The clinical spectrum and immunobiology of parainfectious neuromyelitis optica (Devic) syndromes

Acute demyelinating encephalomyelitis in a child with pulmonary tuberculosis

Tuberculosis is a leading cause of mortality in children worldwide. One of the greatest challenges in its management is the difficulty of diagnosis as the manifestations are non-specific and often mimic other illnesses. Neurological infection occurs in approximately 1% of patients diagnosed with tuberculosis, and usually takes the form of tuberculous meningitis or tuberculoma. An 11-year-old girl who was diagnosed with acute disseminated encephalomyelitis, a rare immunological manifestation of tuberculosis, is presented. She recovered completely after a course of high-dose systemic corticosteroids in addition to anti-tuberculosis treatment. Considering the immense burden of this infectious disease, recognition and understanding of the uncommon manifestations are important to enable appropriate and timely treatment.Abbreviations: ADEM: acute disseminated encephalomyelitis; ATT: anti-tuberculosis therapy; CBNAAT: cartridge-based nucleic acid amplification test; CNS: central nervous system; CSF: cerebrospinal fluid; CT: computed tomography; FLAIR: fluid attenuated inversion recovery; IFN: interferon; MRI: magnetic resonance imaging; MTB: Mycobacterium tuberculosis; TB: tuberculosis; TNF: tumour necrosis factor.

Relapses and Serious Infections in Patients with Neuromyelitis Optica Spectrum Disorder Treated with Rituximab: A Swedish Single-Center Study

Neuromyelitis optica spectrum disorder (NMOSD) is a rare immune-mediated relapsing-remitting disease of the central nervous system. The usage of rituximab, as relapse-preventive therapy, in NMOSD is common. We performed a single-center retrospective cohort study to assess the risk of relapses and severe infectious events (SIEs) in rituximab-treated NMOSD patients. This study included 24 aquaporin-4 IgG+ (AQP4+), 8 myelin-oligodendrocyte-protein IgG+ (MOG+), and 10 double-seronegative NMOSD patients. Relapses were observed in 50% of all patients during a mean treatment time of 4.0 (range: 0.5-8.25) years. The incidence risk ratio (IRR) of relapse was three times higher in MOG+ compared to AQP4+ patients (IRR: 3.0, 95% confidence interval (CI); 1.2-7.7). SIEs occurred in 40% of all patients during follow-up. AQP4+ patients conferred an increased risk of SIEs compared to MOG+ patients (IRR; 5.3, 95% CI; 1.2-24.3). Incomplete CD19+ B-lymphocyte suppression was not correlated with relapse risk (hazard ratio; 1.9, 95% CI; 0.7-5.2), and there was no correlation between IgG-levels and SIE risk (odds ratio; 2.0, 95% CI; 0.8-4.8). In conclusion, considerable risks of both relapses and SIEs were observed in NMOSD patients exposed to rituximab, which underlines the need for close clinical vigilance of disease activity and infections during treatment.

Causal relationships between susceptibility and severity of COVID-19 and neuromyelitis optica spectrum disorder (NMOSD) in European population: a bidirectional Mendelian randomized study

Background

Neurological disorders can be caused by viral infections. The association between viral infections and neuromyelitis optica spectrum disorder (NMOSD) has been well-documented for a long time, and this connection has recently come to attention with the occurrence of SARS-CoV-2 infection. However, the precise nature of the causal connection between NMOSD and COVID-19 infection remains uncertain.

Methods

To investigate the causal relationship between COVID-19 and NMOSD, we utilized a two-sample Mendelian randomization (MR) approach. This analysis was based on the most extensive and recent genome-wide association study (GWAS) that included SARS-CoV-2 infection data (122616 cases and 2475240 controls), hospitalized COVID-19 data (32519 cases and 2062805 controls), and data on severe respiratory confirmed COVID-19 cases (13769 cases and 1072442 controls). Additionally, we incorporated a GWAS meta-analysis comprising 132 cases of AQP4-IgG-seropositive NMOSD (NMO-IgG+), 83 cases of AQP4-IgG-seronegative NMOSD (NMO-IgG-), and 1244 controls.

Results

The findings of our study indicate that the risk of developing NMO-IgG+ is elevated when there is a genetic predisposition to SARS-CoV-2 infection (OR = 5.512, 95% CI = 1.403-21.657, P = 0.014). Furthermore, patients with genetically predicted NMOSD did not exhibit any heightened susceptibility to SARS-CoV2 infection, COVID-19 hospitalization, or severity.

Conclusion

our study using Mendelian randomization (MR) revealed, for the first time, that the presence of genetically predicted SARS-CoV2 infection was identified as a contributing factor for NMO-IgG+ relapses.

Causal associations between prodromal infection and neuromyelitis optica spectrum disorder: A Mendelian randomization study

BACKGROUND AND PURPOSE

Prodromal infections are associated with neuromyelitis optica spectrum disorder (NMOSD), but it remains unclear which type of infection has a causal association with NMOSD. We aimed to explore the causal associations between four herpesvirus infections (chickenpox, cold sores, mononucleosis and shingles) and NMOSD, as well as between other types of infections and NMOSD.

METHODS

For data on infections, we used the genome-wide association study (GWAS) summary statistics from the 23andMe cohort. For outcomes, we used the GWAS data of participants of European ancestry, including 215 NMOSD patients (132 anti-aquaporin-4 antibody [AQP4-ab]-positive patients and 83 AQP4-ab-negative patients) and 1244 normal controls. Single-nucleotide polymorphism (SNP) identification and two-sample Mendelian randomization (MR) analyses were then performed.

RESULTS

In the 23andMe cohort, we identified one SNP for chickenpox (rs9266089 in HLA-B gene), one SNP for cold scores (rs885950 in the POU5F1 gene), one SNP for mononucleosis (rs2596465 in the HCP5 gene), and three SNPs for shingles (rs2523591 in the HLA-B gene; rs7047299 in the IFNA21 gene; rs9260809 in the MICD gene). The association between cold sores and AQP4-ab-positive NMOSD reached statistical significance (odds ratio [OR] 745.318; 95% confidence interval [CI] 22.176, 25,049.53 [p < 0.001, Q < 0.001]). The association between shingles and AQP4-ab-positive NMOSD was also statistically significant (OR 21.073; 95% CI 4.271, 103.974 [p < 0.001, Q < 0.001]). No significant association was observed between other infections and AQP4-ab-positive or AQP4-ab-negative NMOSD.

CONCLUSION

These findings suggest there are positive associations between cold sores and shingles and AQP4-ab-positive NMOSD, indicating there may be causal links between herpes simplex virus and varicella-zoster virus infection and AQP4-ab-positive NMOSD.

