Seroprevalence of NMO-IgG Antibody in Neuromyelitis optica (NMO) and Its Specificity in Differentiating NMO from Other Demyelinating Diseases with Overlap Symptoms: An Iranian Experience

Neuromyelitis optica is an inflammatory demyelinating disease (IDD) of the CNS, which mainly affects optic nerve and spinal cord. Autoantibodies against aquaporin-4 also known as NMO-IgG have been implicated in the pathogenesis of NMO. We evaluated the sensitivity and specificity of NMO-IgG assay for diagnosing NMO patients and differentiating them from MS patients and those with undifferentiated IDD with overlap symptoms.Eligibility of patients with demyelinating disorders was evaluated based on physical examination, laboratory and imaging studies. Thirty four definite NMO patients (disregarding NMO-IgG status), 34 multiple sclerosis (MS) patients with a history of optic neuritis (ON) or myelitis that were matched for age and disease activity and 44 patients with ON or myelitis attacks fulfilling neither criteria of MS or NMO (NMO spectrum) were selected as undifferentiated group. NMO-IgG was measured in the serum of the included patients by cell-based indirect immunofluorescence assay (IFA).NMO antibody was positive in 11 (32.3%), and 4 (9.09%) patients in NMO and undifferentiated groups, but was undetctable in MS patients. NMO antibody was 32% (95%Cl: 19-49%) sensitive in detecting NMO patients. Its specificity in differentiating NMO from MS subjects was 100 %(95% Cl: 90-!00%). NMO antibody was 95% (95% Cl: 0.88-0.98) specific in differentiating NMOs from other demyelinating diseases.Our results showed that although NMO antibody is highly specific for NMO, current method of measuring it with cell-based IFA is not highly sensitive for diagnosing NMO patients.