{'fraction_non_alphanumeric': 0.039558978336749956, 'fraction_numerical': 0.021663250041553547, 'mean_word_length': 4.73744437380801, 'pattern_counts': {'":': 0, '<': 2, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Myelin Oligodendrocyte Glycoprotein-Immunoglobulin G in the CSF

Background and Objective To investigate the clinical relevance of CSF myelin oligodendrocyte glycoprotein-immunoglobulin G (MOG-IgG) testing in a large multicenter cohort. Methods In this multicenter cohort study, paired serum-CSF samples from 474 patients with suspected inflammatory demyelinating disease (IDD) from 11 referral hospitals were included. After serum screening, patients were grouped into seropositive myelin oligodendrocyte glycoprotein antibody associated disease (MOGAD, 31), aquaporin-4-IgG-positive neuromyelitis optica spectrum disorder (AQP4-IgG + NMOSD, 60), other IDDs (217), multiple sclerosis (MS, 45), and non-IDDs (121). We then screened CSF for MOG-IgG and compared the clinical and serologic characteristics of patients uniquely positive for MOG-IgG in the CSF to seropositive patients with MOGAD. Results Nineteen patients with seropositive MOGAD (61.3%), 9 with other IDDs (CSF MOG + IDD, 4.1%), 4 with MS (8.9%), but none with AQP4-IgG + NMOSD nor with non-IDDs tested positive in the CSF for MOG-IgG. The clinical, pathologic, and prognostic features of patients uniquely positive for CSF MOG-IgG, with a non-MS phenotype, were comparable with those of seropositive MOGAD. Intrathecal MOG-IgG synthesis, observed from the onset of disease, was shown in 12 patients: 4 of 28 who were seropositive and 8 who were uniquely CSF positive, all of whom had involvement of either brain or spinal cord. Both CSF MOG-IgG titer and corrected CSF/serum MOG-IgG index, but not serum MOG-IgG titer, were associated with disability, CSF pleocytosis, and level of CSF proteins. Discussion CSF MOG-IgG is found in IDD other than MS and also in MS. In IDD other than MS, the CSF MOG-IgG positivity can support the diagnosis of MOGAD. The synthesis of MOG-IgG in the CNS of patients with MOGAD can be detected from the onset of the disease and is associated with the severity of the disease. Classification of Evidence This study provides Class II evidence that the presence of CSF MOG-IgG can improve the diagnosis of MOGAD in the absence of an MS phenotype, and intrathecal synthesis of MOG-IgG was associated with increased disability.


Discussion
CSF MOG-IgG is found in IDD other than MS and also in MS. In IDD other than MS, the CSF MOG-IgG positivity can support the diagnosis of MOGAD. The synthesis of MOG-IgG in the CNS of patients with MOGAD can be detected from the onset of the disease and is associated with the severity of the disease.

Classification of Evidence
This study provides Class II evidence that the presence of CSF MOG-IgG can improve the diagnosis of MOGAD in the absence of an MS phenotype, and intrathecal synthesis of MOG-IgG was associated with increased disability.
Myelin oligodendrocyte glycoprotein-immunoglobulin G (MOG-IgG) associated disease (MOGAD) has been regarded as a distinct disease of inflammatory demyelinating diseases (IDDs) involving CNS. 1,2 Serologic assays for MOG-IgG, using the full-length human MOG, has been widely accepted as an assay of choice to identify clinically relevant MOG-IgG in patient sera. 3,4 A recent cohort study identified 3 patients who only had MOG-IgG in their CSF 5 ; the clinical utility of CSF MOG-IgG detection is not clear. 6,7 Herein, we aimed to investigate the clinical utility of CSF testing for MOG-IgG in patients with suspected IDD and examine any clinical, pathologic, or prognostic implications of intrathecal MOG-IgG synthesis, using time-matched serum-CSF sample pairs.

