Related Articles

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.

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.

Background

Neuromyelitis optica (NMO) is a demyelinating disease of the central nervous system (CNS) of putative autoimmune aetiology. Early discrimination between multiple sclerosis (MS) and NMO is important, as optimum treatment for both diseases may differ considerably. Recently, using indirect immunofluorescence analysis, a new serum autoantibody (NMO-IgG) has been detected in NMO patients. The binding sites of this autoantibody were reported to colocalize with aquaporin 4 (AQP4) water channels. Thus we hypothesized that AQP4 antibodies in fact characterize NMO patients.

Methods and Findings

Based on these observations we cloned human water channel AQP4, expressed the protein in a eukaryotic transcription/translation system, and employed the recombinant AQP4 to establish a new radioimmunoprecipitation assay (RIPA). Indeed, application of this RIPA showed that antibodies against AQP4 exist in the majority of patients with NMO (n = 37; 21 positive) as well as in patients with isolated longitudinally extensive transverse myelitis (n = 6; six positive), corresponding to a sensitivity of 62.8% and a specificity of 98.3%. By contrast, AQP4 antibodies were virtually absent in 291 other participants, which included patients with MS (n = 144; four positive), patients with other inflammatory and noninflammatory neurological diseases (n = 73; one positive), patients with systemic autoimmune diseases (n = 45; 0 positive), and healthy participants (n = 29; 0 positive).

Conclusions

In the largest series reported so far to our knowledge, we quantified AQP4 antibodies in patients with NMO versus various other diseases, and showed that the aquaporin 4 water channel is a target antigen in a majority of patients with NMO. The newly developed assay represents a highly specific, observer-independent, and easily reproducible detection method facilitating clinically relevant discrimination between NMO, MS, and other inflammatory diseases.

A newly developed method to detect antibodies to the aquaporin 4 water channel can help discriminate between neuromyelitis optica, multiple sclerosis, and other inflammatory diseases.

Editors' Summary

Background.

Neuromyelitis optica (NMO or Devic syndrome) is a rare disease in which the immune system destroys the myelin (fatty material that insulates nerve fibers so that the body and the brain can communicate using electrical messages) in the optic nerve and spinal cord. Myelin destruction (demyelination) in these parts of the central nervous system (CNS) causes pain and swelling (inflammation) of the optic nerve (optic neuritis) and spinal cord (myelitis). The resultant disruption of communication along these nerves means that patients with NMO experience temporary or permanent blindness in one or both eyes that is preceded or followed by limb weakness or paralysis and loss of bladder and bowel control. These two sets of symptoms can occur many months apart and may happen once during a person's lifetime or recur at intervals. There is no cure for NMO, but corticosteroids or plasmapheresis reduce inflammation during acute attacks and, because NMO is an autoimmune disease (one in which the immune system attacks the body's own tissues instead of foreign organisms), long-term immunosuppression may prevent further attacks.

Why Was This Study Done?

There are many inflammatory/demyelinating diseases of the CNS with clinical symptoms similar to those of NMO. It is particularly hard to distinguish between NMO and multiple sclerosis, an autoimmune disease that involves widespread demyelination. Neurologists need to make a correct diagnosis before starting any treatment and usually use clinical examination and magnetic resonance imaging (to detect sites of inflammation) to help them in this task. Recently, however, a biomarker for NMO was identified. Many patients with NMO make autoantibodies (proteins that recognize a component of a person's own tissues) called NMO-IgGs. These recognize aquaporin 4 (AQP4), a protein that allows water to move through cell membranes. It is not known how often patients with NMO or other demyelinating diseases make antibodies to AQP4, so it is unclear whether testing for these antibodies would help in the diagnosis of NMO. In this study, the researchers have developed a new assay for antibodies to AQP4 and then quantified the antibodies in patients with NMO and other demyelinating diseases.

What Did the Researchers Do and Find?

