Successful Treatment of Refractory Myelin Oligodendrocyte Glycoprotein Antibody–Associated Disease With Tocilizumab: A Case Report and Literature Review

MOG antibody-associated disease after vaccination with ChAdOx1 nCoV-19

To review the demographics and clinical and paraclinical parameters of children with myelin oligodendrocyte glycoprotein (MOG) antibody-associated relapsing disease. In this UK-based, multicentre study, 31 children with MOG antibody-associated relapsing disease were studied retrospectively. Of the 31 children studied, 14 presented with acute disseminated encephalomyelitis (ADEM); they were younger (mean 4.1y) than the remainder (mean 8.5y) who presented with optic neuritis and/or transverse myelitis (p<0.001). Similarly, children who had an abnormal brain magnetic resonance imaging (MRI) at onset (n=20) were younger than patients with normal MRI at onset (p=0.001) or at follow-up (p<0.001). 'Leukodystrophy-like' MRI patterns of confluent largely symmetrical lesions was seen during the course of the disease in 7 out of 14 children with a diagnosis of ADEM, and was only seen in children younger than 7 years of age. Their disability after a 3-year follow-up was mild to moderate, and most patients continued to relapse, despite disease-modifying treatments. MOG antibody should be tested in children presenting with relapsing neurological disorders associated with confluent, bilateral white matter changes, and distinct enhancement pattern. Children with MOG antibody-associated disease present with age-related differences in phenotypes, with a severe leukoencephalopathy phenotype in the very young and normal intracranial MRI in the older children. This finding suggests a susceptibility of the very young and myelinating brain to MOG antibody-mediated mechanisms of damage. Myelin oligodendrocyte glycoprotein (MOG) antibody-associated demyelination manifest with an age-related phenotype. Children with MOG antibody and 'leukodystrophy-like' imaging patterns tend to have poor response to second-line immunotherapy.

Myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD) is a demyelinating disease of the central nervous system (CNS) that manifests as optic neuritis, transverse myelitis, acute disseminated encephalomyelitis, and cortical encephalitis. Some patients with MOGAD present with tumor-like brain lesions. However, hydrocephalus as an initial presentation is rare. We present the case of a 23-year-old Japanese man with an acute onset of headache, nausea, and diplopia, who was initially suspected of having a germinoma but was later diagnosed with MOGAD. Brain magnetic resonance imaging (MRI) revealed a tumor-like lesion with hyperintensity on fluid-attenuated inversion recovery (FLAIR) imaging and contrast enhancement on T1-weighted postcontrast images, extending from the midbrain to the thalamus with obstructive hydrocephalus. Neuroendoscopic third ventriculostomy and brain biopsy were performed. Histopathological analyses revealed demyelination, perivascular lymphocytic infiltration, and MOG loss. MOG antibody tests were positive, confirming MOGAD. The patient was treated with pulse steroid therapy (methylprednisolone 1,000 mg/day) and seven sessions of plasmapheresis, resulting in significant neurological improvement. He was discharged approximately two months after symptom onset, and at the six-month follow-up from discharge, he remained relapse-free with only mild diplopia. In this case, early diagnosis via pathological brain analysis and anti-MOG antibody testing allowed for timely treatment. We emphasize the importance of including MOGAD in the diagnostic workup of tumor-mimicking CNS lesions that can cause hydrocephalus.

Myelin oligodendrocyte glycoprotein (MOG) antibody-associateddisease (MOGAD) is an idiopathic central nervous system (CNS) demyelinating disease gaining recognition with wider availability of cell-based assay (CBA) testing and recently published diagnostic criteria. However, uncertainty remains regarding the interpretation of antibody titers, particularly cerebrospinal fluid (CSF) MOG antibody titers. All MOG IgG CBA results performed by the provincial MitogenDx laboratory in Alberta from July 2017 to July 2023 were retrieved. Chart review was performed in patients with both serum and CSF testing and ≥ 1 positive MOG antibody result. Demographics, antibody titers, clinical and imaging features, treatment, and diagnosis were analyzed based on serum/CSF status. Among 4494 MOG CBA assays, there were 413 CSF samples in 402 patients, and 268 patients had at least one associated serum sample. Mean time between CSF and serum testing was 20.9days (range 0-870days), most with testing within 30days. Five of the 268 patients had serum positive/CSF positive MOG antibodies, 4 with acute disseminated encephalomyelitis and 1 with longitudinally extensive transverse myelitis. Twenty-three patients had serum positive/CSF negative MOG and 13/23 with optic neuritis. CSF MOG antibody positive patients were younger, and more likely to remain MOG seropositive versus CSF negative patients. No seronegative patient had MOG antibodies in CSF. In province-wide testing, CSF MOG antibodies were rare, only in MOG seropositive patients and none with optic neuritis. Our study does not support a clear role for CSF MOG antibody testing in the majority of patients, although further study is required.

Myelin oligodendrocyte glycoprotein (MOG) antibody-associated diseases (MOGAD), which has been recognized as a distinct entity in patients with neuromyelitis optica spectrum disorders, often presents with acute disseminated encephalomyelitis (ADEM) symptoms in pediatric patients. Appropriate treatment based on accurate diagnosis is challenging in relapsing pediatric patients with MOGAD. An 11-year-old girl experienced relapses four times, exhibiting brainstem symptoms, an ADEM episode, seizures, and optic neuritis (ON). She was initially diagnosed with multiple sclerosis and received interferon beta-1a therapy with a mild effect on relapse suppression. She was then transferred from the pediatric department to the department of neurology of our hospital. Two months before her referral visit, she experienced left optic neuritis, and her annualized relapse rate reached 0.6. She desired to switch from the injectable treatment to oral dimethyl fumarate (DMF) administration. At that time, she was found to be seropositive for MOG antibody, but after that had no relapses for more than five years. Moreover, her seropositivity for serum MOG-antibody turned out to be seronegative. DMF showed long-term effects on suppressing relapses in a pediatric patient with MOGAD, revealing its potential as a treatment option for such patients.

