Furthermore, this type of population-based study can distinguish the clinical features variation among NMO patients and will provide insight into the potential mechanisms that cause these variations.

Prevalence of anti-aquaporin 4 antibody in a diagnostic cohort of patients being investigated for possible neuromyelitis optica spectrum disorder in Western Australia

OBJECTIVE

To evaluate the prevalence of anti-AQP4 antibody in serum and CSF samples from patients being investigated for possible neuromyelitis optica spectrum disorder (NMOSD) referred to the PathWest State reference laboratory using a sensitive cell-based assay (CBA).

BACKGROUND

NMOSD is an inflammatory CNS disease distinct from MS, which is relatively rare in Western countries. A proportion of patients with NMOSD have detectable serum IgG antibodies that target the water channel aquaporin-4 (AQP4-IgG), but the frequency varies in different populations studied and according to the assay method employed.

METHODS

Sera or CSF from a diagnostic cohort of 196 consecutive patients with possible NMOSD which had previously been screened by indirect immunofluorescence (IIF) on primate cerebellum were re-tested for AQP4-IgG reactivity to the M1 and M23 isoforms of AQP4 using a commercial CBA. A control group of 205 patients with definite MS was also included in the study.

RESULTS

Of the 196 patients, only 5 sera were AQP4-IgG positive, representing 2.6% of patients in the diagnostic cohort. All 5 AQP4-IgG positive patients fulfilled the 2015 revised diagnostic criteria for NMOSD and were females of varied ethnic origins, 4 of whom had longitudinally extensive transverse myelitis. The CBA confirmed AQP4-IgG positivity in the four patients previously reported as positive by IIF, and an additional patient with NMOSD who had previously been diagnosed as MS was also identified. None of the 205 MS sera were AQP4-IgG positive.

CONCLUSIONS

Our study confirms the utility and greater reliability of the M1/M23 CBA for detecting AQP4-IgG in patients with possible NMOSD, and indicates a prevalence of seropositive NMOSD in the Western Australian population similar to that in other Western populations.

Differential diagnosis of neuromyelitis optica spectrum disorders

Neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory disorder of the central nervous system (CNS) mostly manifesting as optic neuritis and/or myelitis, which are frequently recurrent/bilateral or longitudinally extensive, respectively. As the autoantibody to aquaporin-4 (AQP4-Ab) can mediate the pathogenesis of NMOSD, testing for the AQP4-Ab in serum of patients can play a crucial role in diagnosing NMOSD. Nevertheless, the differential diagnosis of NMOSD in clinical practice is often challenging despite the phenotypical and serological characteristics of the disease because: (1) diverse diseases with autoimmune, vascular, infectious, or neoplastic etiologies can mimic these phenotypes of NMOSD; (2) patients with NMOSD may only have limited clinical manifestations, especially in their early disease stages; (3) test results for AQP4-Ab can be affected by several factors such as assay methods, serologic status, disease stages, or types of treatment; (4) some patients with NMOSD do not have AQP4-Ab; and (5) test results for the AQP4-Ab may not be readily available for the acute management of patients. Despite some similarity in their phenotypes, these NMOSD and NMOSD-mimics are distinct from each other in their pathogenesis, prognosis, and most importantly treatment. Understanding the detailed clinical, serological, radiological, and prognostic differences of these diseases will improve the proper management as well as diagnosis of patients.

Gender effect on neuromyelitis optica spectrum disorder with aquaporin4-immunoglobulin G

BACKGROUND

Neuromyelitis optica spectrum disorder with aquaporin4-immunoglobulin G (NMOSD-AQP4) is an inflammatory disease characterised by a high female predominance. However, the effect of gender in patients with NMOSD-AQP4 has not been fully evaluated.

OBJECTIVE

The aim of this study was to determine the effect of gender in clinical manifestations and prognosis of patients with NMOSD-AQP4.

METHODS

The demographics, clinical and radiological characteristics, pattern reversal visual evoked potential (VEP) test results, and prognosis of 102 patients (18 males) with NMOSD-AQP4 were assessed.

RESULTS

Male patients had a higher age at onset (48.7 vs 41 years, p = 0.037) and less optic neuritis as the onset attack (17% vs 44%, p = 0.026), higher tendency to manifest as isolated myelitis over the follow-up period (67% vs 28%, p = 0.005), fewer optic neuritis attacks per year (0.08 vs 0.27, p < 0.001), and shorter relative P100 latency on VEP testing (97.1% vs 108.3%, p = 0.001). Moreover, male gender was significantly associated with the absence of optic neuritis attacks over the follow-up period independent of their age of onset.

CONCLUSION

In NMOSD-AQP4 patients, gender impacts on disease onset age and site of attack. This may be an important clue in identifying NMOSD-AQP4 patients with limited manifestations as well as in predicting their clinical courses.

