24-19: Neuromyelitis Optica

This disorder is characterized by optic neuritis and acute myelitis with MRI changes that extend over at least three segments of the spinal cord. An isolated myelitis or optic neuritis may also occur. Previously known as Devic disease and once regarded as a variant of multiple sclerosis, neuromyelitis optica is associated with a specific antibody marker (NMO-IgG) targeting the water channel aquaporin-4 in 80% of cases, and with antibodies to myelin oligodendrocyte glycoprotein (MOG-IgG) in approximately 33% of NMO-IgG seronegative patients. MRI of the brain typically does not show widespread white matter involvement, but such changes do not exclude the diagnosis. Treatment is by long-term immunosuppression. Eculizumab is a complement inhibitor that reduced the annual relapse rate from 35% to 2% compared to placebo and is the only approved therapy for NMO-IgG positive cases. Use of eculizumab requires prior immunization against meningococcus. Inebilizumab, a humanized anti-CD19 antibody that depletes B cells, also reduced relapse rate compared to placebo in a randomized trial and was approved by the FDA in June. Off-label therapy is with rituximab (two 1-g intravenous infusions spaced by 2 weeks, or four weekly infusions of 375 mg/m²; re-dosing may occur every 6 months or when CD19/20-positive or CD27-positive lymphocytes become detectable), mycophenolate mofetil (500–1500 mg orally twice daily, titrated until the absolute lymphocyte count falls below 1500/mcL), or azathioprine (2.5–3 mg/kg orally). Acute relapses are treated with corticosteroids at doses similar to those outlined for multiple sclerosis and with plasma exchange for severe relapses unresponsive to corticosteroids.