The researchers made radioactively labeled AQP4 in a test tube, then incubated samples of this with serum (the liquid portion of blood), added small beads coated with protein A (a bacterial protein that binds to antibodies) and allowed the beads to settle. The amount of radioactivity attached to the beads indicates the amount of antibody to AQP4 in the original serum. The researchers used this radioimmunoprecipitation assay to measure antibodies to AQP4 in sera from 37 patients with NMO and from six with another neurological condition, longitudinally extensive transverse myelitis (LETM), which is characterized by large demyelinated lesions across the width of the spinal cord but no optic neuritis; these patients often develop NMO. They also measured antibodies to AQP4 in the sera of nearly 300 other people including patients with multiple sclerosis, other neurological conditions, various autoimmune diseases, and healthy individuals. Nearly two-thirds of the patients with NMO and all those with LETM made antibodies against AQP4; very few of the other study participants made these antibodies. In particular, only four of the 144 patients with multiple sclerosis made AQP4 antibodies.

What Do These Findings Mean?

These findings indicate that testing for antibodies to AQP4 could help neurologists distinguish between NMO and multiple sclerosis and between NMO and other demyelinating diseases of the CNS. In addition, the new radioimmunoprecipitation assay provides a standardized, high-throughput way to quantitatively test for these antibodies, whereas the indirect immune fluorescence assay for measurement of unspecific NMO-IgG is observer-dependent and nonquantitative. Although these findings need to be confirmed in more patients and the assay's reliability demonstrated in different settings, the measurement of antibodies to AQP4 by radioimmunoprecipitation may become a standard part of the differential diagnosis of NMO. Additional research will determine whether AQP4 is the only protein targeted by autoantibodies in NMO and whether this targeting is a critical part of the disease process.

Additional Information.

Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040133.

US National Institute of Neurological Disorders and Stroke has information for patients who have neuromyelitis optica, transverse myelitis, and multiple sclerosis

The Transverse Myelitis Association offers information and useful links for patients and their carers about transverse myelitis and neuromyelitis optica (in several languages, including English and Spanish)

Mayo Clinic information for patients on Devic's syndrome

Medline Plus encyclopedia pages discuss autoimmune disorders (in English and Spanish)

A brief overview of aquaporins is available from the University of Miami

The American MS Society has information on MS

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.

Background and Purpose

Although plasmapheresis is becoming standard practice as a rescue therapy for neuromyelitis optica (NMO), evidence for the therapeutic efficacy of plasmapheresis is limited, and the effect of plasmapheresis on anti-aquaporin-4 (AQP4) levels in patients with NMO has not been reported. Here, our objective was to evaluate the clinical efficacy of therapeutic plasmapheresis and its effect on anti-AQP4 antibody levels in patients with NMO spectrum disorder (NMOSD).

Methods

We retrospectively reviewed the medical records of 15 patients with NMOSD who had 18 acute attacks and received plasmapheresis because they did not respond to high-dose intravenous methylprednisolone (IVMP) therapy. Anti-AQP4 antibodies were measured before and after plasmapheresis. The primary outcomes were functional improvements immediately and 6 months after plasmapheresis, and the secondary outcome was the change in anti-AQP4 antibody serum levels following plasmapheresis.

Results

Plasmapheresis following IVMP therapy led to significant improvement in 50% of the 18 attacks in 15 patients immediately after the procedure was completed, and in 78% (14 attacks) after 6 months. Plasmapheresis was generally well tolerated in all patients. Anti-AQP4 antibody serum levels declined significantly following plasmapheresis, to a mean of 15% of the preplasmapheresis levels. Lower scores on the visual outcome scale recorded before an attack were associated with significant immediate improvement upon the completion of plasmapheresis (p=0.03).

Conclusions

Plasmapheresis following IVMP therapy effectively removed anti-AQP4 antibodies and was accompanied by a substantial improvement in the neurological disability of patients with NMOSD. Lower levels of pre-existing neurological damage may be associated with an improved acute response to plasmapheresis.