Accuracy of the Fluorescence-Activated Cell Sorting Assay for the Aquaporin-4 Antibody (AQP4-Ab): Comparison with the Commercial AQP4-Ab Assay Kit

BACKGROUND

The aquaporin-4 antibody (AQP4-Ab) is a disease-specific autoantibody to neuromyelitis optica (NMO). We aimed to evaluate the accuracy of the FACS assay in detecting the AQP4-Ab compared with the commercial cell-based assay (C-CBA) kit.

METHODS

Human embryonic kidney-293 cells were transfected with human aquaporin-4 (M23) cDNA. The optimal cut off values of FACS assay was tested using 1123 serum samples from patients with clinically definite NMO, those at high risk for NMO, patients with multiple sclerosis, patients with other idiopathic inflammatory demyelinating diseases, and negative controls. The accuracy of FACS assay and C-CBA were compared in consecutive 225 samples that were collected between January 2014 and June 2014.

RESULTS

With a cut-off value of MFIi of 3.5 and MFIr of 2.0, the receiver operating characteristic curve for the FACS assay showed an area under the curve of 0.876. Among 225 consecutive sera, the FACS assay and C-CBA had a sensitivity of 77.3% and 69.7%, respectively, in differentiating the sera of definite NMO patients from sera of controls without IDD or of MS. Both assay had a good specificity of 100% in it. The overall positivity of the C-CBA among FACS-positive sera was 81.5%; moreover, its positivity was low as 50% among FACS-positive sera with relatively low MFIis.

CONCLUSIONS

Both the FACS assay and C-CBA are sensitive and highly specific assays in detecting AQP4-Ab. However, in some sera with relatively low antibody titer, FACS-assay can be a more sensitive assay option. In real practice, complementary use of FACS assay and C-CBA will benefit the diagnosis of NMO patients, because the former can be more sensitive among low titer sera and the latter are easier to use therefore can be widely used.

Antibodies to MOG in adults with inflammatory demyelinating disease of the CNS

OBJECTIVE

To evaluate the clinical relevance of myelin oligodendrocyte glycoprotein antibody (MOG-Ab) in a cohort of adults with inflammatory demyelinating disease (IDD) of the CNS.

METHODS

Live cell-based assays for MOG-Ab (IgG1 subset) and antibody to aquaporin-4 (AQP4-Ab) were performed in a cohort of 270 adult patients with IDD and 72 controls. Patients were first grouped by positive antibody result as MOG-Ab or AQP4-Ab, and the remainder were grouped by published diagnostic criteria.

RESULTS

Seventeen patients with IDD (6.3%) had MOG-Abs and 49 patients (18.1%) had AQP4-Abs; none had both antibodies. The MOG-Ab patients predominantly manifested with isolated symptoms of optic neuritis (83%). One-third of these patients experienced relapses, which involved only the optic nerve, and all relapsed within 1 year of disease onset. At onset, MRI in the MOG-Ab group uniquely demonstrated perineural enhancement, extending to the soft tissues around the optic nerves (33%). Although about 30% of MOG-Ab patients had brain MRI lesions, they had fewer periventricular lesions than the 26 patients with relapsing-remitting multiple sclerosis (MS); none of these lesions were ovoid or perpendicular to the ventricle. Moreover, MOG-Ab patients did not meet the diagnostic criteria for definite neuromyelitis optica (NMO) and had less spinal cord involvement than the AQP4-Ab group. Four patients (23.5%) had poor visual outcomes (<0.2) or paraplegia.

CONCLUSIONS

MOG-Abs may be a disease-specific biomarker in adult patients with IDD who have a disease distinct from NMO or MS. The radiologic as well as clinical manifestations of MOG-Ab patients can be useful in their differential diagnosis.

Idiopathic aquaporin-4 antibody negative longitudinally extensive transverse myelitis

Background:

Longitudinally extensive transverse myelitis (LETM) is a characteristic manifestation of neuromyelitis optica (NMO). However, not all patients with LETM are positive for aquaporin-4 (AQP4) antibodies. We evaluated the characteristics of idiopathic isolated LETM negative for AQP4 antibodies.

Methods:

From the National Cancer Center registry of inflammatory diseases of the central nervous system, patients with LETM as an initial manifestation and follow-up for at least two years were enrolled. Their medical records and MRIs were reviewed retrospectively. AQP4 antibody was confirmed by three different validated methods at least three times. Cerebrospinal fluid (CSF) glial fibrillary acidic protein (GFAP) levels were measured to investigate astrocyte damage.

Results:

Among 108 patients with first-ever LETM, 55 were positive for AQP4 antibodies (P-LETM) and 53 were consistently negative. Of them, seven were later diagnosed with seronegative NMO, and four were positive for MOG antibodies. The remaining 42 patients (N-LETM) showed several features distinct from P-LETM: male predominance, older age of onset, milder clinical presentation, spinal cord confinement and absence of combined autoimmunity. CSF GFAP levels were not increased in N-LETM but were markedly elevated in P-LETM.

Conclusions:

Idiopathic isolated N-LETM is not that rare among first-ever LETM, and has many features distinct from P-LETM where astrocytic damage is evident.