Study Population and Data Collection
Paired serum and CSF from patients with suspected IDD were included from the prospectively collated database of 11 referral hospitals in Korea, from October 2011 to March 2020. Demographics, clinical, radiologic, and pathologic features of patients were obtained by case report form and medical record review. Disability at the time of sampling was measured by the Kurtzke Expanded Disability Status scale. 8 Serologic Assay for MOG-IgG and AQP4-IgG Assays for serum aquaporin-4 IgG (AQP4-IgG) were performed by an in-house flow cytometric assay using live cells expressing human M23 AQP4, as reported. 9,10 Assay for serum MOG-IgG were performed either by cell based assay at the John Radcliffe Hospital, Oxford, UK (103 samples, collected from October 2011 to November 2013), 3 or by inhouse flow cytometric assay (414 samples) with minor modifications of our previous methods 11,12 using full-length human MOG and anti-human IgG1 secondary antibody (Alexa Fluor 488 goat anti-human IgG1, 1:100 dilution; A10631, Invitrogen; Supplementary data 1, links.lww.com/NXI/A642).
CSF MOG-IgG Assay and Cutoff Value CSF draw and serum sampling were performed within 24 hours in 96.3% of the total CSF/serum pairs, and 99.2% were performed within 1 week. All CSF samples were stored at −80°C until required. The in-house flow cytometric assay for CSF MOG-IgG was performed in SNUH Neuroimmunology Laboratory using HEK -293 T cells transfected with the fulllength human MOG with a minor modification from our assay for serum MOG-IgG. 11,12 Briefly, cells were incubated with CSF (dilution 1:2 for 1 hour at 4°C), and anti-IgG Fc secondary antibodies (Alexa Fluor 488 goat antihuman IgG, 1:200 dilution, Jackson) were used. 5 The mean fluorescence intensity ratio (MFIr) of the patients' samples were determined using the following formula: MFIr = green MFI of patient's antibody binding to the dsRed-tagged MOG transfected cells (upper gate on red Glossary ADEM = acute disseminated encephalomyelitis; AQP4+ = aquaporin-4 antibody positive; AQP4-IgG + NMOSD = aquaporin-4 immunoglobulin G positive neuromyelitis optica spectrum disorder; CIS = clinically isolated syndrome; iATM = idiopathic acute transvers myelitis; IDD = inflammatory demyelinating disease; IgG = immunoglobulin G; MFIr = mean fluorescence intensity ratio; MOG = myelin oligodendrocyte glycoprotein; MOGAD = myelin oligodendrocyte glycoprotein antibody associated disease; MS = multiple sclerosis; OCB = oligoclonal band; RRMS = relapsing-remitting MS. channel)/green MFI of the same gate with healthy control sera ( Figure 1B).

Corrected CSF/Serum MOG-IgG Index
The MOG-IgG endpoint titers were obtained in any sample positive in the serum or CSF. Serum was titrated in doubling dilutions from 1:10 (range from 1:10 to 1:10,240), and CSF was titrated similarly from 1:2 (range from 1:2 to 1:512). The highest dilution with a positive result was considered the endpoint. To measure the same MOG-IgG isotypes in CSF and serum, the same secondary antibody against anti-IgG Fc (1: 200, Jackson) was used for both titrations (supplementary data 3, links.lww.com/NXI/A642). 3,20,21 The albumin quotient (Q alb = CSF/serum total albumin level), IgG quotient (Q IgG = CSF/serum total IgG level), and IgG index (Q IgG /Q alb ) were calculated. Using Q alb , the Q lim(IgG) was calculated as previous reported. Considering the possibility of blood-CSF barrier compromise, the corrected CSF/serum MOG-IgG index was calculated for the following 2 conditions, respectively. 22 The "intrathecal MOG-IgG synthesis" is defined as corrected CSF/serum MOG-IgG indices exceeding 4 or MOG-IgG detected uniquely in the CSF, using IgG Fc as the secondary antibody. 24

Data Availability
Individual participant data will not be made publicly available due to potential confidentiality concerns related to the rarity of the condition and the small study population. Further information about the datasets is available from the corresponding author upon reasonable request.

Participants
In total, 510 CSF/serum pairs from 474 patients with suspected IDD and complete clinical records were included. After serum screening for MOG-IgG and AQP4-IgG, and applying clinical criteria, our cohort included 31 seropositive   Table 1.
The brain and spinal MRI of the CSF MOG + IDD group revealed gray matter lesions involving basal ganglia and thalamus, large confluent lesions, unilateral cerebral cortical lesions, and brainstem lesions, all which have been proposed as typical MRI findings of MOGAD. 1,4,25,26 . No typical MS lesions such as ovoid lesions adjacent to the body of lateral ventricles or Dawson finger-like lesions were found in the CSF MOG + IDD group. One of our patients had severe cerebral atrophy as a sequelae of severe ADEMlike attacks, as was recently reported in patients with MOGAD ( Figure 2). 27  Relapsing (OCB) in CSF. A second patient (case 11) had brain MRI lesions involving periventricular white matter and brainstem, experienced a relapse, and has subsequently been relapse free for 2.8 years with glatiramer acetate, a disease modifying treatment for MS. The third patient (case 12) with RRMS was in the early stage of secondary progression at the time of CSF sampling, after 4 years of follow-up despite of interferon beta treatment. The CSF OCBs became positive at follow-up. The last patient with MS with low positive CSF MOG-IgG (case 13) had multiple ovoid lesions in the subcortical white matter and upper cervical spinal cord. She has been relapse free for 2.7 years with interferon beta. These clinical and radiologic findings of our patients with MS support the diagnosis of MS in these patients and suggest that CSF MOG-IgG assay can yield positive test results in some patients with MS ( Figure 3).