[A case of neuromyelitis optica spectrum disorder after human immunodeficiency virus infection treated with rituximab]

The patient was a 58-year-old Japanese man. At age 52 years, he was diagnosed with human immunodeficiency virus (HIV) infection and had been receiving highly active antiretroviral therapy (HAART). He presented to the emergency department with acute upper left and right lower extremity paralysis. Spinal cord magnetic resonance imaging showed intramedullary signal changes over three vertebral bodies in the cervical spinal cord. Anti-aquaporin-4 antibody was positive in serum, and neuromyelitis optica spectrum disorder (NMOSD) was diagnosed. Steroid pulse therapy and plasma exchange were performed but had limited effects. In Japan, there is no report of NMOSD after HIV infection treated with rituximab. Rituximab administration should be considered in refractory cases of NMOSD after HIV infection.

Recurrent Regional Autonomic Dysfunction as a Presentation of Relapsing Neuromyelitis Optica Spectrum Disorder, Responsive to Ketamine Infusion

Diagnostic criteria of neuromyelitis optica spectrum disorders (NMOSD) have expanded to include many new symptoms since the original description of Devic's disease in 1894, and the formulation of diagnostic criteria in 2006. Herein, we describe a patient with serum aquaporin positive NMOSD with the unusual presentation of recurrent regional autonomic dysfunction, with concordant MRI findings. The symptomatic treatment of the patient's causalgia required IV ketamine infusion. Besides, as the long segment myelitis occurred in the setting of extensively drug-resistant tuberculosis (XDR TB), there was the added challenge of ruling out TB myelitis and choosing an immunosuppressant that would have the least risk of reactivation of TB.

New onset or relapsing neuromyelitis optica temporally associated with SARS-CoV-2 infection and COVID-19 vaccination: a systematic review

Background

Neuromyelitis optica spectrum disorder (NMOSD) is a rare chronic neuroinflammatory autoimmune condition. Since the onset of the COVID-19 pandemic, there have been reports of NMOSD clinical manifestations following both SARS-CoV-2 infections and COVID-19 vaccinations.

Objective

This study aims to systematically review the published literature of NMOSD clinical manifestations associated with SARS-CoV-2 infections and COVID-19 vaccinations.

Methods

A Boolean search of the medical literature was conducted between December 1, 2019 to September 1, 2022, utilizing Medline, Cochrane Library, Embase, Trip Database, Clinicaltrials.gov, Scopus, and Web of Science databases. Articles were collated and managed on Covidence^® software. The authors independently appraised the articles for meeting study criteria and followed PRISMA guidelines. The literature search included all case reports and case series that met study criteria and involved NMOSD following either the SARS-CoV-2 infection or the COVID-19 vaccination.

Results

A total of 702 articles were imported for screening. After removing 352 duplicates and 313 articles based on exclusion criteria, 34 articles were analyzed. A total of 41 cases were selected, including 15 patients that developed new onset NMOSD following a SARS-CoV-2 infection, 21 patients that developed de novo NMOSD following COVID-19 vaccination, 3 patients with known NMOSD that experienced a relapse following vaccination, and 2 patients with presumed Multiple Sclerosis (MS) that was unmasked as NMOSD post-vaccination. There was a female preponderance of 76% among all NMOSD cases. The median time interval between the initial SARS-CoV-2 infection symptoms and NMOSD symptom onset was 14  days (range 3-120  days) and the median interval between COVID-19 vaccination and onset of NMO symptoms was 10  days (range 1 to 97  days). Transverse myelitis was the most common neurological manifestation in all patient groups (27/41). Management encompassed acute treatments such as high dose intravenous methylprednisolone, plasmapheresis, and intravenous immunoglobulin (IVIG) and maintenance immunotherapies. The majority of patients experienced a favorable outcome with complete or partial recovery, but 3 patients died.

Conclusion

This systematic review suggests that there is an association between NMOSD and SARS-CoV-2 infections and COVID-19 vaccinations. This association requires further study using quantitative epidemiological assessments in a large population to better quantify the risk.

Secondary immunoreaction in patients with neurosyphilis and its relevance to clinical outcomes

Background and purpose

Several reported cases of autoimmune conditions such as anti-NMDAR encephalitis and neuromyelitis optica (AQP4) have been considered to be potentially secondary to Treponema pallidum infection. Since the role of immune impairment in neurosyphilis is unclear, in this retrospective study, we examined the correlation of the immune impairment in patients with neurosyphilis with their clinical characteristics and outcomes.

Methods

Clinical information was collected from patients with neurosyphilis in our center from January 2019 to December 2021. Cerebrospinal fluid (CSF) samples were subjected to indirect immunofluorescence tissue-based assay (IIF-TBA) on mouse brain sections and cell-based assay (CBA). The clinical characteristics and treatment outcomes of TBA-positive and-negative patients were compared.

Results

A total number of 81 patients diagnosed with neurosyphilis were included. The results of the CBA tests showed that three cases had anti-NMDAR, AQP4, or GAD65 antibodies, respectively. By TBA test, 38 patients (38/81, 46.9%) had positive immunostains, including staining of neuronal cells in 21 cases (21/38, 55.3%), glial cells in 11 cases (11/38, 28.9%), and neuronal and glial cells in six cases (6/38, 15.8%). We then compared the clinical characteristics and treatment outcomes between the TBA-positive and-negative patients and found that TBA-positive staining was significantly correlated with syphilis antibody titers (p = 0.027 for serum and p = 0.006 for CSF) and head MRI abnormalities (p < 0.001 for parenchymal abnormalities and p = 0.013 for white matter lesions). The cognitive prognosis of TBA-positive neurosyphilis patients was significantly worse than that of TBA-negative patients (p < 0.001).

Conclusion

The correlation between the TBA results and clinical data of our neurosyphilis patients imply the presence of secondary immune damage, which affected their prognosis. Therefore, TBA can be used as an additional biomarker for neurosyphilis patient prognosis.