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.

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.

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.

Background

The aquaporin-4-specific serum autoantibody, NMO-IgG, is a validated biomarker distinguishing neuromyelitis optica spectrum disorders (NMOSD) from multiple sclerosis (MS). Because fulminant attacks are more common in NMOSD than MS, some suggest that NMO-IgG may be a marker of destructive demyelination rather than a disease-specific biomarker. This study is the first to compare NMO-IgG serostatus among patients with fulminant CNS-inflammatory demyelinating disease (CNS-IDD).

Objective

To determine if NMO-IgG distinguishes NMOSD from other fulminant, steroid-refractory CNS-IDDs.

Design

Descriptive historical cohort

Setting

Neuroimmunology Laboratory and Neurology Practice, Mayo Clinic.

Patients and Methods

Sera from 74 patients plasmapheresed between 1993 and 2007 for a steroid-refractory CNS-IDD were tested for NMO-IgG (by indirect immunofluorescence assay). Two blinded observers scored sera (tested at 1:120 dilution). Clinical data were obtained by medical record review.

Results

Pre-plasmapheresis sera were available from 74 patients (F:M =2.5 ); mean time from blood draw to plasmapheresis was 13 days. At plasmapheresis, mean age was 46 years (range, 7 to 8 0); mean EDSS was 7 (range, 3.5 to 9.5) and diagnoses were NMO (14), longitudinally extensive transverse myelitis (LETM; ≥ 3 vertebral segments; 20), transverse myelitis (TM; < 3 vertebral segments; 8), acute disseminated encephalomyelitis (ADEM; 1), MS (definite, 18; probable, 11), and optic neuritis (ON; 2). NMO-IgG was detected in 20 patients (27%): 9 NMO, 10 LETM and one recurrent ON, and in no patient with fulminant ADEM, MS, TM or monophasic ON.

Conclusions

NMO-IgG is a specific biomarker for NMOSD and is not simply a marker of destructive CNS-IDD.

Introduction

The seroprevalence of human T-cell leukemia virus type 1 (HTLV-1) is very high among Brazilians (∼1∶200). HTLV-1 associated myelopathy or tropical spastic paraparesis (HAM/TSP) is the most common neurological complication of HTLV-1 infection. HAM/TSP can present with an acute/subacute form of longitudinally extensive myelitis, which can be confused with lesions seen in aquaporin-4 antibody (AQP4-Ab) positive neuromyelitis optica spectrum disorders (NMOSD) on MRI. Moreover, clinical attacks in patients with NMOSD have been shown to be preceded by viral infections in around 30% of cases.

Objective

To evaluate the frequency of AQP4-Ab in patients with HAM/TSP. To evaluate the frequency of HTLV-1 infection in patients with NMOSD.

Patients and Methods

23 Brazilian patients with HAM/TSP, 20 asymptomatic HTLV-1+ serostatus patients, and 34 with NMOSD were tested for AQP4-Ab using a standardized recombinant cell based assay. In addition, all patients were tested for HTLV-1 by ELISA and Western blotting.

Results

20/34 NMOSD patients were positive for AQP4-Ab but none of the HAM/TSP patients and none of the asymptomatic HTLV-1 infected individuals. Conversely, all AQP4-Ab-positive NMOSD patients were negative for HTLV-1 antibodies. One patient with HAM/TSP developed optic neuritis in addition to subacute LETM; this patient was AQP4-Ab negative as well. Patients were found to be predominantly female and of African descent both in the NMOSD and in the HAM/TSP group; Osame scale and expanded disability status scale scores did not differ significantly between the two groups.

Conclusions

Our results argue both against a role of antibodies to AQP4 in the pathogenesis of HAM/TSP and against an association between HTLV-1 infection and the development of AQP4-Ab. Moreover, the absence of HTLV-1 in all patients with NMOSD suggests that HTLV-1 is not a common trigger of acute attacks in patients with AQP4-Ab positive NMOSD in populations with high HTLV-1 seroprevalence.

