Update on biomarkers in neuromyelitis optica

Neuromyelitis optica (NMO) (and NMO spectrum disorder) is an autoimmune inflammatory disease of the CNS primarily affecting spinal cord and optic nerves. Reliable and sensitive biomarkers for onset, relapse, and progression in NMO are urgently needed because of the heterogeneous clinical presentation, severity of neurologic disability following relapses, and variability of therapeutic response. Detecting aquaporin-4 (AQP4) antibodies (AQP4-IgG or NMO-IgG) in serum supports the diagnosis of seropositive NMO. However, whether AQP4-IgG levels correlate with disease activity, severity, response to therapy, or long-term outcomes is unclear. Moreover, biomarkers for patients with seronegative NMO have yet to be defined and validated. Collaborative international studies hold great promise for establishing and validating biomarkers that are useful in therapeutic trials and clinical management. In this review, we discuss known and potential biomarkers for NMO.

Neuromyelitis optica and multiple sclerosis: Seeing differences through optical coherence tomography

Neuromyelitis optica (NMO) is an inflammatory autoimmune disease of the central nervous system that preferentially targets the optic nerves and spinal cord. The clinical presentation may suggest multiple sclerosis (MS), but a highly specific serum autoantibody against the astrocytic water channel aquaporin-4 present in up to 80% of NMO patients enables distinction from MS. Optic neuritis may occur in either condition resulting in neuro-anatomical retinal changes. Optical coherence tomography (OCT) has become a useful tool for analyzing retinal damage both in MS and NMO. Numerous studies showed that optic neuritis in NMO typically results in more severe retinal nerve fiber layer (RNFL) and ganglion cell layer thinning and more frequent development of microcystic macular edema than in MS. Furthermore, while patients’ RNFL thinning also occurs in the absence of optic neuritis in MS, subclinical damage seems to be rare in NMO. Thus, OCT might be useful in differentiating NMO from MS and serve as an outcome parameter in clinical studies.

Idiopathic aquaporin-4 antibody negative longitudinally extensive transverse myelitis

Background:

Longitudinally extensive transverse myelitis (LETM) is a characteristic manifestation of neuromyelitis optica (NMO). However, not all patients with LETM are positive for aquaporin-4 (AQP4) antibodies. We evaluated the characteristics of idiopathic isolated LETM negative for AQP4 antibodies.

Methods:

From the National Cancer Center registry of inflammatory diseases of the central nervous system, patients with LETM as an initial manifestation and follow-up for at least two years were enrolled. Their medical records and MRIs were reviewed retrospectively. AQP4 antibody was confirmed by three different validated methods at least three times. Cerebrospinal fluid (CSF) glial fibrillary acidic protein (GFAP) levels were measured to investigate astrocyte damage.

Results:

Among 108 patients with first-ever LETM, 55 were positive for AQP4 antibodies (P-LETM) and 53 were consistently negative. Of them, seven were later diagnosed with seronegative NMO, and four were positive for MOG antibodies. The remaining 42 patients (N-LETM) showed several features distinct from P-LETM: male predominance, older age of onset, milder clinical presentation, spinal cord confinement and absence of combined autoimmunity. CSF GFAP levels were not increased in N-LETM but were markedly elevated in P-LETM.

Conclusions:

Idiopathic isolated N-LETM is not that rare among first-ever LETM, and has many features distinct from P-LETM where astrocytic damage is evident.

Severe demyelination but no astrocytopathy in clinically definite neuromyelitis optica with anti-myelin-oligodendrocyte glycoprotein antibody

We report a patient with neuromyelitis optica (NMO) presenting anti-myelin-oligodendrocyte glycoprotein (MOG)-seropositive, in whom biomarkers of demyelination and astrocyte damage were measured during an acute attack. A 31-year-old man developed right optic neuritis followed by longitudinally extensive transverse myelitis, fulfilling the criteria for definite NMO. He was anti-MOG-seropositive and anti-aquaporin-4 seronegative. The myelin basic protein level was markedly elevated whereas glial fibrillary acidic protein was not detectable in cerebrospinal fluid during an acute attack. His symptoms quickly improved after high-dose methylprednisolone therapy. This case suggests that NMO patients with anti-MOG may have severe demyelination in the absence of astrocyte injury.