Intrathecal MOG-IgG Synthesis: When and for Whom?
We measured the MOG-IgG titer in both serum and CSF of 36 patients with MOG-IgG (18 seropositive only, 10 dual CSF and serum positive, and 8 CSF positive only) with sufficient volume and also calculated the corrected CSF/serum MOG-IgG index. All but 1 patient, a 14-year-old, were adults (aged ≥18). Twelve patients with MOGAD (4 dual positive and 8 CSF positive only) were considered to have intrathecal synthesis, either a corrected CSF/serum MOG-IgG index exceeding 4 in the dual positive individuals or MOG-IgG detected only in CSF. 24 Among these patients with intrathecal synthesis for MOG-IgG, 7 patients had their samples collected during the acute phase of the first attack (red dot in Figure 4A, mean 19 days after disease onset), which suggests that intrathecal synthesis of MOG-IgG can occur early in the disease course of MOGAD. Of note, both the presence of CSF-MOG IgG and intrathecal MOG-IgG synthesis were associated with the involvement of the brain or spinal cord ( Figure 4B and C). In our intrathecal MOG-IgG synthesis (+) group, all patients had brain/spinal cord involvement, and most manifested clinically as ADEM (7/12). In contrast, the intrathecal MOG-IgG synthesis (−) group predominantly presented as isolated optic neuritis (75%; p < 0.001). In addition to the difference in lesion location and clinical manifestations, the intrathecal MOG-IgG synthesis (+) group were younger and had higher number of white blood cells in the CSF (eTable 3, links.lww.com/NXI/A642).

MOG-IgG Titer in the CSF: Association With Disability and CSF Pleocytosis
The degree of disability, number of white blood cells, and level of protein in the CSF of patients with MOGAD were associated with the MOG-IgG titer in the CSF but not in the serum. Moreover, they were also associated with the corrected CSF/ Serum MOG-IgG index, representing the degree of intrathecal MOG-IgG synthesis ( Figure 5).

Longitudinal Data of CSF MOG-IgG
The CSF had been collected more than twice in 28 patients  samples of sera and CSF at relapses were all consistently positive for MOG-IgG during 28 months of follow-up (eFigure 2, links.lww.com/NXI/A642).

Independent Confirmation of the CSF MOG-IgG Assay Accuracy
In total, 79 CSF samples were retested at the Oxford Autoimmune Neurology Diagnostic Laboratory, Oxford, UK, for an independent confirmation of CSF MOG-IgG positivity. All CSF samples tested positive for MOG-IgG in Seoul were also positive in Oxford, and the test results of these 2 centers were identical in 77/79 (97.5%) samples. Two additional MOGAD CSF samples that tested positive in Oxford. There was very good correlation between the flow cytometry in Seoul and the CBA score in Oxford (r = 0.7043, p < 0.001; eFigure 1, links.lww.com/ NXI/A642).