Objective:

To asses the presence of cortical demyelination in brains of patients with neuromyelitis optica (NMO). NMO is an autoimmune inflammatory demyelinating disease that specifically targets aquaporin-4-rich regions of the CNS. Since aquaporin-4 is highly expressed in normal cortex, we anticipated that cortical demyelination may occur in NMO.

Methods:

This is a cross-sectional neuropathologic study performed on archival forebrain and cerebellar tissue sections from 19 autopsied patients with a clinically and/or pathologically confirmed NMO spectrum disorder.

Results:

Detailed immunohistochemical analyses of 19 archival NMO cases revealed preservation of aquaporin-4 in a normal distribution within cerebral and cerebellar cortices, and no evidence of cortical demyelination.

Conclusions:

This study provides a plausible explanation for the absence of a secondary progressive clinical course in NMO and shows that cognitive and cortical neuroimaging abnormalities previously reported in NMO cannot be attributed to cortical demyelination. Lack of cortical demyelination is another characteristic that further distinguishes NMO from MS.

GLOSSARY

= aquaporin-4;

= blood-brain barrier;

= immunoglobulin G;

= multiple sclerosis;

= neuromyelitis optica;

= neuromyelitis optica spectrum disorder.

Objective:

To evaluate the prevalence of aquaporin-4 (AQP4) antibody in Thai patients with idiopathic inflammatory demyelinating CNS diseases (IIDCDs) and to analyze the significance of the autoantibody to distinguish neuromyelitis optica (NMO) and other NMO spectrum disorders (ONMOSDs) from other IIDCDs, especially multiple sclerosis (MS).

Methods:

We retrospectively evaluated 135 consecutive patients with IIDCDs seen at the MS clinic at Siriraj Hospital, Bangkok, Thailand, and classified them into NMO, ONMOSDs, optic-spinal MS (OSMS), classic MS (CMS), and clinically isolated syndrome (CIS) groups in this order with accepted diagnostic criteria. The patients' coded sera were tested separately for AQP4 antibody. Then the relations between the clinical diagnosis and the AQP4 antibody serologic status were analyzed.

Results:

Among the 135 patients, 53 (39.3%) were AQP4 antibody–positive. Although the AQP4 antibody–positive group had features of NMO, such as female predominance, long cord lesions (>3 vertebral bodies), and CSF pleocytosis, only 18 patients (33% of 54) fully met Wingerchuk 2006 criteria except for AQP4 antibody–seropositive status. We also detected some AQP4 antibody–positive patients in the OSMS (4 of 7), CMS (11 of 46), and CIS (1 of 16) groups. These patients had been misdiagnosed with MS because they often had brain lesions and never underwent spinal cord MRI examination or lacked long cord lesions.

Conclusions:

AQP4 antibody was highly prevalent (almost 40%) in Thai patients with IIDCDs. Moreover, only one-third of AQP4 antibody–positive patients fully met Wingerchuk 2006 criteria, and many were misdiagnosed with MS. A sensitive AQP4 antibody assay is required in this region because the therapy for NMO is different from that for MS.