Recent reports indicated that myelin oligodendrocyte glycoprotein antibody-associated disease might be a rare complication after severe acute respiratory syndrome coronavirus 2 infection or vaccination. It is unclear whether this is an unspecific sequel of infection or vaccination or caused by possible immunological cross-reactivity of severe acute respiratory syndrome coronavirus 2 proteins and myelin oligodendrocyte glycoprotein. The aim of this study was therefore to elucidate whether there is an immunological cross-reactivity between severe acute respiratory syndrome coronavirus 2 spike or nucleocapsid proteins and myelin oligodendrocyte glycoprotein and to explore the relation of antibody responses against myelin oligodendrocyte glycoprotein and severe acute respiratory syndrome coronavirus 2 and other coronaviruses. We analysed serum samples from patients with severe acute respiratory syndrome coronavirus 2 infection and neurological symptoms with (myelin oligodendrocyte glycoprotein antibody-associated disease, n = 12) or without myelin oligodendrocyte glycoprotein-antibodies (n = 10); severe acute respiratory syndrome coronavirus 2 infection without neurological symptoms (n = 32); vaccinated patients with no history of severe acute respiratory syndrome coronavirus 2 infection and neurological symptoms with (myelin oligodendrocyte glycoprotein antibody-associated disease, n = 10) or without myelin oligodendrocyte glycoprotein-antibodies (n = 9); and severe acute respiratory syndrome coronavirus 2 negative/naïve unvaccinated patients with neurological symptoms with (myelin oligodendrocyte glycoprotein antibody-associated disease, n = 47) or without myelin oligodendrocyte glycoprotein-antibodies (n = 20). All samples were analysed for serum antibody responses to myelin oligodendrocyte glycoprotein, severe acute respiratory syndrome coronavirus 2, and other common coronaviruses (CoV-229E, CoV-HKU1, CoV-NL63 and CoV-OC43). Based on sample amount and antibody titres, 21 samples were selected for analysis of antibody cross-reactivity between myelin oligodendrocyte glycoprotein and severe acute respiratory syndrome coronavirus 2 spike and nucleocapsid proteins using affinity purification and pre-absorption. Whereas we found no association of immunoglobulin G and A myelin oligodendrocyte glycoprotein antibodies with coronavirus antibodies, infections with severe acute respiratory syndrome coronavirus 2 correlated with an increased immunoglobulin M myelin oligodendrocyte glycoprotein antibody response. Purified antibodies showed no cross-reactivity between severe acute respiratory syndrome coronavirus 2 spike protein and myelin oligodendrocyte glycoprotein. However, one sample of a patient with myelin oligodendrocyte glycoprotein antibody-associated disease following severe acute respiratory syndrome coronavirus 2 infection showed a clear immunoglobulin G antibody cross-reactivity to severe acute respiratory syndrome coronavirus 2 nucleocapsid protein and myelin oligodendrocyte glycoprotein. This patient was also seropositive for other coronaviruses and showed immunological cross-reactivity of severe acute respiratory syndrome coronavirus 2 and CoV-229E nucleocapsid proteins. Overall, our results indicate that an immunoglobulin G antibody cross-reactivity between myelin oligodendrocyte glycoprotein and severe acute respiratory syndrome coronavirus 2 proteins is rare. The presence of increased myelin oligodendrocyte glycoprotein-immunoglobulin M antibodies after severe acute respiratory syndrome coronavirus 2 infection may either be a consequence of a previous infection with other coronaviruses or arise as an unspecific sequel after viral infection. Furthermore, our data indicate that myelin oligodendrocyte glycoprotein-immunoglobulin A and particularly myelin oligodendrocyte glycoprotein-immunoglobulin M antibodies are a rather unspecific sequel of viral infections. Finally, our findings do not support a causative role of coronavirus infections for the presence of myelin oligodendrocyte glycoprotein-immunoglobulin G antibodies.

Implications of Low-Titer MOG Antibodies

Myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD) covers a wide spectrum of manifestations and is defined by the presence of MOG seropositivity. However, in a proportion of patients, there may be an overlap in some of the clinical and radiological manifestations between MOGAD and multiple sclerosis (MS). Being wary of this entity is critical to ensure appropriate therapy. Herein, we present a case with recurrent episodes of short-segment myelitis typical for multiple sclerosis, but later diagnosed as MOGAD by MOG antibody seropositivity. This case, along with previous reports, highlights an increasingly recognized subgroup in MOGAD with initial clinical phenotypes suggestive of MS, but later showing a disease course and therapeutic response compatible with MOGAD. Given the potential overlap of some clinical phenotypes in patients with MS and those with MOGAD, we recommend MOG antibody testing in all patients with recurrent short-segment myelitis, conus medullaris involvement, and those who demonstrated steroid dependence.