Discussion
The presence of MOG-IgG, detected on a live test, in the sera of patients with IDD confer a diagnosis of MOGAD. 1,4,13 The clinical utility of CSF testing for MOG-IgG is unclear. A recent single center cohort study identified 3 patients with a MOGAD phenotype who had MOG-IgG only in their CSF. A second study identified 4 children with a diagnosis of MS with CSF unique MOG-IgG. 5, 6 We sought to investigate the clinical relevance of CSF MOG-IgG testing in 474 consecutive patients from 11 tertiary referral hospitals. In total, we identified 32 individuals with MOG-IgG in their CSF. Among these, 19 of 31 (61%) were seropositive patients with MOGAD and 13 of 262 (5%) were uniquely positive in the CSF: 5 of 8 (62.5%) ADEM, 1 of 24 CIS (4.2%), 1 of 123 (0.8%) iATM, 2 of 49 (4.1%) ON, and 4 of 45 (8.9%) patients with MS. All patients with AQP4-IgG + NMOSD or with non-IDDs were negative.
These data confirm recent reports suggesting both MOGAD and MS cases are positive for MOG-IgG in the CSF. Further work on CSF titres may be required to improve disease specificity in CSF testing as has been necessary for serum testing.
The non-MS, CSF-uniquely positive individuals (n = 9) added another 29% to the serum antibody positive MOGAD group (n = 31). They had comparable clinical, radiologic, pathologic, and prognostic features to those of the seropositive patients with MOGAD. These data suggest that CSF testing in patients with a clinical syndrome compatible with MOGAD will significantly improve the capture of patients with MOGAD, particularly in seronegative patients with ADEM. Of note, 67% (6/9) of these patients had a relapsing disease and 78% (7/9) were untreated. Immunosuppression was associated with a relapse-free followup (eTable 1, links.lww.com/NXI/A642). Immunotherapy 33 will likely be useful for patients without MS with CSF MOG-IgG, most of whom relapsed.
Although the CSF MOG-IgG assay improves the diagnostic yield for MOGAD, a unique CSF positive result should be interpreted in the clinical context as 4/45 (8.9%) patients with MS were positive. Individuals with MS are rarely seropositive, and when positive is most often borderline as these assays were set-up to rule out typical MS. A similar titration of CSF samples may be needed to improve CSF test specificity. Alternatively, a better understanding of the pathology associated with MOG-IgG may help our interpretation of the presence of these CSF unique MOG-IgG, particularly in MS patients where they are currently not thought to be clinically relevant.
Several studies have shown that patients with MS have intrathecal production of polyspecific antibodies against diverse CNS debris 34 or antigens, including MOG. 35 These were more evident in secondary progressive MS where ectopic meningeal lymphoid follicles have been identified. 36,37 In this study, 1 of 3 patients with secondary progressive MS and a patient with RRMS just before secondary progression were uniquely positive in the CSF. Of note, some of us recently reported the presence of a secondary progressive disease course as an unusual manifestation of seropositive MOGAD. 28 Until recently, there has been little evidence for intrathecal synthesis of MOG-IgG. 22,38 In our patients with MOGAD, 12 (4 seropositive and 8 CSF positive only) had intrathecal MOG-IgG synthesis. Intrathecal MOG-IgG synthesis was found in samples collected at the time of first attack in 7, which suggested that MOG-IgG synthesis in the CNS is present at disease onset. It can persist throughout the disease course. In addition, both the CSF MOG-IgG titer and corrected CSF/serum MOG-IgG index, but not the serum MOG-IgG titer, correlated with higher disability at the time of attack, more brain and spinal cord involvement, and a higher number of inflammatory cells in the CSF of MOGAD. Finally, in an additional 29% patients with MOGAD, MOG-IgG was only detectable in the CSF. These findings seem to challenge the current dogma that B cells producing CNS-targeting antibodies are produced peripherally and subsequently gain access to the CNS. Rather, we speculate that this finding could imply that the synthesis of MOG-IgG in the CNS can play a role in MOGAD, at least among patients with intrathecal synthesis of MOG-IgG. Nevertheless, further studies, including the experimental model for MOGAD, are required to elucidate the exact role of intrathecal synthesis of MOG-IgG in the pathogenesis of MOGAD.
In the MOGAD group, the CSF MOG-IgG assay yielded a positive result in 61% patients, similar to previous studies (62%-71%). 5,6,38 However, we were unable to detect CSF MOG-IgG in most patients with an iON. The one-way flow of CSF from the intracranial subarachnoid space (SAS) to the orbital SAS 39 may explain this lack of detection in patients who are sampled via lumbar puncture.
Of note, recent report has demonstrated that the prevalence of CSF MOG-IgG among pediatric encephalitis patients is approximately 1.2%. 6,40 In our study, 3 CSF MOG + IDD patients diagnosed with ADEM also had features of seizure/ encephalitis.
In conclusion, in the correct clinical context CSF testing for MOG-IgG can improve the capture of MOGAD patients. Intrathecal synthesis of MOG-IgG can be detected in MOGAD from the onset of the disease and is associated with more severe disability at attack, higher number of inflammatory cells in the CSF, and more brain and spinal cord involvement. Further work is required to understand the pathobiology associated with intrathecally produced MOG-IgG to help explain why it seems clinically relevant in non-MS encephalomyelitis and yet seems irrelevant in patients with clinically definite MS.  Study conception and design, drafting and revising of the manuscript, data acquisition and analysis, statistical analysis, critical reading of the manuscript, and read and approved the final manuscript