Neuromyelitis optica (NMO) is an uncommon CNS demyelinating syndrome often mistaken for severe multiple sclerosis (MS). Several clinical, laboratory, and neuroimaging characteristics may accurately distinguish NMO from MS early in the disease course.
NMO is usually a relapsing disorder associated with early, severe, attack-related residual disability. It is associated with a highly specific antibody marker, NMO-IgG, which targets the water channel aquaporin-4. Revised NMO diagnostic criteria require optic neuritis, acute myelitis, and 2 of the following 3 characteristics: disease-onset brain magnetic resonance imaging (MRI) that is nondiagnostic for MS, contiguous spinal cord MRI lesion extending over 3 or more vertebral segments, and NMO-IgG seropositive status. Symptoms referable to central nervous system regions other than the optic nerve and spinal cord do not necessarily exclude the diagnosis of NMO, nor does the presence of brain MRI lesions. NMO-IgG has facilitated an appreciation that the spectrum of NMO is wider than previously recognized, and includes a proportion of patients with each of recurrent longitudinally extensive myelitis, recurrent isolated optic neuritis, and Japanese opticospinal MS. In contrast to typical MS, clinical experience and case series suggest that NMO requires long-term immunosuppressive therapy.
NMO can be reliably differentiated from MS at an early stage using validated diagnostic criteria. The spectrum of NMO is wider than previously appreciated. Accurate, early diagnosis is critical to facilitate initiation of immunosuppressive therapy for attack prevention.