Sean J. Pittock

A serum autoantibody marker of neuromyelitis optica: distinction from multiple sclerosis

BACKGROUND Neuromyelitis optica is an inflammatory demyelinating disease with generally poor prognosis that selectively targets optic nerves and spinal cord. It is commonly misdiagnosed as multiple sclerosis. Neither disease has a distinguishing biomarker, but optimum treatments differ. The relation of neuromyelitis optica to optic-spinal multiple sclerosis in Asia is uncertain. We assessed the capacity of a putative marker for neuromyelitis optica (NMO-IgG) to distinguish neuromyelitis optica and related disorders from multiple sclerosis. METHODS Indirect immunofluorescence with a composite substrate of mouse tissues identified a distinctive NMO-IgG staining pattern, which we characterised further by dual immunostaining. We tested masked serum samples from 102 North American patients with neuromyelitis optica or with syndromes that suggest high risk of the disorder, and 12 Japanese patients with optic-spinal multiple sclerosis. Control patients had multiple sclerosis, other myelopathies, optic neuropathies, and miscellaneous disorders. We also established clinical diagnoses for 14 patients incidentally shown to have NMO-IgG among 85000 tested for suspected paraneoplastic autoimmunity. FINDINGS NMO-IgG outlines CNS microvessels, pia, subpia, and Virchow-Robin space. It partly colocalises with laminin. Sensitivity and specificity were 73% (95% CI 60-86) and 91% (79-100) for neuromyelitis optica and 58% (30-86) and 100% (66-100) for optic-spinal multiple sclerosis. NMO-IgG was detected in half of patients with high-risk syndromes. Of 14 seropositive cases identified incidentally, 12 had neuromyelitis optica or a high-risk syndrome for the disease. INTERPRETATION NMO-IgG is a specific marker autoantibody of neuromyelitis optica and binds at or near the blood-brain barrier. It distinguishes neuromyelitis optica from multiple sclerosis. Asian optic-spinal multiple sclerosis seems to be the same as neuromyelitis optica.

IgG marker of optic-spinal multiple sclerosis binds to the aquaporin-4 water channel.

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease that selectively affects optic nerves and spinal cord. It is considered a severe variant of multiple sclerosis (MS), and frequently is misdiagnosed as MS, but prognosis and optimal treatments differ. A serum immunoglobulin G autoantibody (NMO-IgG) serves as a specific marker for NMO. Here we show that NMO-IgG binds selectively to the aquaporin-4 water channel, a component of the dystroglycan protein complex located in astrocytic foot processes at the blood-brain barrier. NMO may represent the first example of a novel class of autoimmune channelopathy.

The spectrum of neuromyelitis optica

Neuromyelitis optica (also known as Devics disease) is an idiopathic, severe, demyelinating disease of the central nervous system that preferentially affects the optic nerve and spinal cord. Neuromyelitis optica has a worldwide distribution, poor prognosis, and has long been thought of as a variant of multiple sclerosis; however, clinical, laboratory, immunological, and pathological characteristics that distinguish it from multiple sclerosis are now recognised. The presence of a highly specific serum autoantibody marker (NMO-IgG) further differentiates neuromyelitis optica from multiple sclerosis and has helped to define a neuromyelitis optica spectrum of disorders. NMO-IgG reacts with the water channel aquaporin 4. Data suggest that autoantibodies to aquaporin 4 derived from peripheral B cells cause the activation of complement, inflammatory demyelination, and necrosis that is seen in neuromyelitis optica. The knowledge gained from further assessment of the exact role of NMO-IgG in the pathogenesis of neuromyelitis optica will provide a foundation for rational therapeutic trials for this rapidly disabling disease.

Neuromyelitis optica IgG predicts relapse after longitudinally extensive transverse myelitis

We investigated whether neuromyelitis optica (NMO) IgG seropositivity at the initial presentation of longitudinally extensive transverse myelitis (LETM) predicts relapse of myelitis or development of optic neuritis.

Neuromyelitis optica and non organ-specific autoimmunity.

