Neuromyelitis optica spectrum disorder (NMOSD): Recent advances and insights from Taiwan

Neuromyelitis optica spectrum disorder (NMOSD), characterized by the pathognomonic aquaporin-4 immunoglobulin G (AQP4-IgG) antibody, is a relapsing autoimmune disease distinct from multiple sclerosis. There are six core clinical features include optic neuritis, longitudinally extensive transverse myelitis (LETM), area postrema syndrome, diencephalic clinical syndrome, acute brainstem syndrome and symptomatic cerebral syndrome. Taiwanese studies showed that patients share similar characteristics with Asian and Caucasian populations, including female predominance, onset age in the late thirties, and a median annual relapse rate of 0.5. Notably, Taiwanese patients had high prevalence of preceding hepatitis B virus (HBV) infection, and the risk of HBV reactivation requires careful management during methylprednisolone pulse therapy, prolonged steroid use or biologic treatment. Acute relapses are managed with high-dose intravenous methylprednisolone, often combined with plasma exchange in severe attacks (EDSS ≥4 or visual acuity <0.1). For maintenance therapy, azathioprine or mycophenolate mofetil, either as monotherapy or combined with corticosteroid, is recommended. More recently, monoclonal antibodies including inebilizumab and satralizumab have been reimbursed in Taiwan under strict National Health Insurance regulations, restricted to AQP4-IgG-seropositive patients with high disease severity refractory to oral immunotherapy. This review provides an updated overview of NMOSD diagnosis and treatment, with emphasis on the characteristics of Taiwanese patients.