Neuromyelitis optica (NMO) is an idiopathic inflammatory disorder of the central nervous system (CNS) that preferentially affects the optic nerves and spinal cord. In Asia, NMO has long been considered a subtype of multiple sclerosis (MS). However, recent clinical, pathological, immunological, and imaging studies have suggested that NMO is distinct from MS. This reconsideration of NMO was initially prompted by the discovery of a specific antibody for NMO (NMO-IgG) in 2004. NMO-IgG is an autoantibody that targets aquaporin-4 (AQP4), the most abundant water channel in the CNS; hence, it was named anti-AQP4 antibody. Since it demonstrated reasonable sensitivity and high specificity, anti-AQP4 antibody was incorporated into new diagnostic criteria for NMO.The spectrum of NMO is now known to be wider than was previously recognized and includes a proportion of patients with recurrent, isolated, longitudinally extensive myelitis or optic neuritis, and longitudinally extensive myelitis or optic neuritis associated with systemic autoimmune disease or with brain lesions typical of NMO. In this context, a new concept of "NMO spectrum disorders" was recently introduced. Furthermore, seropositivity for NMO-IgG predicts future relapses and is recognized as a prognostic marker for NMO spectrum disorders. Humoral immune mechanisms, including the activation of B-cells and the complement pathway, are considered to play important roles in NMO pathogenesis. This notion is supported by recent studies showing the potential pathogenic role of NMO-IgG as an initiator of NMO lesions. However, a demonstration of the involvement of NMO-IgG by the development of active immunization and passive transfer in animal models is still needed. This review focuses on the new concepts of NMO based on its pathophysiology and clinical characteristics. Potential management strategies for NMO in light of its pathomechanism are also discussed.

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.

Neuromyelitis optica (NMO) is a severe inflammatory CNS disorder of putative autoimmune aetiology, which predominantly affects the spinal cord and optic nerves. Recently, a highly specific serum reactivity to CNS microvessels, subpia and Virchow–Robin spaces was described in patients with NMO [called NMO–IgG (NMO–immunoglobulin G)]. Subsequently, aquaporin-4 (AQP4), the most abundant water channel in the CNS, was identified as its target antigen. Strong support for a pathogenic role of the antibody would come from studies demonstrating a correlation between AQP4-Ab (AQP4-antibody) titres and the clinical course of disease. In this study, we determined AQP4-Ab serum levels in 96 samples from eight NMO–IgG positive patients (median follow-up 62 months) in a newly developed fluorescence-based immunoprecipitation assay employing recombinant human AQP4. We found that AQP4-Ab serum levels correlate with clinical disease activity, with relapses being preceded by an up to 3-fold increase in AQP4-Ab titres, which was not paralleled by a rise in other serum autoantibodies in one patient. Moreover, AQP4-Ab titres were found to correlate with CD19 cell counts during therapy with rituximab. Treatment with immunosuppressants such as rituximab, azathioprine and cyclophosphamide resulted in a marked reduction in antibody levels and relapse rates. Our results demonstrate a strong relationship between AQP4-Abs and clinical state, and support the hypothesis that these antibodies are involved in the pathogenesis of NMO.

Neuromyelitis optica (NMO) is an inflammatory demyelinating disorder of the central nervous system that has been thought to be a severe subtype of multiple sclerosis for a long time. The discovery of aquaporin-4 (AQP4) antibody as a highly specific marker responsible for the pathogenesis of NMO, not only has made a revolutionary pace in establishing a serologic distinction between the two diseases, but it has also classified NMO as an antibody-mediated disorder. Similarly, myasthenia gravis (MG) is a well-known antibody-mediated disorder. In this report, we describe the case of a middle-aged female patient who experienced definite MG with an unclear clinical picture of chronic demyelinating disease that initially reflected the diagnosis of MS, but further imaging and paraclinical workup (e.g. positive AQP4 antibody test) revealed NMO. The coexistence of NMO and MG is previously described. However, this is the first case with NMO symptoms preceding the onset of MG. Of note, the development of MG occurred after a 2-year period of interferon β-1b (IFN β-1b) administration. This calls the question to mind of whether in our case MG is induced by the administration of interferon, instead of an original pathogenic link between MG and NMO. In other words, immunomodulatory treatments can slip the immunity towards T-helper II predominant pathways that can trigger MG. However, if we assume that such an explanation (i.e. increased susceptibility to autoantibody-mediated disorders) is true, our case can be considered the first case of NMO who developed MG following IFN β-1b treatment.