The Role of Microorganisms in the Etiopathogenesis of Demyelinating Diseases

Multiple sclerosis (MS), neuromyelitis optica (NMO) and myelin oligodendrocyte glycoprotein antibody disease (MOGAD) are inflammatory diseases of the central nervous system (CNS) with a multifactorial aetiology. Environmental factors are important for their development and microorganisms could play a determining role. They can directly damage the CNS, but their interaction with the immune system is even more important. The possible mechanisms involved include molecular mimicry, epitope spreading, bystander activation and the dual cell receptor theory. The role of Epstein-Barr virus (EBV) in MS has been definitely established, since being seropositive is a necessary condition for the onset of MS. EBV interacts with genetic and environmental factors, such as low levels of vitamin D and human endogenous retrovirus (HERV), another microorganism implicated in the disease. Many cases of onset or exacerbation of neuromyelitis optica spectrum disorder (NMOSD) have been described after infection with Mycobacterium tuberculosis, EBV and human immunodeficiency virus; however, no definite association with a virus has been found. A possible role has been suggested for Helicobacter pylori, in particular in individuals with aquaporin 4 antibodies. The onset of MOGAD could occur after an infection, mainly in the monophasic course of the disease. A role for the HERV in MOGAD has been hypothesized. In this review, we examined the current understanding of the involvement of infectious factors in MS, NMO and MOGAD. Our objective was to elucidate the roles of each microorganism in initiating the diseases and influencing their clinical progression. We aimed to discuss both the infectious factors that have a well-established role and those that have yielded conflicting results across various studies.

Transverse myelitis following COVID-19: Insights from a multi-center study and systematic literature review

INTRODUCTION

We aimed to provide insights into transverse myelitis (TM) following COVID-19 by analyzing cases treated at tertiary care neurology centers and a systemic review of the literature.

METHODS

The retrospective observational multi-center study was conducted at the four university neurology departments in Croatia, Slovenia, Serbia, and Austria. We searched for acute myelitis cases that occurred during or after COVID-19. A systemic review of the literature on COVID-19 and transverse myelitis was performed.

RESULTS

We identified 76 persons with TM associated with COVID-19, 13 from the multi-center study and 63 from the literature review. Most of the participants (55.6%) had an intermediate latency, 25.4% had short and 19% long latency from COVID-19 symptoms to TM. The clinical presentation consisted of the typical TM signs. More than half of the participants had inflammatory changes in the CSF, with rare patients having intrathecal OCB synthesis and positive serology for anti-MOG or anti-AQP4 antibodies. Persons with autonomic symptoms and CSF pleocytosis were significantly more common to have an intermediate latency of 8 to 21 days from COVID-19 to TM (p = 0.005 and p = 0.003; respectively). According to logistic regression analysis, only participants with lesions evident on spinal cord MRI compared to normal spinal cord MRI had reduced risks for poor recovery. >80% of participants were treated with a combination of corticosteroids and intravenous immunoglobulins or plasma exchange with 73% having incomplete recovery.

CONCLUSION

Our study further characterizes clinical, laboratory, and MRI features, as well as treatment of TM associated with COVID-19.

Central nervous system (CNS) inflammatory demyelinating diseases (IDDs) associated with COVID-19: A case series and review

BACKGROUND

Over the past two years, SARS-CoV-2 has frequently been documented with various post and para-infectious complications, including cerebrovascular, neuromuscular, and some demyelinating conditions such as acute disseminated encephalomyelitis (ADEM). We report two rare neurological manifestations post-COVID-19 infection; multiple sclerosis (MS) and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD). Further, we reviewed other CNS inflammatory demyelinating diseases (IDDs) associated with SARS-CoV-2, including optic neuritis (ON) and neuromyelitis optica spectrum disorders (NMOSD).

METHODS

A descriptive analysis and literature search of Google Scholar and PubMed was conducted by two independent reviewers from December 1st, 2019, to March 30th, 2022, and included all the case studies of MS, MOGAD, NMOSD, and ON associated with COVID-19 infection.

CASE PRESENTATIONS

Case 1 (MS) was a 24-year-old female with paresthesia and bilateral weakness one week after COVID-19 symptom onset who showed demyelinating plaques and 12 isolated oligoclonal bands (OCBs). Case 2 (MOGAD) was a 41-year-old male with encephalomyelitis 16 days after COVID-19, who later developed MOG-antibody-associated optic neuritis.

RESULTS

Out of 18 cases, NMOSD was the most common post-COVID manifestation (7, 39%), followed by MOGAD (5, 28%), MS (4, 22%), and isolated ON (2, 11%). The median duration between the onset of COVID-19 symptom onset and neurological symptoms was 14 days. 61% of these were male, with a mean age of 35 years. IVMP was the treatment of choice, and nearly all patients made a full recovery, with zero fatalities.

CONCLUSIONS

Although these neurological sequelae are few, physicians must be cognizant of their underlying pathophysiology and associated clinical and neuro-diagnostic findings when treating COVID-19 patients with atypical presentations.

Association between infections, the microbiome, vaccination, and neuromyelitis optica spectrum disorder

Neuromyelitis optica spectrum disorder (NMOSD) is a devastating antibody-mediated condition of the central nervous system. As in other autoimmune diseases, there is considerable evidence to suggest that NMOSD arises from complex interactions between genetic susceptibility and environmental factors. However, whether factors like aquaporin-4-Antibody production initiate NMOSD attacks, currently remains unclear, and requires further investigation. Infectious diseases have also been proposed as possible environmental factors associated with NMOSD onset or relapses, some of which are more common in Asia and Latin America than in Europe and North America, in parallel with the higher incidence of NMOSD in these geographic locations. In this review, we examine current evidence on specific infections and vaccines associated with NMOSD onset and/or attacks, as well as the most recent data on gut microbiome composition and SARS-CoV-2 infection in NMOSD patients.

GANAB and N-Glycans Substrates Are Relevant in Human Physiology, Polycystic Pathology and Multiple Sclerosis: A Review

Glycans are one of the four fundamental macromolecular components of living matter, and they are highly regulated in the cell. Their functions are metabolic, structural and modulatory. In particular, ER resident N-glycans participate with the Glc3Man9GlcNAc2 highly conserved sequence, in protein folding process, where the physiological balance between glycosylation/deglycosylation on the innermost glucose residue takes place, according GANAB/UGGT concentration ratio. However, under abnormal conditions, the cell adapts to the glucose availability by adopting an aerobic or anaerobic regimen of glycolysis, or to external stimuli through internal or external recognition patterns, so it responds to pathogenic noxa with unfolded protein response (UPR). UPR can affect Multiple Sclerosis (MS) and several neurological and metabolic diseases via the BiP stress sensor, resulting in ATF6, PERK and IRE1 activation. Furthermore, the abnormal GANAB expression has been observed in MS, systemic lupus erythematous, male germinal epithelium and predisposed highly replicating cells of the kidney tubules and bile ducts. The latter is the case of Polycystic Liver Disease (PCLD) and Polycystic Kidney Disease (PCKD), where genetically induced GANAB loss affects polycystin-1 (PC1) and polycystin-2 (PC2), resulting in altered protein quality control and cyst formation phenomenon. Our topics resume the role of glycans in cell physiology, highlighting the N-glycans one, as a substrate of GANAB, which is an emerging key molecule in MS and other human pathologies.