BACKGROUND Neuromyelitis optica (NMO) is often associated with other clinical or serological markers of non-organ-specific autoimmunity. OBJECTIVE To evaluate the relationship between NMO spectrum disorders (NMOSDs), including NMO, longitudinally extensive transverse myelitis, and recurrent optic neuritis, and autoimmune disease. We concentrated on the association with systemic lupus erythematosus (SLE), Sjögren syndrome (SS), or serological evidence of these disorders, which commonly is a source of diagnostic confusion. DESIGN Retrospective blinded serological survey. SETTING Mayo Clinic College of Medicine, Rochester, and Centre Hospitalier Régional Universitaire de Lille. METHODS Group 1 included 153 US patients with NMOSDs (78 with NMO and 75 with longitudinally extensive transverse myelitis) and 33 control subjects with SS/SLE. Group 2 included 30 French patients with SS/SLE, 14 with NMOSDs (6 with NMO, 6 with longitudinally extensive transverse myelitis, and 2 with recurrent optic neuritis), 16 without NMOSDs, and 4 with NMO without SS/SLE. RESULTS For group 1, NMO-IgG was detected in 66.7%, antinuclear antibodies in 43.8%, and Sjögren syndrome A (SSA) antibodies in 15.7% of patients with NMO and longitudinally extensive transverse myelitis. Five NMO-IgG-seropositive patients with NMOSDs had coexisting SLE, SS, or both. Antinuclear antibodies and SSA antibodies were more frequent in NMO-IgG-seropositive patients than in NMO-IgG-seronegative patients (P= .001). For group 2, NMO-IgG was detected in 5 of 14 patients (35.7%) with NMOSDs and SS/SLE and in 2 of 4 patients (50.0%) with NMO without SS/SLE (P= .59). We detected NMO-IgG only in patients with NMOSDs and not in 49 controls with SS/SLE but without optic neuritis or myelitis from the 2 cohorts (P= .01). CONCLUSION Neuromyelitis optica spectrum disorders with seropositive findings for NMO-IgG occurring with SS/SLE or non-organ-specific autoantibodies is an indication of coexisting NMO rather than a vasculopathic or other complication of SS/SLE.

Serologic diagnosis of NMO: a multicenter comparison of aquaporin-4-IgG assays.

Objectives: Neuromyelitis optica (NMO) immunoglobulin G (IgG) (aquaporin-4 [AQP4] IgG) is highly specific for NMO and related disorders, and autoantibody detection has become an essential investigation in patients with demyelinating disease. However, although different techniques are now used, no multicenter comparisons have been performed. This study compares the sensitivity and specificity of different assays, including an in-house flow cytometric assay and 2 commercial assays (ELISA and transfected cell-based assay [CBA]). Methods: Six assay methods (in-house or commercial) were performed in 2 international centers using coded serum from patients with NMO (35 patients), NMO spectrum disorders (25 patients), relapsing-remitting multiple sclerosis (39 patients), miscellaneous autoimmune diseases (25 patients), and healthy subjects (22 subjects). Results: The highest sensitivities were yielded by assays detecting IgG binding to cells expressing recombinant AQP4 with quantitative flow cytometry (77; 46 of 60) or visual observation (CBA, 73%; 44 of 60). The fluorescence immunoprecipitation assay and tissue-based immunofluorescence assay were least sensitive (48%–53%). The CBA and ELISA commercial assays (100% specific) yielded sensitivities of 68% (41 of 60) and 60% (36 of 60), respectively, and sensitivity of 72% (43 of 60) when used in combination. Conclusions: The greater sensitivity and excellent specificity of second-generation recombinant antigen-based assays for detection of NMO-IgG in a clinical setting should enable earlier diagnosis of NMO spectrum disorders and prompt initiation of disease-appropriate therapies.

CNS aquaporin-4 autoimmunity in children.

Background: In adult patients, autoantibodies targeting the water channel aquaporin-4 (AQP4) are a biomarker for a spectrum of CNS inflammatory demyelinating disorders with predilection for optic nerves and spinal cord (neuromyelitis optica [NMO]). Here we describe the neurologic, serologic, and radiographic findings associated with CNS AQP4 autoimmunity in childhood. Methods: A total of 88 consecutive seropositive children were identified through service evaluation for NMO-IgG. Sera of 75 were tested for coexisting autoantibodies. Clinical information was available for 58. Results: Forty-two patients (73%) were non-Caucasian, and 20 (34%) had African ethnicity. Median age at symptom onset was 12 years (range 4–18). Fifty-seven (98%) had attacks of either optic neuritis (n = 48; 83%) or transverse myelitis (n = 45; 78%), or both. Twenty-six (45%) had episodic cerebral symptoms (encephalopathy, ophthalmoparesis, ataxia, seizures, intractable vomiting, or hiccups). Thirty-eight (68%) had brain MRI abnormalities, predominantly involving periventricular areas (in descending order of frequency): the medulla, supratentorial and infratentorial white matter, midbrain, cerebellum, thalamus, and hypothalamus. Additional autoantibodies were detected in 57 of 75 patients (76%), and 16 of 38 (42%) had a coexisting autoimmune disorder recorded (systemic lupus erythematosus, Sjögren syndrome, juvenile rheumatoid arthritis, Graves disease). Attacks were recurrent in 54 patients (93%; median follow-up, 12 months). Forty-three of 48 patients (90%) had residual disability: 26 (54%) visual impairment and 21 (44%) motor deficits (median Expanded Disability Status Scale 4.0 at 12 months). Conclusions: Aquaporin-4 autoimmunity is a distinctive recurrent and widespread inflammatory CNS disease in children.