Aim/backgroundThe concept of neuromyelitis optica spectrum disorder (NMOSD) is changing, with a disease spectrum emerging that includes aquaporin 4 (AQP4) IgG-seropositive NMOSD, myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD), and double-seronegative NMOSD. The past years have seen important advances in understanding rare demyelinating central nervous system (CNS) disorders associated with AQP4-IgG and MOG-IgG antibodies. Most of the recent literature has focused on the identification of clinical and magnetic resonance imaging (MRI) features that help distinguish these diseases from each other, simultaneously highlighting major diagnostic pitfalls that may lead to misdiagnosis. The present study aims to understand the epidemiology and disease characteristics of NMOSD and MOGAD in our population and compare them with previously published reports.Materials and methodsThis was a prospective, single-center, comparative, observational study conducted over 18 months. Thirty patients were recruited and categorized into two groups: NMOSD and MOGAD. Each group consisted of 15 patients. Data regarding neurological assessment, neuroimaging, treatment, and outcome were collected. These patients were followed at one, three, six, and 12 months for treatment response, residual disability, and relapse. Disease severity and disability were assessed by using the Expanded Disability Status Scale (EDSS) and modified Rankin scale (mRS).ResultsThe average age at presentation of the NMOSD group of patients was 34.67 ± 15.66 years, which was significantly higher compared to the 26 ± 5.74 years seen for the MOGAD group (p < 0.0001). The MOGAD group of patients had a significantly higher proportion of men compared to the NMOSD group (66.67% in MOGAD versus 0% in NMOSD). Optic neuritis was seen in a significantly higher proportion of MOGAD patients compared to the NMOSD group of patients (p = 0.0061). Bilateral optic neuritis was more common in the MOGAD group (26.67% vs. 6.67% in the NMOSD group). Isolated myelitis was higher in the NMOSD group. A higher proportion of patients in the NMOSD group received steroids along with rituximab (26.67%) compared to the MOGAD subgroup of patients. In terms of the rescue treatment, intravenous immunoglobulin (IVIG) or plasma exchange (PLEX) therapy was required more in the NMOSD group than the MOGAD group. The EDSS and mRS scores of both groups were comparable at baseline. However, on follow-up, the EDSS and mRS levels were significantly lower for the MOGAD group compared to the NMOSD group (p < 0.05). The overall relapse rate was 33.33% in the NMOSD group compared to 20% in the MOGAD group at 12 months.ConclusionNMOSD and MOGAD are two distinct CNS demyelinating disorders having different demographics, clinical profiles, treatment responses, relapse rates, and short-term outcomes. MOGAD patients appear to have younger age at onset, male predominance, less severe clinical presentation, good response to first-line treatment, fewer relapses, and better one-year functional outcomes whereas NMOSD has female predominance, more severe clinical attacks of myelitis and optic neuritis, less response to first-line management of acute attack requiring rescue therapy more often, less response to conventional immunosuppressive treatment with more relapses requiring escalation of maintenance therapy with rituximab, and significant visual and locomotor residual disability at 12 months.

Background:Myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD) is an acquired inflammatory demyelinating disease with optic neuritis (ON) as the most frequent clinical symptom. The hallmark of the disease is the presence of autoantibodies against MOG (MOG-IgG) in the serum of patients. Whereas the role of MOG in the experimental autoimmune encephalomyelitis animal model is well-established, the pathogenesis of the human disease and the role of human MOG-IgG is still not fully clear.Evidence Acquisition:PubMed was searched for the terms “MOGAD,” “optic neuritis,” “MOG antibodies,” and “experimental autoimmune encephalomyelitis” alone or in combination, to find articles of interest for this review. Only articles written in English language were included and reference lists were searched for further relevant papers.Results:B and T cells play a role in the pathogenesis of human MOGAD. The distribution of lesions and their development toward the optic pathway is influenced by the genetic background in animal models. Moreover, MOGAD-associated ON is frequently bilateral and often relapsing with generally favorable visual outcome. Activated T-cell subsets create an inflammatory environment and B cells are necessary to produce autoantibodies directed against the MOG protein. Here, pathologic mechanisms of MOG-IgG are discussed, and histopathologic findings are presented.Conclusions:MOGAD patients often present with ON and harbor antibodies against MOG. Furthermore, pathogenesis is most likely a synergy between encephalitogenic T and antibody producing B cells. However, to which extent MOG-IgG are pathogenic and the exact pathologic mechanism is still not well understood.

BackgroundMyelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) is a recently described autoimmune inflammatory disorder of the central nervous system (CNS). There is limited data on the association between Human Immunodeficiency virus (HIV) infection and MOGAD. We report three patients with HIV infection and myelin oligodendrocyte glycoprotein (MOG) antibodies in the setting of other central nervous system infections.Case descriptionsThe first patient, a 44-year-old black African man, presented with acute disseminated encephalomyelitis (ADEM) with positive serum MOG antibodies. He made a significant recovery with corticosteroids but had a quick relapse and died from sepsis. The second patient, an 18-year-old black woman, presented with paraplegia and imaging revealed a longitudinally extensive transverse myelitis and had positive serum MOG antibodies. She remained paraplegic after methylprednisone and plasmapheresis treatments. Her rehabilitation was complicated by development of pulmonary embolism and tuberculosis. The third patient, a 43-year-old mixed-race woman, presented with bilateral painless visual loss. Her investigations were notable for positive MOG antibodies, positive Varicella Zoster Virus on cerebral spinal fluid (CSF) and hyperintense optic nerves on magnetic resonance imaging (MRI). Her vision did not improve with immunosuppression and eventually died from sepsis.ConclusionOur cases illustrate the diagnostic and management challenges of MOGAD in the setting of advanced HIV infection, where the risk of CNS opportunistic infections is high even without the use of immunosuppression. The atypical clinical progression and the dilemmas in the diagnosis and treatment of these cases highlight gaps in the current knowledge of MOGAD among people with HIV that need further exploration.

Myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD) is the most recently defined inflammatory demyelinating disease of the central nervous system (CNS). Over the last decade, several studies have helped delineate the characteristic clinical-MRI phenotypes of the disease, allowing distinction from aquaporin-4 (AQP4)-IgG-positive neuromyelitis optica spectrum disorder (AQP4-IgG+NMOSD) and multiple sclerosis (MS). The clinical manifestations of MOGAD are heterogeneous, ranging from isolated optic neuritis or myelitis to multifocal CNS demyelination often in the form of acute disseminated encephalomyelitis (ADEM), or cortical encephalitis. A relapsing course is observed in approximately 50% of patients. Characteristic MRI features have been described that increase the diagnostic suspicion (e.g., perineural optic nerve enhancement, spinal cord H-sign, T2-lesion resolution over time) and help discriminate from MS and AQP4+NMOSD, despite some overlap. The detection of MOG-IgG in the serum (and sometimes CSF) confirms the diagnosis in patients with compatible clinical-MRI phenotypes, but false positive results are occasionally encountered, especially with indiscriminate testing of large unselected populations. The type of cell-based assay used to evaluate for MOG-IgG (fixed vs. live) and antibody end-titer (low vs. high) can influence the likelihood of MOGAD diagnosis. International consensus diagnostic criteria for MOGAD are currently being compiled and will assist in clinical diagnosis and be useful for enrolment in clinical trials. Although randomized controlled trials are lacking, MOGAD acute attacks appear to be very responsive to high dose steroids and plasma exchange may be considered in refractory cases. Attack-prevention treatments also lack class-I data and empiric maintenance treatment is generally reserved for relapsing cases or patients with severe residual disability after the presenting attack. A variety of empiric steroid-sparing immunosuppressants can be considered and may be efficacious based on retrospective or prospective observational studies but prospective randomized placebo-controlled trials are needed to better guide treatment. In summary, this article will review our rapidly evolving understanding of MOGAD diagnosis and management.

Background and Objective: Myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD) is a significant component of demyelinating diseases in pediatric populations. Recently, diagnostic criteria for MOGAD were established. This study aims to evaluate and compare the diagnostic efficacy of the fixed-cell-based assay (Fixed-CBA) and the live cell-based assay (Live-CBA) in patients who meet the 2023 clinical diagnostic criteria for MOGAD. Methods: This retrospective study included patients suspected of having MOGAD who were enrolled between June 2023 and June 2024. Patients were selected based on the “core clinical demyelinating events” outlined in the 2023 proposed criteria of the International MOGAD Panel. Patients with multiple sclerosis (MS), neuromyelitis optica spectrum disorders (NMOSD) with aquaporin-4 antibody-positive (AQP4-Abs-positive), and non-central nervous system (non-CNS) inflammatory diseases were chosen as controls. Serum samples were simultaneously tested for MOG-Abs using Fixed-CBA and Live-CBA. Results: A total of 86 patients were enrolled in the study: 52 in the suspected MOGAD group and 34 in the control group. Out of these patients studied, 16 presented with optic neuritis (ON), 5 with myelitis, 8 with acute disseminated encephalomyelitis (ADEM), and 7 with cortical encephalitis. Sixteen patients could not be classified by clinical phenotype. The highest MOG-Ab positivity rate was among patients with cortical encephalitis [85.7% (Live-CBA)/71.4% (Fixed-CBA)]. Both assays identified 22 positive samples, with Fixed-CBA and Live-CBA sensitivities at 44.2% and 55.8%, respectively, and a specificity of 97%. Of the patients suspected of having MOGAD, 19 cases were confirmed using the Fixed-CBA, while 28 cases were confirmed using the Live-CBA. This resulted in an upgrade in diagnostic classification for nine cases. This led to a diagnostic reclassification in nine cases. Conclusions: Both the Fixed-CBA and Live-CBA were associated with higher sensitivity for patients selected based on the 2023 MOGAD clinical diagnostic criteria. The Live-CBA exhibited an 11.6% increase in sensitivity, contributing to a 17.3% (9/52) enhancement in clinical diagnostic accuracy.

Myelin oligodendrocyte glycoprotein antibody-associated disease is an immune-mediated demyelinating disease of the central nervous system that is present in both adults and children. The most common clinical manifestations are optic neuritis, myelitis, acute disseminated encephalomyelitis, and brainstem syndrome. Cerebral cortical encephalitis (CCE) is a rare clinical phenotype of myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD), which usually begins with seizures, headaches, and fever, and may be misdiagnosed as viral encephalitis in the early stages. Herein, we report two typical MOG antibody (MOG-Ab)-positive patients presenting with CCE, both of whom presented with headache, fever, seizures, and who recovered completely after immunotherapy. In addition, we performed a systematic review of the present literature from the perspectives of population characteristics, clinical symptoms, MRI abnormalities, treatments, and prognosis. Among the patients reported in 25 articles, 33 met our inclusion criteria, with the age of onset ranging from 4 to 52 years. Most of the patients had seizures, headache, fever, and unilateral cortical lesions on brain MRI. For acute CCE, 30 patients were treated with high-dose intravenous methylprednisolone, and the symptoms of most patients were completely relieved after immunotherapy. This study reported our experience and lessons learned in the diagnosis and treatment of MOG-Ab-positive CCE and provides a systematic review of the literature to analyse this rare clinical phenotype.