Can Immune Tolerance Be Re-established in Neuromyelitis Optica?

Neuromyelitis optica (NMO) is a chronic inflammatory disease of the central nervous system that primarily affects the optic nerves and spinal cord of patients, and in some instances their brainstem, diencephalon or cerebrum as spectrum disorders (NMOSD). Clinical and basic science knowledge of NMO has dramatically increased over the last two decades and it has changed the perception of the disease as being inevitably disabling or fatal. Nonetheless, there is still no cure for NMO and all the disease-modifying therapies (DMTs) are only partially effective. Furthermore, DMTs are not disease- or antigen-specific and alter all immune responses including those protective against infections and cancer and are often associated with significant adverse reactions. In this review, we discuss the pathogenic mechanisms of NMO as they pertain to its DMTs and immune tolerance. We also examine novel research therapeutic strategies focused on induction of antigen-specific immune tolerance by administrating tolerogenic immune-modifying nanoparticles (TIMP). Development and implementation of immune tolerance-based therapies in NMO is likely to be an important step toward improving the treatment outcomes of the disease. The antigen-specificity of these therapies will likely ameliorate the disease safely and effectively, and will also eliminate the clinical challenges associated with chronic immunosuppressive therapies.

Non-infectious mechanisms of neurological damage due to infection

Infections of the nervous system is a growing aspect of clinical neurology. Accumulating knowledge in early diagnosis, course, therapy and prognosis is enlarging the clinical tools required for effective therapy. Of special importance is the ability to differentiate between proper infections, where anti-microbial agents, when available, should be introduced and used and post infectious conditions where therapy is mainly directed against the host immune system. The two conditions sometimes overlap, a situation that requires the ability to combine clinical skills with the use of laboratory tools such as polymerase chain reaction (PCR), serology, and antigenic detection. In the era of the SARS-CoV-2 pandemic, the need to make this distinction is emphasized as correct diagnosis of post infectious conditions and expedited therapy is important and sometimes lifesaving. We here attempt to present several infectious agents and their possible indirect damage to the nervous system causing in some cases significant neurological deficits. We try to limit our focus on those mechanisms which do not involve the direct tissue damage by the infectious agents but rather are connected to para- and post-infectious mechanisms. We attempt to delineate the features that will enable to tailor the correct diagnosis and following the effective therapy.

Uncommon inflammatory/immune-related myelopathies

The differential diagnosis for immune-mediated myelopathies is broad. Although clinical manifestations overlap, certain presentations are suggestive of a particular myelopathy etiology. Spine MRI lesion characteristics including the length and location, and the pattern of gadolinium enhancement, help narrow the differential diagnosis and exclude an extrinsic compressive cause. The discovery of specific antibodies that serve as biomarkers of myelitis such as aquaporin-4-IgG and myelin-oligodendrocyte -glycoprotein-IgG (MOG-IgG), has improved our understanding of myelitis pathophysiology and facilitated diagnosis. In this review we will focus on the pathophysiology, clinical presentation, imaging findings and treatment and outcomes of uncommon immune-mediated myelopathies.

Are Zika virus cross-reactive antibodies against aquaporin-4 associated to Neuromyelitis Optica Spectrum Disorder?

Zika virus (ZIKV) infection has been associated with the development of Neuromyelitis Optica Spectrum Disorder (NMOSD). ZIKV-induced antibodies that putatively cross-react to aquaporin-4 (AQP4) protein are suggested to cause inflammation of the optic nerve. A region of similarity between AQP4 and the ZIKV NS2B protein was identified. Our data showed that ZIKV-associated NMOSD patients develop anti-AQP4 antibodies, but not anti-ZIKV NS2B antibodies, revealing that cross-reacting antibodies are not the underlying cause of this phenotype. ZIKV infection in mice showed persistent viral replication in the eye tissue, suggesting that NMOSD symptoms are consequence of viral infection of the optic nerve cells.

Helicobacter pylori Infection and Extragastric Diseases-A Focus on the Central Nervous System

Helicobacter pylori (H. pylori) is most known to cause a wide spectrum of gastrointestinal impairments; however, an increasing number of studies indicates that H. pylori infection might be involved in numerous extragastric diseases such as neurological, dermatological, hematologic, ocular, cardiovascular, metabolic, hepatobiliary, or even allergic diseases. In this review, we focused on the nervous system and aimed to summarize the findings regarding H. pylori infection and its involvement in the induction/progression of neurological disorders. Neurological impairments induced by H. pylori infection are primarily due to impairments in the gut-brain axis (GBA) and to an altered gut microbiota facilitated by H. pylori colonization. Currently, regarding a potential relationship between Helicobacter infection and neurological disorders, most of the studies are mainly focused on H. pylori.

Systematic review of cases of acute myelitis in individuals with COVID-19

Background and purpose

An incremental number of cases of acute transverse myelitis (ATM) in individuals with ongoing or recent coronavirus disease 2019 (COVID‐19) have been reported.

Methods

A systematic review was performed of cases of ATM described in the context of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection by screening both articles published and in preprint.

Results

Twenty cases were identified. There was a slight male predominance (60.0%) and the median age was 56 years. Neurological symptoms first manifested after a mean of 10.3 days from the first onset of classical, mostly respiratory symptoms of COVID‐19. Overall, COVID‐19 severity was relatively mild. Polymerase chain reaction of cerebrospinal fluid for SARS‐CoV‐2 was negative in all 14 cases examined. Cerebrospinal fluid findings reflected an inflammatory process in most instances (77.8%). Aquaporin‐4 and myelin oligodendrocyte protein antibodies in serum (tested in 10 and nine cases, respectively) were negative. On magnetic resonance imaging, the spinal cord lesions spanned a mean of 9.8 vertebral segments, necrotic‐hemorrhagic transformation was present in three cases and two individuals had additional acute motor axonal neuropathy. More than half of the patients received a second immunotherapy regimen. Over a limited follow‐up period of several weeks, 90% of individuals recovered either partially or near fully.

Conclusion

Although causality cannot readily be inferred, it is possible that cases of ATM occur para‐ or post‐infectiously in COVID‐19. All identified reports are anecdotal and case descriptions are heterogeneous. Whether the condition and the observed radiological characteristics are specific to SARS‐CoV‐2 infection needs to be clarified.