Background

Anti‐aquaporin 4 (AQP4) antibodies were found in patients with neuromyelitis optica (NMO) and Japanese optic–spinal multiple sclerosis (OSMS).

Objective

To review the clinical features and investigate anti‐AQP4 antibodies of Japanese patients with multiple sclerosis (MS), with or without long spinal cord lesions (LCL).

Methods

Anti‐AQP4 antibodies were examined in the sera of 128 consecutive Japanese patients by the immunofluorescence method using AQP4 transfected cells.

Results

The 45 LCL‐MS patients included 28 with a long spinal cord lesion extending contiguously over three vertebral segments on sagittal T2 weighted images (long T2 lesion) and 17 with segmental cord atrophy extending more than three vertebral segments. We identified 25 patients with anti‐AQP4 antibody with LCL and anti‐AQP4 antibody. Anti‐AQP4 antibody was found in 12/17 (70.6%) LCL‐MS patients with segmental cord atrophy, and in 13/28 (46.4%) LCL‐MS patients without segmental long cord atrophy (p = 0.135, Fisher's exact test). Seropositive MS patients with LCL had more relapses than seronegative patients (p = 0.0004, Mann–Whitney U test). 9 patients with OSMS were negative for anti‐AQP4 antibody who did not show LCL.

Conclusion

These results suggest that an anti‐AQP4 antibody is found not only in MS patients with long T2 lesions but also in patients with segmental cord atrophy extending more than three vertebral segments. It is a marker of LCL‐MS showing frequent exacerbations. Japanese OSMS cases comprised those that were identical to NMO cases and those that were more closely related to classic MS.

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.

Neuromyelitis optica (NMO) is an idiopathic inflammatory syndrome of the central nervous system that is characterized by severe attacks of optic neuritis (ON) and myelitis. Until recently, NMO was considered a disease without brain involvement. However, since the discovery of NMO-IgG/antiaqaporin-4 antibody, the concept of NMO was broadened to NMO spectrum disorder (NMOSD), and brain lesions are commonly recognized. Furthermore, some patients present with brain symptoms as their first manifestation and develop recurrent brain symptoms without ON or myelitis. Brain lesions with characteristic locations and configurations can be helpful in the diagnosis of NMOSD. Due to the growing recognition of brain abnormalities in NMOSD, these have been included in the NMO and NMOSD diagnostic criteria or guidelines. Recent technical developments such as diffusion tensor imaging, MR spectroscopy, and voxel-based morphometry reveal new findings related to brain abnormalities in NMOSD that were not identified using conventional MRI. This paper focuses on the incidence and characteristics of the brain lesions found in NMOSD and the symptoms that they cause. Recent studies using advanced imaging techniques are also introduced.

Background:

Optic neuritis (ON) can be the first presentation of multiple sclerosis (MS) or neuromyelitis optica (NMO). Anti-aquaporin-4 IgG (AQP4 IgG) is a highly specific and moderately sensitive biomarker for NMO. This study was designed to assess the rate of seropositivity for AQP4 IgG, and the short-term outcome of patients presenting with single isolated ON (SION).

Methods:

A cohort of 41 consecutive patients experiencing severe (< 20 / 200) SION (not fulfilling the diagnostic criteria for MS or NMO), was prospectively recruited. Blood sampling was carried out immediately after the diagnosis of ON, and AQP4 IgG was tested qualitatively, using an indirect immunofluorescence kit. After clinical and paraclinical investigations, all the patients were followed up for a short-term period of at least 18 months.

Results:

The seroprevalence among the initial ON patients was 9.7% (4 / 41). The short-term conversion rate to MS and NMO was estimated to be about 7.3 and 4.9%, respectively. The conversion rate to NMO in initially seropositive patients was greater than that for the whole cohort [2 / 4 (50%) vs. 2 / 41 (4.9%); P = 0.035; Odds ratio: 19.5, 95% confidence interval: 1.73 to 219.50].