Myelin oligodendrocyte glycoprotein (MOG-IgG) antibodies have been associated with a variety of demyelinating neurologic disorders, including optic neuritis. It remains unclear whether the presence of MOG-IgG represents a distinct syndrome or is simply a marker for central demyelination. Two experts, John J. Chen, MD, PhD, and Clare L. Fraser, MBBS, MMed, debate this topic. Pro: John J. Chen, MD, PhD Opening Statement In medicine, physicians and other providers often adopt the preference of being either a "lumper" or "splitter" when it comes to disease processes with overlapping characteristics. However, once a molecular basis is identified that reliably distinguishes one disease entity from another, particularly in a situation for which such a distinction affects treatment, being a "lumper" could lead to delays in our diagnosis, initiation of best therapies, and understanding of the disease process. The understanding of neuromyelitis optica spectrum disorder (NMOSD) is a perfect example of how serologic diagnosis has advanced characterization of demyelinating disease. Just over a decade ago, there was debate as to whether neuromyelitis optica (NMO) was a separate entity from multiple sclerosis (MS) (1). However, the discovery of antibodies to aquaporin-4 (AQP4-IgG) in 2004 cemented NMOSD as a separate disorder and revolutionized our understanding of the pathophysiology, clinical characteristics, and treatment of the disease (2,3). More recently, antibodies against myelin oligodendrocyte glycoprotein (MOG-IgG) have emerged as a reproducible marker for a subset of patients with optic neuritis and other demyelinating event phenotypes. While there is some clinical overlap with other demyelinating disorders, MOG-IgG–associated demyelinating disease is now becoming recognized as its own disease entity that is distinct from classic MS and AQP4-IgG–positive NMOSD (4,5). Characteristics suggestive of myelin oligodendrocyte glycoprotein disease The most common phenotype of MOG-IgG–positive demyelinating disease is optic neuritis, particularly when recurrent, followed by myelitis, acute disseminating encephalomyelitis (ADEM), and brainstem encephalitis (4–9). There are some characteristics of MOG-IgG–positive demyelinating disease that should alert the clinician to this possibility. Compared to other forms of acute demyelinating optic neuritis, MOG-IgG–positive optic neuritis has a higher likelihood of being recurrent, bilateral, and associated with prominent disc edema. Recurrent optic neuritis is seen in between 50% and 80% of cases of MOG-IgG–positive optic neuritis (6,7,9). This condition can sometimes be steroid responsive and dependent, thus meeting the criteria for what has previously been termed chronic relapsing inflammatory optic neuropathy (9–11). Bilateral simultaneous involvement occurs in almost 50% of cases of MOG-IgG–positive optic neuritis (6,7,9,12,13). Optic disc edema at onset is present in up to 86% (4,9,12–15). The disc edema can be severe, with peripapillary hemorrhages; these are a feature that is rarely seen in other forms of demyelinating optic neuritis. The vision loss is usually severe at the nadir, but recovery is typically better than that seen with AQP4-IgG–positive optic neuritis (7,9). On MRI, there is often longitudinally extensive enhancement of the optic nerve in those with MOG-IgG–positive optic neuritis (4,9,14,16,17). Perineural enhancement of the optic nerve sheath and peribulbar structures is seen in up to 50% of cases and is a fairly specific sign of this disorder, which is not typically seen with MS or AQP4-IgG–positive optic neuritis (9,15,16,18,19). Patients with longitudinally extensive transverse myelitis (≥3 contiguous vertebral segments) and negative AQP4-IgG antibody testing should be evaluated for MOG-IgG status; this is the case because such extensive spinal cord involvement is rarely seen in patients with classic MS. Transverse myelitis involves the conus medullaris in MOG-IgG disease more commonly than in other demyelinating diseases (including AQP4-IgG–positive transverse myelitis) (4,7,20). A recent study also found that the T2-signal abnormalities in the spinal cord are often restricted to the grey matter, forming a hallmark "H-sign" on axial images (20). An accompanying brainstem encephalitis and/or an ADEM-like presentation should also raise suspicion for MOG-IgG disease. These phenomena are less commonly seen in patients with AQP4-IgG–positive disease or in those with classic MS. Myelin oligodendrocyte glycoprotein–positive demyelinating disease is distinct from multiple sclerosis Although antibodies to myelin oligodendrocyte glycoprotein (MOG) were initially associated with MS based on nonspecific solid phase assay results (21), recent studies using transfected cell-based assays have found that MOG antibodies are almost never seen in patients with typical MS. In the process of optimizing the MOG-IgG assay at the Mayo Clinic, 50 patients with classic MS were tested, and none of them were positive for MOG-IgG (22). A follow-up study evaluating 86 patients with MOG-IgG–positive optic neuritis found only 1 patient with MS; this patient had a minimally elevated MOG-IgG binding index of 2.8 (laboratory cutoff of 2.5). In addition, none of the patients in that study had oligoclonal bands in the cerebral spinal fluid (CSF) (9). Many other groups have also found that patients with MOG-IgG–associated demyelinating disease do not have oligoclonal bands in the CSF and do not follow a classic MS disease course (5,7). Finally, a multicenter study of 200 patients and review of the literature found only 1 single borderline-positive MOG-IgG result among 290 patients with MS (23). The lack of coexisting MOG antibodies in patients with classic MS indicates that MOG-IgG disease is a distinct and separate process. Myelin oligodendrocyte glycoprotein–positive demyelinating disease is distinct from AQP4-IgG–positive neuromyelitis optica spectrum disorder Patients with antibodies to MOG can develop optic neuritis and longitudinally extensive transverse myelitis and thus fulfill the criteria for NMOSD, the disease process classically associated with AQP4-IgG. Approximately 30% of patients with NMOSD are seronegative for AQP4-IgG; recent studies have suggested that MOG-IgG is positive in approximately one-third of these patients (5,24,25). Much like MOG antibodies are rare in patients with MS, MOG-IgG is almost never seen in patients who have antibodies to AQP4 (26). This supports the concept that MOG-IgG disease