Cerebrospinal fluid aquaporin-4 antibody levels in neuromyelitis optica attacks

To elucidate immunopathogenetic roles of aquaporin-4 antibodies in the cerebrospinal fluid (CSF) of neuromyelitis optica spectrum disorders (NMOSD), we analyzed aquaporin-4 antibody titers, cellular and inflammatory markers in the CSF collected from 11 aquaporin-4 antibody seropositive patients. The CSF aquaporin-4 antibody levels during attacks (but not in sera) closely correlated with pleocytosis, inflammatory cytokines including interleukin-6 that can regulate antibody-producing plasmablasts, and glial fibrillary acidic protein levels in the CSF. The amount of aquaporin-4 antibodies present in the central nervous system may have therapeutic implications, as it is associated with astrocyte injury and inflammatory responses during NMOSD attacks. Ann Neurol 2014;76:305–309

Seronegative Neuromyelitis Optica Spectrum - The challenges on disease definition and pathogenesis

Neuromyelitis optica spectrum disorders (NMOSD) are characterized by severe optic neuritis and/or longitudinally extensive transverse myelitis, and some brain lesions are also unique to NMOSD. Serum autoantibodies against aquaporin-4 (AQP4) are detected in most cases of NMOSD. However, some patients with NMOSD remain seronegative despite repetitive testing during attacks with highly sensitive cell-based assays. The differential diagnosis of NMOSD is not restricted to multiple sclerosis and it includes many diseases that can produce longitudinally extensive myelitis and/or optic neuritis. We review the clinical features, imaging, and laboratory findings that can be helpful on the diagnostic work-up, discuss the differences between AQP4 antibody positive and negative patients with NMOSD, including features of NMOSD with antibodies against myelin oligodendrocyte glycoprotein.

Changes in Th17 and regulatory T cells after fingolimod initiation to treat multiple sclerosis

Fingolimod has demonstrated efficacy in patients with multiple sclerosis (MS), and patients become gradually lymphopenic after a few days of treatment, with selective reductions in CD4+ subsets. We observed an increase in the frequencies of circulating regulatory T cells after fingolimod administration. However, we also found that half of patients had increased proportion of circulating Th17 cells in CD4+ T cells after treatment (including a patient with MS relapses), whereas the others showed lower frequencies of Th17 cells, indicating some variability among patients. Further studies may confirm if slower reduction of circulating Th17 cells following fingolimod initiation predisposes to relapses.

Distinction between MOG antibody-positive and AQP4 antibody-positive NMO spectrum disorders

OBJECTIVE

To evaluate clinical features among patients with neuromyelitis optica spectrum disorders (NMOSD) who have myelin oligodendrocyte glycoprotein (MOG) antibodies, aquaporin-4 (AQP4) antibodies, or seronegativity for both antibodies.

METHODS

Sera from patients diagnosed with NMOSD in 1 of 3 centers (2 sites in Brazil and 1 site in Japan) were tested for MOG and AQP4 antibodies using cell-based assays with live transfected cells.

RESULTS

Among the 215 patients with NMOSD, 7.4% (16/215) were positive for MOG antibodies and 64.7% (139/215) were positive for AQP4 antibodies. No patients were positive for both antibodies. Patients with MOG antibodies represented 21.1% (16/76) of the patients negative for AQP4 antibodies. Compared with patients with AQP4 antibodies or patients who were seronegative, patients with MOG antibodies were more frequently male, had a more restricted phenotype (optic nerve more than spinal cord), more frequently had bilateral simultaneous optic neuritis, more often had a single attack, had spinal cord lesions distributed in the lower portion of the spinal cord, and usually demonstrated better functional recovery after an attack.