Role of microbiota-derived short-chain fatty acids in nervous system disorders

During the past decade, accumulating evidence from the research highlights the suggested effects of bacterial communities of the human gut microbiota and their metabolites on health and disease. In this regard, microbiota-derived metabolites and their receptors, beyond the immune system, maintain metabolism homeostasis, which is essential to maintain the host's health by balancing the utilization and intake of nutrients. It has been shown that gut bacterial dysbiosis can cause pathology and altered bacterial metabolites' formation, resulting in dysregulation of the immune system and metabolism. The short-chain fatty acids (SCFAs), such as butyrate, acetate, and succinate, are produced due to the fermentation process of bacteria in the gut. It has been noted remodeling in the gut microbiota metabolites associated with the pathophysiology of several neurological disorders, such as Alzheimer's disease, multiple sclerosis, Parkinson's disease, amyotrophic lateral sclerosis, stress, anxiety, depression, autism, vascular dementia, schizophrenia, stroke, and neuromyelitis optica spectrum disorders, among others. This review will discuss the current evidence from the most significant studies dealing with some SCFAs from gut microbial metabolism with selected neurological disorders.

Epstein-Barr virus infection in a woman with aquaporin-4 seropositive neuromyelitis optica

Neuromyelitis optica spectrum disorders (NMOSD) are characterised by pathological antibodies to aquaporin-4 water channels of astrocytes, resulting in severe brain and spinal cord injury. Serological evidence suggests that Epstein-Barr virus (EBV) reactivation may contribute to their pathogenesis. We describe an unusual case of a woman with fever, rash and headache preceding an Aquaporin-4 antibody positive longitudinally extensive transverse myelitis. EBV was detected in her cerebrospinal fluid by polymerase chain reaction assay. This case highlights the potential role of EBV in the pathogenesis of NMOSD.

Targeting interleukin-6 to treat neuromyelitis optica spectrum disorders: Implications from immunology, the FcRn pathway and clinical experience

Neuromyelitis optica spectrum disorder (NMOSD) is a rare disease of the central nervous system (CNS) that is associated with poor outcomes for patients. Until recently, when complement inhibitors were approved, there was no approved therapy. Most recently, clinical trials of interleukin-6 (IL-6) blockade showed a therapeutic benefit for NMOSD. In this review, we introduce the immunological basis of IL-6 blockade in NMOSD and summarize current knowledge about the clinical use of the IL-6 receptor inhibitors tocilizumab and satralizumab. The aim of extending the half-life of monoclonal antibodies (mAbs) has been actualized by successful clinical translation for Satralizumab, achieved via the neonatal Fc receptor (FcRn) pathway. The basic principles of FcRn are highlighted in this review together with the potential therapeutic benefits of this emerging technology.

Covid-19 infection-induced neuromyelitis optica: a case report

INTRODUCTION

Acute respiratory syndrome coronavirus-2 (Covid-19) can infect the respiratory system, as well as the central, peripheral nervous system, and muscles, leading to neurological symptoms and signs. The most common neurological symptoms are dizziness, headache, impaired consciousness, ataxia, hypogosis, hyposmia, neuralgia, and myalgia. The most common neurological diseases are acute cerebrovascular disease, epilepsy, acute hemorrhagic necrotizing encephalopathy, miyelitis, and Gullian-Barre syndrome.

METHODS

In this case report, a patient infected with Covid-19 and diagnosed as neuromyelitis optica (NMO) with anamnesis, clinical and radiological findings is presented.

RESULTS

A 50-year-old woman presented with weakness of both legs, urine retention, high fever, and cough. Spinal magnetic resonance imaging revealed expensive long-segment and centrally located demyelinating lesion extending from the cervical cord (at the level of C3) to the conus. Thoracic-computerized tomography revealed consolidation areas located on the lower segments of bilateral lungs and ground-glass density, air bronchograms, and peribronchial thickening surrounding these areas. Aquaporin-4 immune globulin-G was found to be positive.

CONCLUSION

It was considered appropriate to present this case because of being the first case of parainfectious NMO considered to be induced by SARS-CoV-2.

Neuromyelitis Optica Presenting as Infectious Meningoencephalitis: Case Report and Literature Review

In this patient-focused review, we present a 34-year-old previously healthy man admitted for fever and headache two weeks after a motor vehicle accident. On admission, his workup was concerning for meningoencephalitis based on elevated cerebrospinal fluid (CSF) white blood cell count and elevated CSF protein. He was admitted for management of meningoencephalitis. During his course, no causative infectious agent was identified despite an extensive workup. He additionally underwent an autoimmune and paraneoplastic workup that was negative. During his hospitalization, he developed acute transverse myelitis manifested by bilateral lower extremity paralysis. After four weeks marked by persistent clinical deterioration, brain biopsy was performed. Pathologic examination was consistent with neuromyelitis optica spectrum disorder (NMOSD). In this case report and literature review, we explore the presentations of NMOSD that mimic an infection. Clinicians should be aware of the possibility of NMOSD masquerading as infectious meningoencephalitis or acute transverse myelitis.

Cytokines in CAR T Cell-Associated Neurotoxicity

Chimeric antigen receptor (CAR) T cells provide new therapeutic options for patients with relapsed/refractory hematologic malignancies. However, neurotoxicity is a frequent, and potentially fatal, complication. The spectrum of manifestations ranges from delirium and language dysfunction to seizures, coma, and fatal cerebral edema. This novel syndrome has been designated immune effector cell-associated neurotoxicity syndrome (ICANS). In this review, we draw an arc from our current understanding of how systemic and potentially local cytokine release act on the CNS, toward possible preventive and therapeutic approaches. We systematically review reported correlations of secreted inflammatory mediators in the serum/plasma and cerebrospinal fluid with the risk of ICANS in patients receiving CAR T cell therapy. Possible pathophysiologic impacts on the CNS are covered in detail for the most promising candidate cytokines, including IL-1, IL-6, IL-15, and GM-CSF. To provide insight into possible final common pathways of CNS inflammation, we place ICANS into the context of other systemic inflammatory conditions that are associated with neurologic dysfunction, including sepsis-associated encephalopathy, cerebral malaria, thrombotic microangiopathy, CNS infections, and hepatic encephalopathy. We then review in detail what is known about systemic cytokine interaction with components of the neurovascular unit, including endothelial cells, pericytes, and astrocytes, and how microglia and neurons respond to systemic inflammatory challenges. Current therapeutic approaches, including corticosteroids and blockade of IL-1 and IL-6 signaling, are reviewed in the context of what is known about the role of cytokines in ICANS. Throughout, we point out gaps in knowledge and possible new approaches for the investigation of the mechanism, prevention, and treatment of ICANS.