and AQP4-IgG–positive NMOSD are separate entities (5). While there is clinical overlap between MOG-IgG–mediated and AQP4-IgG–mediated disease, the pathophysiologies are very different. Pathologic specimens from patients with AQP4-IgG–positive NMOSD show astrocyte destruction and secondary demyelination (27). In contrast, MOG-IgG–positive inflammatory disease tissue shows primary demyelination with preserved astrocytes; this was previously designated as Pattern II demyelination (5,26,28,29). Therefore, AQP4-IgG and MOG-IgG appear to be fundamentally distinct entities with different underlying pathophysiological bases. The importance of testing for myelin oligodendrocyte glycoprotein and recognizing myelin oligodendrocyte glycoprotein–positive demyelinating disease as a separate entity Testing for MOG antibodies, and recognizing MOG-IgG–positive demyelinating disease as a separate entity, truly matter because these distinctions influence our diagnostic ability, prognostication, and ultimately, our treatment of the patient. MOG-IgG disease can present with widespread central nervous system (CNS) inflammation that can be concerning for a vasculitic or infectious process. Much of what we know about the pathology for MOG-IgG disease was derived from brain biopsies performed because of diagnostic uncertainty; these were obtained before the advent of reliable cell-based assays for MOG-IgG. Now that we have a better understanding of the phenotype of MOG-IgG disease and have specific assays for MOG antibodies, diagnosing MOG-IgG disease with a simple serum test can lead to the correct diagnosis and exclude the necessity of a brain biopsy. As our understanding of MOG-IgG disease improves, formal diagnostic criteria will be developed and further refined in order to reliably diagnose this disorder. In addition, separating MOG-IgG disease from other demyelinating diseases will improve our understanding of the natural course. This will enhance our abilities to prognosticate and counsel our patients. Presumably because of the differences in pathogenesis, MOG-IgG–associated inflammation has better outcomes than AQP4-IgG disease even among patients who meet the current criteria for NMOSD. Despite a tendency to cause recurrent severe optic neuritis, the majority of patients with MOG-IgG–positive optic neuritis have meaningful recovery of vision and retain functional vision (7,9,30). This is unlike patients with AQP4-IgG–positive optic neuritis, for whom over one-third have poor visual outcomes (31–33). Recognizing MOG-IgG–demyelinating disease not only is helpful in diagnosis and prognosis but also may have a substantial impact on treatment. Recent studies have shown that MS disease-modifying agents are not effective in preventing relapses in the setting of MOG-IgG–associated disease (18,34,35). Treatment with MS disease-modifying agents could lead to the accumulation of CNS lesion burden from continued relapses; this could unwittingly lead to addition or escalation of what are actually ineffective disease-modifying agents, thus subjecting patients to unnecessary side effects. In addition, it is possible that MS disease-modifying agents could even worsen MOG-IgG–associated disease; this phenomenon has been seen in the setting of AQP4-IgG–positive NMOSD (4,5,18,36–38). The optimal treatments for AQP4-IgG and MOG-IgG diseases may be different as well. A recent multicenter study suggested that rituximab reduces relapse rates in MOG-IgG disease but not as effectively as it does for patients AQP4-IgG–positive NMOSD (39). Therefore, in the future, it will be important for patients with demyelinating disease to be classified according to their underlying molecular diagnosis rather than by a set of clinical criteria alone. Appreciating MOG-IgG–associated disease as its own entity will allow us to better understand the disease pathogenesis. This will be important because it will ultimately lead to directed therapies. Such a paradigm is being tested in ongoing clinical trials for AQP4-IgG–positive NMOSD. Lumping MOG-IgG–positive disease with other forms of demyelinating processes will hamper advancements that can be made for this unique entity. Con: Clare L. Fraser, MBBS, MMed, FRANZCO MOG is expressed exclusively in the CNS as a minor component of myelin. The protein structure of MOG is classified as an immunoglobulin and is found preferentially at the extracellular surface; MOG thus serves as a marker of oligodendrocyte maturation (40). MOG is also thought to serve in myelin adhesion, integrity, and cellular interactions (41). It is therefore studied as a target in CNS demyelinating disease. The potential role for MOG-IgG antibodies in AQP4-negative NMOSD was first suggested in 2007 (6). Following this, in vitro and patient cohort studies have pursued this link. Taking this line of thought one step further, it is suggested that MOG-IgG positivity may denote a disease entity in its own right. However, some of the studies have been limited by the assay type used, small patient numbers, limited diversity of the patients reviewed, and the lack of long-term follow-up data. Identification of MOG-IgG antibodies using cell-based assays (transfected or transduced with native human MOG in its conformational state and analyzed by flow cytometry or microscopy) have demonstrated the presence of this antibody in pediatric patients with ADEM or a relapsing demyelinating (MS-like) disease. Further studies using cell-based assays have shown MOG-IgG positivity in patients with NMOSD. Therefore, the data must be reviewed carefully before we decide if MOG antibody–associated optic neuritis is indeed a distinct entity. Consequence, not cause? To place MOG antibodies in the context of the current clinical literature, and thus this debate, it is important to review the animal studies. Experimental autoimmune encephalomyelitis (EAE) is an animal model of CNS demyelination. Induction of EAE requires immunizing the animal with CNS tissue homogenates or purified myelin components (42). This results in a complex immune response, including a strong T-cell–driven component. Transfer of encephalitogenic T cells can also initiate demyelination and EAE in animals. While MOG antibodies are part of this response, they alone do not necessarily result in the transfer of disease and are not required for severe clinical disease (40,43). This implies that immune system exposure to neurological tissue may result in MOG-IgG as a secondary consequence of preexisting damage; this is similar to the way in