CONCLUSIONS

Patients with NMOSD with MOG antibodies have distinct clinical features, fewer attacks, and better recovery than patients with AQP4 antibodies or patients seronegative for both antibodies.

Aquaporin-4 antibody-positive myelitis initially biopsied for suspected spinal cord tumors: diagnostic considerations

Two patients with longitudinally extensive myelopathy were initially biopsied for suspected spinal cord tumors. Both patients were later diagnosed with neuromyelitis optica spectrum disorders (NMOSD) supported by their AQP4-seropositivity. Pathological review of both biopsies revealed demyelinated lesions with thickened vessel walls and tissue rarefaction. Immunohistochemical staining demonstrated findings compatible with acute NMOSD lesions in one case while the other case exhibited findings consistent with chronic NMOSD lesions. A pre-biopsy differential diagnosis of longitudinally extensive spinal cord tumors should include NMOSD. Specific biopsy features, such as cystic changes with vascular wall thickening and astrocyte injury, should raise suspicion for NMOSD.

Current concept of neuromyelitis optica (NMO) and NMO spectrum disorders

Neuromyelitis optica (NMO) has been described as a disease clinically characterised by severe optic neuritis (ON) and transverse myelitis (TM). Other features of NMO include female preponderance, longitudinally extensive spinal cord lesions (>3 vertebral segments), and absence of oligoclonal IgG bands . In spite of these differences from multiple sclerosis (MS), the relationship between NMO and MS has long been controversial. However, since the discovery of NMO-IgG or aquaporin-4 (AQP4) antibody (AQP4-antibody), an NMO-specific autoantibody to AQP4, the dominant water channel in the central nervous system densely expressed on end-feet of astrocytes, unique clinical features, MRI and other laboratory findings in NMO have been clarified further. AQP4-antibody is now the most important laboratory finding for the diagnosis of NMO. Apart from NMO, some patients with recurrent ON or recurrent longitudinally extensive myelitis alone are also often positive for AQP4-antibody. Moreover, studies of AQP4-antibody-positive patients have revealed that brain lesions are not uncommon in NMO, and some patterns appear to be unique to NMO. Thus, the spectrum of NMO is wider than mere ON and TM. Pathological analyses of autopsied cases strongly suggest that unlike MS, astrocytic damage is the primary pathology in NMO, and experimental studies confirm the pathogenicity of AQP4-antibody. Importantly, therapeutic outcomes of some immunological treatments are different between NMO and MS, making early differential diagnosis of these two disorders crucial. We provide an overview of the epidemiology, clinical and neuroimaging features, immunopathology and therapy of NMO and NMO spectrum disorders.

Aquaporin-4 antibody-positive cases beyond current diagnostic criteria for NMO spectrum disorders

OBJECTIVES

To analyze aquaporin-4 (AQP4) antibody-positive patients who do not fulfill the current diagnostic criteria of neuromyelitis optica (NMO) and NMO spectrum disorders (NMOSD).

METHODS

We used a cell-based assay (CBA) with AQP4-transfected cells to detect AQP4 antibody in 298 consecutive patients with inflammatory CNS disorders seen at Tohoku University Hospital from 2007 to 2012. The patients were diagnosed as NMO, NMOSD, multiple sclerosis, or others using the respective current diagnostic criteria. The seropositive samples by CBA were also tested using a commercial ELISA.

RESULTS

Seventy-two patients were AQP4 antibody positive. Among them, 18.1% (13/72) did not meet the NMO or NMOSD criteria (7 with monophasic optic neuritis, 2 with attacks restricted to the brainstem, and 4 with myelitis with less than 3 vertebral segments) and 84.6% (11/13) of these had only a single attack. The ELISA results were negative in 38.4% (5/13) of those patients, and they had lower antibody titers by CBA than patients with NMO/NMOSD. Although these patients had a shorter follow-up and few attacks, they shared some clinical features with NMO/NMOSD patients such as onset age, female predominance, presence of other autoantibodies, severe optic neuritis attacks, centrally located spinal cord lesions, persisting hiccups, and nausea or vomiting episodes.