Herpes Zoster Radiculomyelitis With Aquaporin-4 Antibodies: A Case Report and Literature Review

Background: The relationship between varicella-zoster virus (VZV)-associated myelitis and aquaporin-4 immunoglobulin-G (AQP4-IgG) remains unknown.

Case Report: We report a case of acute radiculomyelitis with longitudinal extensive hyperintensity signals traversing the brainstem until the upper thoracic cord in a 55-year-old healthy woman following herpes zoster infection in the left C4-T3 dermatome. VZV-specific IgG in the cerebrospinal fluid (CSF) and AQP4-IgG positivity on enzyme-linked immunosorbent assay (ELISA) were undetectable. Thus, she was diagnosed with immune-competent VZV radiculomyelitis. Forty-two months later, she experienced a relapse, and AQP4-IgG positivity was detected on ELISA. A cell-based assay (CBA) showed AQP4-IgG positivity not only at the time of recurrence but also retrospectively at 1 month after the initial symptoms. We concluded that AQP4-IgG-positive neuromyelitis optica spectrum disorder (NMOSD) was concurrent with VZV myelitis. After the second attack, she was treated with azathioprine and has had no relapse since then.

Conclusion: We reported a case of VZV radiculomyelitis with confirmed concurrent AQP4-IgG positivity. NMOSD induced by herpes zoster has been recently identified, but distinguishing it from VZV myelitis can be difficult and whether these two diseases aggravate each other is unknown. Awareness of the potentially varied presentation of VZV myelitis can enable earlier recognition and proper treatment.

Neuromyelitis optica spectrum disorders

The disease concept of Neuromyelitis Optica Spectrum Disorders(NMOSD) has undergone a significant change over the last two decades including the detection of Myelin Oligodendrocyte Glycoprotein(MOG) antibody in patients who are seronegative for aquaporin-4 antibody. Aquaporin-4 antibody positive NMOSD is now regarded as an immune astrocytopathy. Conversely, MOG antibody associated disease is known to target myelin rather than astrocytes, leading to an NMOSD syndrome with distinct clinical and radiological features. Incorporation of clinical features like area postrema syndrome, brainstem syndrome, diencephalic syndrome and cortical manifestations as core clinical characteristics into the revised diagnostic criteria has widened the clinical spectrum of NMOSD. With the development of these criteria, it is possible to make the diagnosis at an earlier stage so that effective immunosuppression can be instituted promptly for a better long-term prognosis. Newer therapeutic agents have been introduced for aquaporin-4 seropositive NMOSD disease; however, challenges remain in treating seronegative disease because of limited treatment options.

A case of area postrema variant of neuromyelitis optica spectrum disorder following SARS-CoV-2 infection

Neuromyelitis optica spectrum disorder (NMOSD) is a disabling autoimmune astrocytopathic channelopathy, characterized by the presence of pathogenic antibodies to aquaporin-4 (AQP-4) water channels. Several viral infections including HIV, influenza virus, varicella zoster virus, and Epstein Barr virus, among others, have been alleged to trigger NMOSD in both immunocompetent and immunocompromised individuals. Neurological manifestations of coronavirus infectious disease of 2019 (COVID-19) have been ever evolving and the spectrum of neuraxial involvement is broadening. Albeit it may affect any area of the neural axis, the involvement of the spinal cord is rare compared to that of the brain and of the peripheral nervous system. Cases with acute longitudinally extensive transverse myelitis (LETM) have been recently reported in SARS-CoV-2 infection but did not fulfill the international consensus diagnostic criteria for NMOSD. AQP-4-antibody-seropositive NMOSD following SARS-CoV-2 infection had not yet been reported. We herein report a novel case of a previously healthy man who presented with a clinical picture of bouts of vomiting and hiccoughs (area postrema syndrome), which rapidly evolved to acute LETM, all following SARS-CoV-2 infection. He was finally diagnosed to be a case of seropositive NMOSD which presented as area postrema syndrome. The response to immunomodulatory drugs was excellent.

Risk of relapse in patients with neuromyelitis optica spectrum disorder: Recognition and preventive strategy

Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune inflammatory disorder of the central nervous system (CNS) that is mainly associated with serum autoantibodies against aquaporin-4 (AQP4) in astrocytes. The relapsing clinical course of NMOSD, which can be blinding and disabling due to severe visual impairment, spinal cord lesions and a group of brain syndromes, suggests the importance of accurately evaluating the likelihood and severity of relapse at an early stage of the disease. To date, many risk factors have been revealed in association with relapse, and only some of them are supported by substantial evidence. Furthermore, while the clinical use of conventional immunosuppressants is mostly empirical, an increasing number of emerging therapies for monoclonal antibodies have been confirmed by several randomized placebo-controlled trials to be effective and safe for relapse prevention. In this review, we summarize the reported risk factors that may influence the frequency, symptoms, severity and prognosis of relapse in NMOSD, as well as the efficacy and safety of emerging therapies for relapse prevention. All of these results enable us to better recognize patients who are at higher risk of relapse and suggest more effective monoclonal antibody therapies for use in these patients.

Varicella Zoster Reactivation Causing Aseptic Meningitis in Healthy Adolescents: A Case Series And Review Of The Literature

We describe 3 cases of adolescent varicella-zoster virus reactivation, complicated by aseptic meningitis, presenting to our institution in a 3-year period. These cases highlight varicella-zoster virus reactivation as an important cause of aseptic meningitis in the differential diagnosis of healthy adolescents, even in the absence of a characteristic exanthem. Evidence-based management recommendations are needed.

Neuromyelitis Optica Spectrum Disorder Attack Triggered by Herpes Zoster Infection

Neuromyelitis optica spectrum disorder is a severe autoimmune disease of the central nervous system characterized by recurrent inflammatory events primarily involving the optic nerves and spinal cord. Recently, a triggering role of infectious events in the development of NMOSD has been suggested. Varicella zoster virus is the most common viral infection involved, though the linkage with anti-aquaporin-4 antibodies is so far unknown. We report, to the best of our knowledge, the first pediatric case report about NMOSD relapse triggered by herpes zoster infection. The strict temporal relationship between VZV infection and NMO attacks seems to be more than simply due to chance; however, further reports are needed to be confirmed.

Role of Methyl Prednisolone in Longitudinal Extensive Transverse Myelitis (LETM) in Children

Objective:

The role of methyl prednisolone in longitudinal extensive transverse myelitis in children is not completely discovered in developing country like Pakistan. So this is the first study which aimed to evaluate the efficacy of methyl prednisolone in longitudinal extensive transverse myelitis in children.