which antiretinal antibodies are found in conditions like retinitis pigmentosa. When the mouse IgG monoclonal antibody (mAb) equivalent of anti-MOG, known as 8-18C5 mAb, was transferred into animals that already had EAE, a hyperacute inflammatory response and extensive demyelinating plaques were seen. This suggests that perhaps MOG antibodies amplifies and modifies preexisting demyelinating pathology (44). Furthermore, this effect was dependent on the T cells having weakened the blood–brain barrier; there was no correlation between the antibody titers and the clinical disease (43). In mice, MOG-IgG only causes temporary damage of myelin and axons. More importantly, it does not produce inflammatory cell infiltration, axonal loss, neural degeneration, or astrocyte death (45). It could therefore be argued that perhaps MOG antibodies amplify preexisting disease rather than being a direct and separate pathological entity. The early published clinical research also points toward MOG antibodies being a broader consequence of neurological disease. In 1991, one group reported MOG-IgG in the CSF of 7 patients with MS, in 2 patients with "other inflammatory neurological disease" (OIND), and in 1 patient with tension headaches (46). Larger studies found MOG-IgG in 14%–33% of MS patients, 19%–55% of OIND, and in 3%–8% of noninflammatory neurological disease patients; this included all cases of neurosarcoid tested (47,48). MOG-IgG was also found in 10% of rheumatoid arthritis patients who had no neurological disease (47). Studies from this era are limited by the use of enzyme-linked immunosorbent assay (ELISA), which is less reliable than the newer assays. Even the newer cell-based assays are not without problems. In one study that used full-length human MOG, 48% of epilepsy control patients had a positive test result for MOG-IgG, which reduced to 5.8% when an IgG1-specific secondary antibody was used (49). These results would argue that MOG-IgG is a more generalized marker of inflammation, rather than a disease-causing antibody, in many forms of neurological disease. Chronic inflammatory CNS disease may induce autoantibodies by virtue of epitope spreading. In the MS literature, one study of 103 patients with clinically isolated syndrome found that 21% of patients were positive for both MOG-IgG and myelin basic protein IgM antibodies; 41% were positive for MOG antibodies alone. Those with antibodies to one or both myelin components were more likely to have relapses and to meet the criteria for clinically definite MS (21). The authors went on to emphasize that they could not prove whether the measured antibodies had demyelinating capacity or whether they represented an epiphenomenon of myelin destruction. Postmortem studies also showed higher levels of MOG antibodies within the MS lesions, compared to CSF and serum, suggesting local production as a consequence of disease (50). The authors also reported similar tissue findings in a patient with CNS aspergillosis. While most studies since this time have found MOG-IgG exclusively in patients with optic neuritis and/or myelitis who are AQP4-IgG negative, some concerns have been raised about the data (18). The cohorts included a median of 9 patients with only 24-month median follow-up; long-term follow-up was not available (6). Some cohorts contained no Caucasian patients or were genetically mixed. This may be of relevance as genetic (HLA-DRB-1 types) and infectious (Chlamydia pneumoniae, Helicobacter pylori) factors are thought to contribute to the pathogenesis of NMOSD (51). Finally, some control cohorts were too small to assess the specificity of the tests (6). Lumper or splitter? NMOSD is a demyelinating disorder of the CNS, typically presenting with optic neuritis or transverse myelitis (3). Since the discovery of AQP4 antibodies, it is now distinguishable from MS. However, 10%–25% of clinical NMOSD patients are negative for the AQP4 antibody. Therefore, assuming that MOG-IgG seropositivity does not per se constitute an "alternative diagnosis" from MS, then MOG-related conditions could still fit the 2015 diagnostic criteria for NMOSD (3). Jarius et al (18) found that 32% of patients with MOG-IgG met the 2015 NMOSD criteria, while 44% fulfilled the McDonald criteria for MS at the time of their study. However, AQP4-IgG–positive NMOSD is a disease of astrocytes, whereas MOG-IgG targets oligodendrocytes and therefore might be classified as a form of opticospinal MS (52). Perhaps, there are several routes to characterizing the final common pathways of the diseases we know as MS and NMOSD. Indeed, NMOSD may have 3 subtypes: AQP4-IgG–positive, MOG-IgG–positive, and dual positive cases. In a study of 174 patients, 2 cases tested positive to both MOG-IgG and AQP4-IgG antibodies (53). These 2 patients were women in their 50s who presented with bilateral simultaneous optic neuritis and longitudinally extensive transverse myelitis. Both patients tested positive for MOG-IgG and AQP4-IgG in both the serum and CSF. Mader et al (54) found that one-third of MOG-IgG–positive patients who fulfilled the diagnostic criteria for NMOSD also were AQP4-IgG positive. Dual serum positivity has also been reported in 1 patient with isolated optic neuritis in Japan and in 1 patient in China (55,56). In another study of recurrent optic neuritis (2 episodes separated by more than 1 month), 6 of 23 patients tested positive for both antibodies (57). Of these 6 patients, 50% failed to respond to high-dose corticosteroids and plasmapheresis, with visual acuity remaining poor. Using fluorescence-activated cell sorting, one group reported 10 patients (8%) with dual positivity to MOG-IgG and AQP4-IgG from a group of 125 patients with NMOSD (58). The majority of these patients have MS-like brain lesions on MRI, severe edematous multifocal changes on spine MRI, and pronounced loss of retinal nerve fiber layer thickness on optical coherence tomography, even in clinically unaffected eyes. The disease was typically multiphasic, with a high annual relapse rate and severe residual disability by Expanded Disability Status Scale and visual acuity testing. Yan et al (58) argue that a lack of similar findings in other studies was consequence of laboratory techniques that only allowed for the detection of antibodies in the extracellular or cell-surface domains. To date, I have not found any reports of double-positive antiacetylcholine receptor and muscle-specific kinase antibodies antibodies in myasthenia gravis, yet both forms of the disease are