Autologous hematopoietic stem cell transplantation in neuromyelitis optica: A registry study of the EBMT Autoimmune Diseases Working Party

Background:

Neuromyelitis optica (NMO) is an inflammatory autoimmune disorder of the central nervous system, hallmarked by pathogenic anti-aquaporin 4 antibodies. NMO prognosis is worse compared with multiple sclerosis.

Objective:

The European Group for Blood and Marrow Transplantation (EBMT) Autoimmune Diseases Working Party (ADWP) conducted a retrospective survey to analyze disease outcome following autologous stem cell transplantation (ASCT).

Methods:

This retrospective multicenter study assessed the efficacy and safety of ASCT in 16 patients suffering from refractory NMO reported to the EBMT registry between 2001 and 2011.

Results:

Fifteen patients were successfully mobilized with cyclophosphamide (Cy) and G-CSF, one with G-CSF alone. All patients received an unmanipulated autologous peripheral blood stem cell graft, after conditioning with BEAM plus anti-thymocyte globulin (ATG, n = 9 patients), thiotepa-Cy ( n = 3) or Cy (200 mg/kg) plus ATG ( n = 4). After a median follow-up of 47 months, three of 16 cases were progression and treatment free, while in the remaining 13 patients further treatments were administered for disability progression or relapse after ASCT. Altogether, relapse-free survival at three and five years was 31% and 10%, respectively, while progression-free survival remained 48% at three and five years.

Conclusions:

In these NMO patients, highly resistant to conventional treatment, ASCT allows for temporary control of the disease, despite a tendency to progress or relapse in the long term.

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.

Characterization of the spectrum of Korean inflammatory demyelinating diseases according to the diagnostic criteria and AQP4-Ab status

Background

The relative frequencies of demyelinating diseases among Korean patients with idiopathic inflammatory demyelinating disease of the central nervous system (IIDD) have not been sufficiently studied. We therefore describe a cohort of 203 patients with IIDD from three centers in Korea whose syndromes were identified precisely according to international clinical criteria and autoantibody to aquaporin 4 (AQP4-Ab) status.

Methods

In total, 260 consecutive patients were screened and 203 were included from three hospitals in Korea. All were tested for AQP4-Ab by using a cell-based assay. Patients who met the criteria for definite neuromyelitis optica (NMO) or had a positive AQP4-Ab test result were defined as the NMO group. Among the others, patients were assessed if they had acute disseminated encephalomyelitis, multiple sclerosis (MS), acute transverse myelitis, optic neuritis, or other demyelinating disease as a clinically isolated syndrome of the brain.

Results

Eighteen percent of patients were classified as the NMO group, 2% as acute disseminated encephalomyelitis, 18% as MS, 41% as acute transverse myelitis, 11% as optic neuritis, and 8% as other clinically isolated syndrome of the brain. AQP4-Ab was positive in 18% of patients and the relative frequency of NMO to MS (NMO/MS ratio) was 1.06. The mean duration of follow up in our patients was 64 months.

Conclusions

Among Korean patients with idiopathic inflammatory demyelinating diseases, the incidence of NMO may be similar to that of MS, and the overall positivity of AQP4-Ab could be lower than previously reported. In addition, acute transverse myelitis that is not associated with MS or NMO can be relatively common in these patients. Further population-based studies with AQP4-Ab are needed to determine the exact incidence of NMO and other idiopathic inflammatory demyelinating diseases in Korea.

Factors associated with the time to next attack in neuromyelitis optica: accelerated failure time models with random effects

BACKGROUND AND OBJECTIVE

Neuromyelitis optica (NMO) is an inflammatory demyelinating disorder of the central nervous system with a relapsing and remitting course. We aimed to identify factors associated with the time to next attack, including the effect of the natural disease course and the diverse treatment regimens, by applying a longitudinal statistical analysis to the individual attacks of each patient.

METHODS

In total, 184 acute attacks among 58 patients with either NMO or NMO spectrum disorder with anti-aquaporin-4 antibody were assessed retrospectively. Patient demographics, clinical characteristics at each attack, and type of treatment during inter-attack periods were assessed. The dependent variable was defined as the time from each attack to the next attack (inter-attack interval). An exponential accelerated failure time model with shared gamma frailty was adapted for statistical analysis.

RESULTS

A multivariable analysis revealed that the time from each attack to the next attack in NMO increased independently by 1.31 times (95% confidence interval (CI), 1.02-1.67; p = 0.035) with each additional cumulative attack experienced, by 5.34 times (95% CI, 1.57-18.13; p = 0.007) with combined azathioprine treatment and continued oral prednisolone, and by 4.26 times (95% CI, 1.09-16.61; p = 0.037) with rituximab treatment.

CONCLUSION

The time to next attack in NMO can increase naturally in the later stages of the disease as the number of cumulative attacks increases. Nevertheless, both combined azathioprine treatment with continued oral prednisolone and rituximab treatment were also associated with a longer time to next attack, independently of the natural disease course of NMO.

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.