Methods:

This is quasi experimental hospital based descriptive prospective study. The data was collected from 34 children admitted in Paediatric Neurology department through Outpatient/emergency department in Children’s Hospital and the Institute of Child Health, Lahore for period of one year from January 2018 to December 2018. The children full filling the inclusion criteria were observed before and after giving injection methyl prednisolone 30mg/kg/dose (maximum dose one Gram irrespective of the body weight) once daily for five days in the form of intravenous infusion.

Results:

Complete recovery was seen in 41.2% while 58.8% showed partial recovery. The correlation of response to treatment (recovery) with gender, area of spinal cord involvement, muscle power and autonomic dysfunction is found at significance level of five percent according to Chi square test.

Conclusion:

Early consideration and administration of methyl prednisolone in longitudinally extensive transverse myelitis in children can be beneficial and can help to reduce the morbidity.

Neuromyelitis optica spectrum disorder and active tuberculosis

Tuberculosis is on the rise again. It brings with it potential for neurological involvement both as a direct infection and as a parainfectious process. Accordingly we report the development of neurological problems affecting a 48-year-old patient's vision and sensation while being treated for active tuberculosis. At its nadir her vision deteriorated to nil perception of light and she had a sensory level to T10. Neuromyelitis optica spectrum disorder was diagnosed. We discuss our management strategy with neuromodulation in the context of active tuberculosis infection.

Magnetic resonance imaging in immune-mediated myelopathies

Immune-mediated myelopathies are a heterogeneous group of inflammatory spinal cord disorders including autoimmune disorders with known antibodies, e.g. aquaporin-4 IgG channelopathy or anti-myelin oligodendrocyte glycoprotein-associated myelitis, myelopathies in the context of multiple sclerosis and systemic autoimmune disorders with myelopathy, as well as post-infectious and paraneoplastic myelopathies. Although magnetic resonance imaging of the spinal cord is still challenging due to the small dimension of the cord cross-section and frequent movement and susceptibility artifacts, recent methodological advances have led to improved diagnostic evaluation and characterization of immune-mediated myelopathies. Topography, length and width of the lesion, gadolinium enhancement pattern, and changes in morphology over time help in narrowing the broad differential diagnosis. In this review, we give an overview of recent advances in magnetic resonance imaging of immune-mediated myelopathies and its role in the differential diagnosis and monitoring of this heterogeneous group of disorders.

Anti-aquaporin-4 Antibody Positive Optic Neuritis Following Scrub Typhus in an Elderly Female

INTRODUCTION

Aquaporin-4 antibody (AQP4-Ab) is specific for neuromyelitis optica spectrum disorder (NMOSD) and so is helpful to distinguish NMOSD from other autoimmune diseases. Several viral infections may play a role in the onset of NMOSD.

CASE REPORT

We describe a case of a previous healthy 82-year-old woman who presented with acute visual loss occurring 3 weeks after scrub typhus. Physical examination showed a relatively afferent pupillary defect in the right eye and ophthalmoscopy revealed edema of the right optic disc. Enhanced magnetic resonance imaging revealed enhancement of the right optic nerve. Serological testing showed AQP4-Ab. After methylprednisolone pulse therapy followed by oral tapering of prednisolone, visual dysfunction was improved. Subsequently she experienced no attacks for 5 years.

CONCLUSIONS

Optic neuritis (ON) associated with scrub typhus is extremely rare. Our case support that scrub typhus could trigger ON in a lifelong asymptomatic patient with AQP4-Ab and AQP4-Ab should be considered in a very old age patient with suspected postinfectious inflammatory ON.

Epstein - Barr virus Infection in a Patient with Neuromyelitis Optica Spectrum Disorder and Sjögren's Syndrome: A Case Report and Review of Literature

BACKGROUND

The association of Neuromyelitis Optica Spectrum Disorders (NMOSD) with autoimmune disorders including Sjögren's syndrome (SS), is well recognized. Epstein Barr virus (EBV) has been associated to various neurological entities. We describe a case where EBV infection likely preceded NMOSD in a patient with unrecognized SS. The clinical features, work up and management are described.

CASE PRESENTATION

A 40-year woman with history of stroke and Guillain-Barre Syndrome (GBS) two years prior, presented with progressive lower extremity weakness and pain. Brain MRI revealed hyperintensities in the cerebellar and parietal lobes consistent with old infarcts, high intensity signal in the white matter and enhancing intramedullary lesion at the level of T2 and the conus medullaris. Cerebrospinal fluid (CSF) revealed no oligoclonal bands. Next day, the patient developed right ankle weakness and urinary incontinence. NMOSD was suspected and pulse steroids initiated. Patient's weakness resolved. Antinuclear antibodies (ANA), anti-SSA/SSB and Aquaporin 4 antibodies (AQP4Ab) were positive. CSF was positive for EBV. Parotid gland ultrasound revealed non-homogeneous tissue.Ganciclovir and plasmapheresis were started. The patient's sensation and motor deficits improved and one month after, she had regained motor power and sphincter control. The patient was discharged on oral prednisone and plans for rituximab infusions.On follow-up imaging, Spinal MRI showed areas of myelomalacia and complete resolution at the level of T2 and conus medularis lesions respectively. The patient had no additional flares, but did complain of chronic neuropathic pain.

CONCLUSION

NMOSD commonly coexist with other autoimmune diseases. The association of SS and NMOSD is well recognized. EBV infections can present with neurological manifestations however, EBV has also been linked to the development of autoimmunity. In our case, EBV was detected in CSF and antiviral therapy was initiated in addition to the treatment modalities for NMOSD which led to a full recovery in our patient.

Long-term outcomes of varicella zoster virus infection-related myelitis in 10 immunocompetent patients

OBJECTIVE

To describe the clinical presentation and long-term disease outcomes of varicella zoster virus (VZV) infection-related myelitis (VZVM) in immunocompetent patients.

METHOD

A series of 10 immunocompetent patients with VZVM were retrospectively observed and followed (3-96 months).

RESULTS

The onset of myelitis was timed in relation to the appearance of VZV-associated rash (-3 to 50 days). Rash locations included the cervical (5), thoracic (2), and lumbar (3) dermatomes, whereas myelitis localized to the cervical (6) and thoracic (9) spinal cord and the medulla (1). Spinal MRI revealed extensive longitudinal transverse myelitis in nine patients, with multiple segmental lesions (≥2 segments) evident in five patients. Aquaporin-4, myelin oligodendrocyte glycoprotein, ganglioside Q1b, and ganglioside T1b antibodies were detected in some patients. Three patients fulfilled the 2015 diagnostic criteria for neuromyelitis optica spectrum disease, of whom two relapsed. Seven patients were treated with intravenous antivirals and methylprednisolone, with the remaining three patients receiving methylprednisolone only. Ongoing immunosuppressive therapy was provided for two patients who experienced relapses. To date, no patients have reported VZV reactivation. Over the course of follow-up, the Expanded Disability Status Scale (EDSS) score deceased from 4.9 to 2.6 on average.