Conclusion:

AQP4 IgG seropositive SION patients were more likely to develop NMO in comparison to the total SION population. Further studies, with a longer follow-up period and larger sample sizes are warranted to assess the clinical and prognostic value of assessing AQP4 IgG in SION.

Neuromyelitis optica (NMO) is a rare autoimmune disorder, distinct from multiple sclerosis, causing inflammatory lesions in the optic nerves and spinal cord. An autoantibody (NMO IgG) against aquaporin-4 (AQP4), a water channel expressed on astrocytes is thought to be causative. Peripheral production of the antibody is triggered by an unknown process in genetically susceptible individuals. Anti-AQP4 antibody enters the central nervous system (CNS) when the blood brain barrier is made permeable and has high affinity for orthogonal array particles of AQP4. Like other autoimmune diseases, Th17 cells and their effector cytokines (such as interleukin 6) have been implicated in pathogenesis. AQP4 expressing peripheral organs are not affected by NMO IgG, but the antibody causes extensive astrocytic loss in specific regions of the CNS through complement mediated cytotoxicity. Demyelination occurs during the inflammatory process and is probably secondary to oligodendrocyte apoptosis subsequent to loss of trophic support from astrocytes. Ultimately, extensive axonal injury leads to severe disability. Despite rapid advances in the understanding of NMO pathogenesis, unanswered questions remain, particularly with regards to disease mechanisms in NMO IgG seronegative cases. Increasing knowledge of the molecular pathology is leading to improved treatment strategies.

Objective

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease of the central nervous system. Circulating autoantibodies (NMO-IgG) against astrocyte water channel aquaporin-4 (AQP4) cause complement- and cell-mediated astrocyte damage with consequent neuroinflammation and demyelination. Current NMO therapies, which have limited efficacy, include immunosuppression and plasma exchange. The objective of this study was to develop a potential new NMO therapy based on blocking of pathogenic NMO-IgG to its target, AQP4.

Methods

We generated non-pathogenic recombinant monoclonal anti-AQP4 antibodies that selectively block NMO-IgG binding to AQP4. These antibodies comprise a tight-binding anti-AQP4 Fab and a mutated Fc that lacks functionality for complement- and cell-mediated cytotoxicity. The efficacy of the blocking antibodies was studied using cell culture, spinal cord slice and in vivo mouse models of NMO.

Results

In AQP4-expressing cell cultures, the non-pathogenic competing antibodies blocked binding of NMO-IgG in human sera, reducing to near zero complement- and cell-mediated cytotoxicity. The antibodies prevented the development of NMO lesions in an ex vivo spinal cord slice model of NMO and in an in vivo mouse model, without causing cytotoxicity.

Interpretation

Our results provide proof-of-concept for therapy of NMO with blocking antibodies. The broad efficacy of antibody inhibition is likely due to steric competition because of its large physical size compared to AQP4. Blocker therapy to prevent binding of pathogenic autoantibodies to their targets may be useful for treatment of other autoimmune diseases as well.

Introduction

Optic neuritis, although uncommon, can be the initial presentation of Sjögren’s syndrome. Coexisting Sjögren’s syndrome has also been reported with neuromyelitis optica spectrum disorder. This case report highlights the association between the two diseases and the importance of rheumatological and neurological evaluations in patients with such diagnoses. Distinction of neuromyelitis optica with coexisting connective tissue disease has both prognostic and therapeutic significance for the patient.

Case presentation

We report a case of a 56-year-old Chinese woman who presented with bilateral asymmetric visual loss secondary to optic neuritis. She was subsequently found to be seropositive for neuromyelitis optica immunoglobulin G (NMO-IgG) (anti-aquaporin-4 antibody) and was diagnosed with neuromyelitis optica spectrum disorder. She also fulfilled the international criteria for Sjögren’s syndrome. Despite initial high dose immunosuppressive therapy, she failed to regain vision in one eye.