Aquaporin-4-binding autoantibodies in patients with neuromyelitis optica impair glutamate transport by down-regulating EAAT2.

Neuromyelitis optica (NMO)-immunoglobulin G (IgG) is a clinically validated serum biomarker that distinguishes relapsing central nervous system (CNS) inflammatory demyelinating disorders related to NMO from multiple sclerosis. This autoantibody targets astrocytic aquaporin-4 (AQP4) water channels. Clinical, radiological, and immunopathological data suggest that NMO-IgG might be pathogenic. Characteristic CNS lesions exhibit selective depletion of AQP4, with and without associated myelin loss; focal vasculocentric deposits of IgG, IgM, and complement; prominent edema; and inflammation. The effect of NMO-IgG on astrocytes has not been studied. In this study, we demonstrate that exposure to NMO patient serum and active complement compromises the membrane integrity of CNS-derived astrocytes. Without complement, astrocytic membranes remain intact, but AQP4 is endocytosed with concomitant loss of Na+-dependent glutamate transport and loss of the excitatory amino acid transporter 2 (EAAT2) . Our data suggest that EAAT2 and AQP4 exist in astrocytic membranes as a macromolecular complex. Transport-competent EAAT2 protein is up-regulated in differentiating astrocyte progenitors and in nonneural cells expressing AQP4 transgenically. Marked reduction of EAAT2 in AQP4-deficient regions of NMO patient spinal cord lesions supports our immunocytochemical and immunoprecipitation data. Thus, binding of NMO-IgG to astrocytic AQP4 initiates several potentially neuropathogenic mechanisms: complement activation, AQP4 and EAAT2 down-regulation, and disruption of glutamate homeostasis.

Paraneoplastic antibodies coexist and predict cancer, not neurological syndrome

We investigated coexisting autoantibodies in sera of 553 patients with a neurological presentation and one or more paraneoplastic neuronal nuclear or cytoplasmic autoantibodies: antineuronal nuclear autoantibody type 1 (ANNA‐1), ANNA‐2, ANNA‐3; Purkinje cell cytoplasmic autoantibody type 1 (PCA‐1), PCA‐2; and CRMP‐5–immunoglobulin G or amphiphysin–immunoglobulin G. Except for PCA‐1, which occurred alone, 31% of sera had more than one of these autoantibodies. In addition, 25% of sera had neuronal calcium channel (P/Q‐type or N‐type), potassium channel, ganglionic acetylcholine receptor, muscle acetylcholine receptor, or striational antibodies. The autoantibody profiles observed in patients with paraneoplastic disorders imply the targeting of multiple onconeural antigens and predict the patients neoplasm, but not a specific neurological syndrome. Ann Neurol 2004

Clinical spectrum of voltage-gated potassium channel autoimmunity

Objective: To document neurologic, oncologic, and serologic associations of patients in whom voltage-gated potassium channel (VGKC) autoantibodies were detected in the course of serologic evaluation for neuronal, glial, and muscle autoantibodies. Methods: Indirect immunofluorescence screening of sera from 130,000 patients performed on a service basis for markers of paraneoplastic neurologic autoimmunity identified 80 patients whose IgG bound to the synapse-rich molecular layer of mouse cerebellar cortex in a pattern consistent with VGKC immunoreactivity. Antibody specificity was confirmed in all cases by immunoprecipitation of detergent-solubilized brain synaptic proteins complexed with 125I-alpha-dendrotoxin. Results: Clinical information was available for 72 patients: 51% women, median age at symptom onset 65 years, and median follow-up period 14 months. Neurologic manifestations were acute to subacute in onset in 71% and multifocal in 46%; 71% had cognitive impairment, 58% seizures, 33% dysautonomia, 29% myoclonus, 26% dyssomnia, 25% peripheral nerve dysfunction, 21% extrapyramidal dysfunction, and 19% brainstem/cranial nerve dysfunction. Creutzfeldt-Jakob disease was a common misdiagnosis (14%). Neoplasms encountered (confirmed histologically in 33%) included 18 carcinomas, 5 adenomas, 1 thymoma, and 3 hematologic malignancies. Hyponatremia was documented in 36%, other organ-specific autoantibodies in 49%, and a co-existing autoimmune disorder in 33% (including thyroiditis 21%, type 1 diabetes mellitus 11%). Benefit was reported for 34 of 38 patients (89%) receiving immunotherapy and was marked in 50%. Conclusions: The spectrum of neurologic manifestations and neoplasms associated with voltage-gated potassium channel (VGKC) autoimmunity is broader than previously recognized. Evaluation for VGKC antibodies is recommended in the comprehensive autoimmune serologic testing of subacute idiopathic neurologic disorders.