CONCLUSIONS

VZVM runs a relatively benign course in immunocompetent patients, although relapses can occur depending on patient immune status. A comprehensive evaluation of patient's autoimmune condition is recommended.

SLE presenting as demyelinative autoimmune visual loss

A healthy 38-year-old woman developed sudden unilateral vision loss due to retrobulbar optic neuritis in the wake of varicella-zoster virus infection. She had no further central nervous system (CNS) lesions. Antinuclear antibodies (ANA) and anti-aquaporin 4 antibodies were found, consistent with neuromyelitis optica (NMO). Later, serial MRIs showed dynamic short-segment and long-segment myelitis lesions, ANA titre increased and additional autoantibodies were found including anti-dsDNA, anti-chromatin/nucleosome and antiphospholipid antibodies. In that setting, NMO can be regarded a rare presenting manifestation of systemic lupus erythematosus (SLE). The relevant literature is reviewed and the implications of NMO spectrum disorder demyelinating syndromes as the first manifestation of SLE (with or without antiphospholipid syndrome) (APS) or their later development (in a patient diagnosed with SLE) as part of the spectrum of neuropsychiatric SLE are analysed in view of recent research developments in the field.

Neuromyelitis optica spectrum disorder associated with dengue virus infection

Dengue virus infection is a disease with high incidence in some tropical and subtropical countries. A variety of neurological complications of dengue fever (DF) has been described including two cases with the phenotype of neuromyelitis optica spectrum disorder (NMOSD). However, aquaporin-4 serostatus was unknown or negative in these patients. We report two patients with NMOSD occurring in association with DF. The first patient presented with brainstem symptoms and the second one with isolated unilateral optic neuritis. Both patients tested positive for serum AQP4-antibody. This report shows that DF may trigger seropositive NMOSD.

Longitudinally extensive transverse myelitis with pulmonary tuberculosis: Two case reports

RATIONALE

Longitudinally extensive transverse myelitis (LETM) is characterized by contiguous inflammatory lesions of spinal cord extending to ≥3 vertebral segments. The etiology of LETM is complicated, including various infection, autoimmune disease, and so on. Neuromyelitis optic spectrum disorder (NMOSD) is the most common cause of LETM. Several case reports have suggested the associations between NMOSD and pulmonary tuberculosis (PTB).

PATIENT CONCERNS

Patient 1, a 20-year-old woman who had a past history of PTB, presented with weakness, numbness, and pain in the limbs. The serum anti-aquaporin-4 antibody (AQP4-Ab) was strongly positive, and the magnetic resonance imaging (MRI) scan of cervical and thoracic spinal cord after admission to the hospital revealed hyperintensity lesions extending from C3 to T8 on T2-weighted (T2W) image, T1-weighted (T1W) image, and fluid-attenuated inversion recovery (FLAIR) image. Patient 2, a 21-year-old woman who had a past medical history of PTB without receiving any treatment, presented for numbness in bilateral lower limbs and in the chest. The anti-AQP4-Ab was negative both in the serum and in the cerebral spinal fluid (CSF) of the patient. The MRI scan during hospitalization of cervical and thoracic spinal cord revealed diffuse hyperintense signal extending C3 to T11 on T2W and FLAIR images and hypointense signal on T1W image.

DIAGNOSIS

The first patient was diagnosed with anti-AQP4-Ab positive NMOSD, while the second case was an anti-AQP4-Ab negative LETM patient.

INTERVENTIONS

Both of the patients received a combination of corticosteroid and anti-tuberculosis (isonicotinyl hydrazide 0.3 g/d, rifampin 0.45 g/d, pyrazinamide 1 g/d, and ethambutol 1 g/d) treatment.

OUTCOMES

The patients were followed up for up to 1 year. The Expanded Disability Status Scale (EDSS) of both patients were decreased and the lesion size in the spinal cord was significantly reduced at the time point of the follow-up.

LESSONS

Combination of anti-tuberculosis and corticosteroid treatment may have better prognosis for patient of LETM with PTB.

The Gut Microbiome in Neuromyelitis Optica

Neuromyelitis optica (NMO) is a rare, disabling, sometimes fatal central nervous system inflammatory demyelinating disease that is associated with antibodies ("NMO IgG") that target the water channel protein aquaporin-4 (AQP4) expressed on astrocytes. There is considerable interest in identifying environmental triggers that may elicit production of NMO IgG by AQP4-reactive B cells. Although NMO is considered principally a humoral autoimmune disease, antibodies of NMO IgG are IgG1, a T-cell-dependent immunoglobulin subclass, indicating that AQP4-reactive T cells have a pivotal role in NMO pathogenesis. When AQP4-specific proliferative T cells were first identified in patients with NMO it was discovered that T cells recognizing the dominant AQP4 T-cell epitope exhibited a T helper 17 (Th17) phenotype and displayed cross-reactivity to a homologous peptide sequence within a protein of Clostridium perfringens, a commensal bacterium found in human gut flora. The initial analysis of gut microbiota in NMO demonstrated that, in comparison to healthy controls (HC) and patients with multiple sclerosis, the microbiome of NMO is distinct. Remarkably, C. perfringens was the second most significantly enriched taxon in NMO, and among bacteria identified at the species level, C. perfringens was the one most highly associated with NMO. Those discoveries, along with evidence that certain Clostridia in the gut can regulate the balance between regulatory T cells and Th17 cells, indicate that gut microbiota, and possibly C. perfringens itself, could participate in NMO pathogenesis. Collectively, the evidence linking microbiota to humoral and cellular immunity in NMO underscores the importance for further investigating this relationship.

Infections in neuromyelitis optica spectrum disorder

Neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory astrocytopathy that has both genetic and environmental causes. A growing body of evidence suggests that the presence of several infectious agents correlates with the development of NMOSD. In this review, we summarize studies that either support or present evidence against the hypothesized association between infection and NMOSD. We will also present an overview of potential mechanisms underlying the pathogenesis of NMOSD. Finally, we provide some beneficial properties that infectious elements may have based on "hygiene hypothesis". It is of great clinical significance to further investigate the complex mechanisms by which infections may affect autoimmune diseases to develop better strategies to prevent and treat them, although so far no causal link between infectious agents and NMOSD has been established.