called myasthenia gravis! Why create 2 separate entities for AQP4 antibody and MOG antibody–positive demyelinating disease? Finally, the term MOG-IgG optic neuritis may be a misnomer because 80%–93% of such patients develop a relapsing disease; in addition, 52% develop more widespread neuroinflammatory changes, including myelitis, brainstem encephalitis and cerebellitis (6). Therefore, it seems more appropriate to say MOG-IgG–associated disease (new acronym—MAD?) spectrum disorder rather than MOG-IgG optic neuritis. Rebuttal: John J. Chen, MD, PhD Dr. Fraser has brought up several points that advance discussion of the importance of MOG antibodies in demyelinating disease. Dr. Fraser mentioned that prior studies on MOG-IgG were limited by small patient numbers. However, there are now many recent reports from large cohorts of patients spanning multiple ethnicities, with studies being published in Asia, Australia, the United Kingdom, France, the United States, Brazil, and many other countries (6,7,9,12,13,59,60). These larger studies have provided great insight into MOG-IgG–positive disease and have further shown that this is a distinct entity. I agree with Dr. Fraser that the early studies on MOG-IgG were fraught with difficulties and a lack of specificity; this incorrectly led to the notion that MOG-IgG was associated with MS. However, as Dr. Fraser mentioned, studies in this era were limited by the use of ELISA, which did not evaluate antibodies to MOG in its native form, leading to the poor specificity (61). The new cell-based assays use MOG in its native form which, in conjunction with optimization of the secondary antibodies, have led to very good to MOG are not found in patients, those with classic MS, patients with other optic or in those with other autoimmune disease While there are rare cases of simultaneous MOG and AQP4 antibody positivity in the these are rare with the use of the new cell-based assays and are limited to case In all of the large recent published on MOG-IgG, there have not been any cases of dual positivity for both MOG-IgG and AQP4-IgG While Dr. Fraser reported several of patients with MOG-IgG and these studies were and assays that were either not cell based or not with to the secondary There are likely rare cases of positivity because both MOG-IgG and AQP4-IgG demyelinating disease are autoimmune disorders, but this is an rather than the Therefore, autoantibodies to MOG are specific for a unique subset of patients with demyelinating disease and are not seen in other disease In addition, they are not an epiphenomenon of inflammatory CNS or optic nerve disease. It is still unclear whether MOG antibodies are or a marker of disease. A recent study demonstrated that MOG antibodies derived from with MOG-IgG disease were in demyelination on in 2 different EAE et al other potential that are distinct from AQP4-IgG–mediated disease. Even if antibodies to MOG up not being it is that MOG-IgG is a good marker of a specific disease process that is distinct from AQP4-IgG–mediated disease and from MS. This distinction has clinical and be because of the for prognosis and treatment. While some cases of MOG-IgG disease will meet the current criteria for NMOSD or the McDonald criteria for MS, these the lack of specificity in the diagnostic criteria rather than of MOG-IgG disease not being its own entity. There are unique to MOG-IgG disease that it from its MS and AQP4-IgG As MOG-IgG disease has a different presentation and MOG-IgG disease is seen in and unlike MS and AQP4-IgG disease that both have a The CSF for MOG-IgG–positive disease is distinct from that of MS As the pathology found on brain for MOG-IgG is different than what is found in AQP4-IgG disease. The best treatment for MOG-IgG has yet to be but it is that disease-modifying agents used to MS are not Therefore, MOG-IgG–positive disease has a different pathogenesis, and treatment. Lumping MOG-IgG into the disease process will hamper the understanding of this unique demyelinating process. to how distinct from MS over a decade with the discovery of the now that we have a specific and reliable marker for MOG-IgG disease, it will also its own separate disease. I agree with Dr. Fraser that MOG-IgG optic neuritis is not the most appropriate because MOG-IgG–positive disease can have a neuroinflammatory This has been called MOG-IgG encephalomyelitis according to a group of While the will likely its relevance as a distinct disease will Recognizing MOG-IgG disease as its own distinct entity will allow us to better understand the disease process and improve treatments for this disease. Rebuttal: Clare L. Fraser, MBBS, MMed, FRANZCO the the of is toward MOG-IgG optic neuritis being a distinct entity, which Dr. has I that we agree that it does more to a broader to the disease entity, such as MOG-IgG rather the condition to MOG-IgG optic neuritis this is particularly in Some of own in 1 were from the literature, with less for antibody testing than we now have In one of the early showed that patients with MOG antibody–associated demyelination to have a unique and the more clinical has led to and MOG-IgG–positive patients as having a separate disease process to MS and of MOG-IgG–associated demyelination was published The clinical response, and outcomes of patients were The that there remains diversity in associated with MOG-IgG–associated demyelination and that some overlap may be present between patients with clinically definite MS and MOG However, the literature on the clinical and phenotype and of treatment response, I agree with Dr. that this condition as a separate clinical entity from MS and NMOSD. In the that MOG-IgG antibody testing could be restricted to patients with a clinical and phenotype for MS, particularly in the event of isolated or recurrent optic neuritis While MOG-IgG–associated demyelination as an optic neuritis in the majority of patients, there is a clinical spectrum that to be broader than simply patients with NMOSD. the high of MOG-IgG positivity in it seems to test for MOG antibodies in all particularly if relapsing MD, and The to suggests that MOG-IgG–associated demyelinating disease may a distinct disorder with and that it from both MS and NMOSD. one is a or a the clinical spectrum of MOG is still It remains to be seen whether MOG antibodies are a marker for demyelination or whether these are per This may have for treatment and prognosis for MOG-IgG–associated demyelinating disease. Further studies and clinical the several will our understanding of this important