Aquaporin 4 (AQP4)-IgG-positive neuromyelitis optica spectrum disorder (AQP4-IgG+NMOSD) is an autoimmune astrocytopathic disease pathologically characterized by the massive destruction and regeneration of astrocytes with diverse types of tissue injury with or without complement deposition. However, it is unknown whether this diversity is derived from differences in pathological processes or temporal changes. Furthermore, unlike for the demyelinating lesions in multiple sclerosis, there has been no staging of astrocytopathy in AQP4-IgG+NMOSD based on astrocyte morphology. Therefore, we classified astrocytopathy of the disease by comparing the characteristic features, such as AQP4 loss, inflammatory cell infiltration, complement deposition and demyelination activity, with the clinical phase. We performed histopathological analyses in eight autopsied cases of AQP4-IgG+NMOSD. Cases comprised six females and two males, with a median age of 56.5 years (range, 46–71 years) and a median disease duration of 62.5 months (range, 0.6–252 months). Astrocytopathy in AQP4-IgG+NMOSD was classified into the following four stages defined by the astrocyte morphology and immunoreactivity for GFAP: (i) astrocyte lysis: extensive loss of astrocytes with fragmented and/or dust-like particles; (ii) progenitor recruitment: loss of astrocytes except small nucleated cells with GFAP-positive fibre-forming foot processes; (iii) protoplasmic gliosis: presence of star-shaped astrocytes with abundant GFAP-reactive cytoplasm; and (iv) fibrous gliosis: lesions composed of densely packed mature astrocytes. The astrocyte lysis and progenitor recruitment stages dominated in clinically acute cases (within 2 months after the last recurrence). Findings common to both stages were the loss of AQP4, a decreased number of oligodendrocytes, the selective loss of myelin-associated glycoprotein and active demyelination with phagocytic macrophages. The infiltration of polymorphonuclear cells and T cells (CD4-dominant) and the deposition of activated complement (C9neo), which reflects the membrane attack complex, a hallmark of acute NMOSD lesions, were selectively observed in the astrocyte lysis stage (98.4% in astrocyte lysis, 1.6% in progenitor recruitment, and 0% in protoplasmic gliosis and fibrous gliosis). Although most of the protoplasmic gliosis and fibrous gliosis lesions were accompanied by inactive demyelinated lesions with a low amount of inflammatory cell infiltration, the deposition of complement degradation product (C3d) was observed in all four stages, even in fibrous gliosis lesions, suggesting the past or chronic occurrence of complement activation, which is a useful finding to distinguish chronic lesions in NMOSD from those in multiple sclerosis. Our staging of astrocytopathy is expected to be useful for understanding the unique temporal pathology of AQP4-IgG+NMOSD.

The spectrum of myelin oligodendrocyte glycoprotein (MOG)-IgG-associated disease (MOGAD) includes optic neuritis (ON), myelitis (MY), acute disseminated encephalomyelitis (ADEM), brainstem encephalitis, cerebral cortical encephalitis (CE), and aquaporin-4-IgG (AQP4-IgG)-negative neuromyelitis optica spectrum disorder (NMOSD). In MOGAD, MOG-IgG are usually detected in sera (MOG-IgG_SERUM), but there have been some seronegative MOGAD cases with MOG-IgG in CSF (MOG-IgG_CSF) and its diagnostic implications remains unclear. In this cross-sectional study, we identified patients with paired serum and CSF sent from all over Japan for testing MOG-IgG. Two investigators blinded to MOG-IgG status classified them into suspected MOGAD (ADEM, CE, NMOSD, ON, MY and Others) or not based on the current recommendations. The MOG-IgG_SERUM and MOG-IgG_CSF titres were assessed with serial two-fold dilutions to determine endpoint titres [≥1:128 in serum and ≥1:1 (no dilution) in CSF were considered positive]. We analysed the relations between MOG-IgG_SERUM, MOG-IgG_CSF, and the phenotypes with multivariable regression. A total of 671 patients were tested (405 with suspected MOGAD, 99 with multiple sclerosis, 48 with AQP4-IgG-positive NMOSD, and 119 with other neurological diseases [OND]) before treatment. In suspected MOGAD, 133 patients (33%) tested MOG-IgG-positive in serum and/or CSF; 94 (23%) double-positive (ADEM 36, CE 15, MY 8, NMOSD 9, ON 15, and Others 11), 17 (4.2%) serum-restricted-positive (ADEM 2, CE 0, MY 3, NMOSD 3, ON 5, and Others 4), and 22 (5.4%) CSF-restricted-positive (ADEM 3, CE 4, MY 6, NMOSD 2, ON 0, and Others 7) cases. None of AQP4-IgG-positive NMOSD, multiple sclerosis, or OND cases tested positive for MOG-IgG_SERUM but two with multiple sclerosis were MOG-IgG_CSF-positive; the specificity of MOG-IgG_SERUM and MOG-IgG_CSF in suspected MOGAD were 100% (95%CI 99%–100%) and 99% (97%–100%), respectively. Unlike AQP4-IgG-positive NMOSD, the correlation between MOG-IgG_SERUM and MOG-IgG_CSF titres in MOGAD was weak. Multivariable regression analyses revealed MOG-IgG_SERUM were associated with ON and ADEM, whereas MOG-IgG_CSF were associated with ADEM and CE. The number needed to test (NNT) of MOG-IgG_CSF to diagnose one additional MOGAD case was 13.3 (14.3 for ADEM, 2 for CE, 19.5 for NMOSD, infinite for ON, 18.5 for MY, and 6.1 for Others). In the status of MOG-IgG_SERUM/CSF, most cases were double-positive, while including either serum-restricted (13%) or CSF-restricted (17%). These statuses were independently associated with clinical phenotypes, especially with ON in serum and CE in CSF, suggesting these pathophysiologic implications and the utility of preferential diagnostic testing. Further studies are warranted for the clinical and pathological significance of compartmentalized MOG-IgG.

