Introduction

Neuromyelitis optica spectrum disorders (NMOSDs) are a group of rare, inflammatory, demyelinating diseases that affect the central nervous system. Aquaporin-4-IgG (AQP-4-IgG) is detectable in over 70% of patients and plays a critical role in diagnosis.1 According to 2015 International Panel for NMO Diagnosis (IPND) criteria, patients seronegative for AQP-4-IgG can still be diagnosed with NMOSD but must meet more stringent clinical and radiological criteria.1 A subset of this group may be positive for myelin oligodendrocyte glycoprotein antibodies (MOG-Abs).2 MOG-Ab disease encompasses a broader clinical spectrum, including isolated optic neuritis (ON, often bilateral and recurrent), isolated transverse myelitis (TM) and acute demyelinating encephalomyelitis (ADEM) (online supplementary figure 1). This, coupled with a monophasic course in half and high recovery rates without residual disability, has led many to argue MOG-Ab disease should be considered a separate entity from AQP-4-IgG NMOSD.

Previous epidemiology studies have varied in relation to case ascertainment, diagnostic criteria used, age restrictions among study populations, and reporting and testing of antibodies, making cross-comparisons difficult. Limiting studies to those using the updated 2015 IPND criteria,1 prevalence and incidence rates of NMOSD, among predominantly Caucasian populations, range from 0.7 to 1.87/100 000 and 0.3–1.2/million person-years.3–6 The epidemiology of MOG-Ab disease is largely unknown.

Given the rarity of these conditions, evolving diagnostic criteria and recent availability of accurate antibody testing, these rates likely underestimate the true prevalence and incidence. Thus, in the current study, we sought to calculate the respective prevalence and incidence of NMOSD, AQP-4-IgG-positive NMOSD and MOG-Ab disease in Oxfordshire.