CONCLUSIONS

AQP4 antibody-positive patients with single or recurrent attacks of optic neuritis, myelitis, or brain/brainstem disease not fulfilling the current criteria of NMO or NMOSD may not be uncommon, and they should also be included in the NMO spectrum.

Aquaporin-4 antibody-positive cases beyond current diagnostic criteria for NMO spectrum disorders

OBJECTIVES

To analyze aquaporin-4 (AQP4) antibody-positive patients who do not fulfill the current diagnostic criteria of neuromyelitis optica (NMO) and NMO spectrum disorders (NMOSD).

METHODS

We used a cell-based assay (CBA) with AQP4-transfected cells to detect AQP4 antibody in 298 consecutive patients with inflammatory CNS disorders seen at Tohoku University Hospital from 2007 to 2012. The patients were diagnosed as NMO, NMOSD, multiple sclerosis, or others using the respective current diagnostic criteria. The seropositive samples by CBA were also tested using a commercial ELISA.

RESULTS

Seventy-two patients were AQP4 antibody positive. Among them, 18.1% (13/72) did not meet the NMO or NMOSD criteria (7 with monophasic optic neuritis, 2 with attacks restricted to the brainstem, and 4 with myelitis with less than 3 vertebral segments) and 84.6% (11/13) of these had only a single attack. The ELISA results were negative in 38.4% (5/13) of those patients, and they had lower antibody titers by CBA than patients with NMO/NMOSD. Although these patients had a shorter follow-up and few attacks, they shared some clinical features with NMO/NMOSD patients such as onset age, female predominance, presence of other autoantibodies, severe optic neuritis attacks, centrally located spinal cord lesions, persisting hiccups, and nausea or vomiting episodes.

CONCLUSIONS

AQP4 antibody-positive patients with single or recurrent attacks of optic neuritis, myelitis, or brain/brainstem disease not fulfilling the current criteria of NMO or NMOSD may not be uncommon, and they should also be included in the NMO spectrum.

Neutralizing antibodies are associated with a reduction of interferon-β efficacy during the treatment of Japanese multiple sclerosis patients

Multiple sclerosis (MS) is a chronic immune-mediated inflammatory demyelinating disease of the central nervous system. Interferon-β (IFN-β) has been used as the first line therapy for MS treatment in Japan, but patients treated with IFN-β may develop antibodies, known as neutralizing antibodies (NAbs), which abrogate its therapeutic effects. Intramuscular IFN-β 1a and subcutaneous IFN-β 1b are currently available in Japan, but large-scale studies evaluating the prevalence and clinical implications of NAbs against these IFN-β preparations in MS patients have only been performed in Caucasian populations. NAbs positivity has been reported to be associated with HLA-DRB1 alleles, suggesting that the positivity might differ among populations with distinct genetic backgrounds. Clinical information and sera were collected from 229 consecutive MS patients treated with IFN-β in 4 centers in Japan. Sera were tested for NAbs using a luciferase reporter gene assay. In total, 5.2% of IFN-β-1a-treated patients (4/77) and 30.3% of IFN-β-1b-treated patients (46/152) were positive for Nabs. The frequency of NAbs was highest in patients treated for 13 to 24 months. Clinical relapse and contrast-enhancing lesions in the magnetic resonance imaging increased together with NAbs titers in this group. In conclusion, the prevalence of NAbs in Japanese MS patients is similar to that in Caucasian populations and is associated with an increase in disease activity. Therefore, routine NAbs testing is recommended also in Asian populations to ensure the early identification of patients who would benefit from a change in therapy.