Myelin oligodendrocyte glycoprotein (MOG) antibody-associated disorder (MOGAD) is a newly identified autoimmune demyelinating disorder that is often associated with acute disseminated encephalomyelitis and usually occurs postinfection or postvaccination. Here we report a case of MOGAD after mRNA severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination. A previously healthy 68-year-old woman presented to our department with gradually worsening numbness on the right side of her face, which began 14 days after her second dose of an mRNA-1273 vaccination. The patient's brain MRI revealed a right cerebellar peduncle lesion with gadolinium enhancement, a typical finding of MOGAD. A neurological examination revealed paresthesia on her right V2 and V3 areas. Other neurological examinations were unremarkable. Laboratory workups were positive for serum MOG-IgG as assessed by live cell-based assays and the presence of oligoclonal bands in the cerebrospinal fluid (CSF). The patient's serum test results for cytoplasmic-antineutrophil cytoplasmic antibodies, perinuclear-cytoplasmic-antineutrophil cytoplasmic antibodies, GQ1b-antibodies, and aquaporin-4 antibodies (AQP4-IgG) were all negative. Tests for soluble interleukin (IL)-2 receptors in the serum, IL-6 in the CSF and skin pricks, and angiotensin converting enzyme tests were all unremarkable. The patient was diagnosed with MOGAD after receiving an mRNA SARS-CoV-2 vaccination. After two courses of intravenous methylprednisolone treatment, the patient's symptoms improved and her cerebellar peduncle lesion shrunk slightly without gadolinium enhancement. To date, there have only been two cases of monophasic MOGAD following SARS-CoV-2 vaccination, including both the ChAdOx1 nCOV-19 and mRNA-1273 vaccines, and the prognosis is generally similar to other typical MOGAD cases. Although the appearance of MOG antibodies is relatively rare in post-COVID-19–vaccine demyelinating diseases, MOGAD should be considered in patients with central nervous system (CNS) demyelinating diseases after receiving a SARS-CoV-2 vaccine.

In adult patients with MOG-Ab-associated disease (MOGAD), the highest occurrence of lesions was in the thalamus and pons in MOGADOR study,1 but the other study showed that MOGAD lesion was more often found in subcortical white matter and the internal capsule, but the pontine lesion was not revealed as distinct.2 In paediatric patients, the cerebellar peduncle was dominant in MOGAD, but there were no statistically significant differences in the pons, thalamus and cortical lesions.3 Such discrepancies might suggest a wide diversity in lesion configuration and extraction, range of diseases and various age of disease onsets.

To clarify T-cell responses in myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD), we cultured the peripheral blood mononuclear cells of 24 patients with MOGAD and 20 with aquaporin-4 (AQP4) antibody-positive neuromyelitis optica spectrum disorders (NMOSD), and those of 17 healthy controls (HCs), in the presence of fourteen MOG peptides covering the full-length MOG, five AQP4 peptides, two myelin basic protein peptides, or two proteolipid protein peptides. Then, we measured T-cell activation markers, such as cell surface CD69 and the intracellular production of granulocyte–macrophage colony-stimulating factor (GM-CSF) and interferon-γ in CD4-positive T-cells, with a flow cytometer. The expression of CD69 in response to MOG p16–40 and MOG p181–205 was significantly higher (Stimulation Index > 2) in MOGAD than in HCs. Also, CD69 for AQP4 p21–40, AQP4 p211–230, and MOG p166–190 were significantly increased in NMOSD than in HCs. Intracellular GM-CSF production responding to MOG p16–40 was significantly higher in MOGAD than in HCs (p < 0.05), although intracellular interferon-γ was not elevated. None of the responses to the other peptides were different between the groups. The present study showed subtle CD4-positive T-cell activation elicited by some MOG peptides alone in patients with MOGAD. Further studies of cytokines or other stimulation and alternative assay markers and metrics are needed to delineate the immunopathological roles of T-cells in MOGAD.