Conclusion

Patients presenting with optic neuritis and severe visual loss should be screened for neuromyelitis optica and treated appropriately. Neuromyelitis optica has been associated with systemic autoimmune diseases, in particular Sjögren’s syndrome, and current evidence indicates that they are two distinct entities. We recommend that both diagnoses be considered in cases of optic neuritis with severe visual loss.

Neuromyelitis optica (NMO)-immunoglobulin G (IgG) is a clinically validated serum biomarker that distinguishes relapsing central nervous system (CNS) inflammatory demyelinating disorders related to NMO from multiple sclerosis. This autoantibody targets astrocytic aquaporin-4 (AQP4) water channels. Clinical, radiological, and immunopathological data suggest that NMO-IgG might be pathogenic. Characteristic CNS lesions exhibit selective depletion of AQP4, with and without associated myelin loss; focal vasculocentric deposits of IgG, IgM, and complement; prominent edema; and inflammation. The effect of NMO-IgG on astrocytes has not been studied. In this study, we demonstrate that exposure to NMO patient serum and active complement compromises the membrane integrity of CNS-derived astrocytes. Without complement, astrocytic membranes remain intact, but AQP4 is endocytosed with concomitant loss of Na+-dependent glutamate transport and loss of the excitatory amino acid transporter 2 (EAAT2) . Our data suggest that EAAT2 and AQP4 exist in astrocytic membranes as a macromolecular complex. Transport-competent EAAT2 protein is up-regulated in differentiating astrocyte progenitors and in nonneural cells expressing AQP4 transgenically. Marked reduction of EAAT2 in AQP4-deficient regions of NMO patient spinal cord lesions supports our immunocytochemical and immunoprecipitation data. Thus, binding of NMO-IgG to astrocytic AQP4 initiates several potentially neuropathogenic mechanisms: complement activation, AQP4 and EAAT2 down-regulation, and disruption of glutamate homeostasis.

Background

Antibodies to the water channel protein aquaporin-4 (AQP4), which is expressed in astrocytic endfeet at the blood brain barrier, have been identified in the serum of Neuromyelitis optica (NMO) patients and are believed to induce damage to astrocytes. However, AQP4 specific T helper cell responses that are required for the generation of anti-AQP4 antibodies and most likely also for the formation of intraparenchymal CNS lesions have not been characterized.

Methodology/Principal Findings

Using overlapping 15-meric peptides of AQP4, we identified the immunogenic T cell epitopes of AQP4 that are restricted to murine major histocompatibility complex (MHC) I-Ab. The N-terminal region of AQP4 was highly immunogenic. More precisely, the intracellular epitope AQP422–36 was detected as major immunogenic determinant. AQP482–108 (located in the second transmembrane domain), AQP4139–153 (located in the second extracellular loop), AQP4211–225 (located in the fifth transmembrane domain), AQP4235–249 (located in the sixth transmembrane domain), as well as AQP4289–306 in the intracellular C-terminal region were also immunogenic epitopes. AQP422–36 and AQP4289–303 specific T cells were present in the natural T cell repertoire of wild type C57BL/6 mice and T cell lines were raised. However, active immunization with these AQP4 peptides did not induce signs of spinal cord disease. Rather, sensitization with AQP4 peptides resulted in production of IFN-γ, but also IL-5 and IL-10 by antigen-specific T cells. Consistent with this cytokine profile, the AQP4 specific antibody response upon immunization with full length AQP4 included IgG1 and IgG2, which are associated with a mixed Th2/Th1 T cell response.

Conclusions and Significance

AQP4 is able to induce an autoreactive T cell response. The identification of I-Ab restricted AQP4 specific T cell epitopes will allow us to investigate how AQP4 specific autoimmune reactions are regulated and to establish faithful mouse models of NMO that include both cellular and humoral responses against AQP4.