Nationwide epidemiological study of neuromyelitis optica in Japan

Neuromyelitis optica (NMO) is characterised by severe optic neuritis and transverse myelitis. In contrast to multiple sclerosis (MS), there have been few large-scale epidemiological surveys of NMO. The worldwide prevalence of NMO is estimated to be 1 in 100 000. NMO may be more prevalent in Asia, Africa and Latin America than in Europe and North America. NMO has been well recognised following the discovery of anti-aquaporin 4 (AQP4) antibody, and highly sensitive and specific cell-based assays using AQP4 antibody are widely available in Japan. Based on previous literature, we planned and performed the first-ever nationwide epidemiological study of NMO in Japan, which has a population of about 130 million. An advantage of performing a nationwide survey in Japan is that the Japanese archipelago stretches for 3500 km from north to south (45°−24° N). As the north–south gradient for the prevalence of MS is an important epidemiological finding reported in Japan and other countries, Japan is an ideal country to study potential differences in the prevalence of NMO associated with changes in latitude. We conducted a nationwide survey on NMO in clinical departments using established epidemiological methods in 20111. The survey was performed at departments of neurology, internal medicine, paediatrics, neurosurgery, orthopaedics, ophthalmology and psychiatry based on random selection using a stratified sampling method. Although the diagnostic criteria for NMO were …