Longitudinally Extensive Transverse Myelitis With and Without Aquaporin 4 Antibodies

Abstract

Until the discovery of aquaporin 4 antibodies (AQP4-Ab) in 2005,¹ neuromyelitis optica (NMO) was defined clinically as the coexistence of inflammatory myelitis and optic neuritis without symptomatic disease outside of these regions.² The high specificity of AQP4-Ab^3-5 has enabled broadening of the clinical phenotype of NMO; it has become clear that many patients have limited forms of disease such as monophasic or recurrent longitudinally extensive transverse myelitis (LETM) or less commonly bilateral or recurrent optic neuritis or brain disease, together encompassed by the term NMO spectrum disorders (NMOSD).⁶ We recently found that 47% of AQP4-Ab–positive patients had limited disease, most commonly monophasic or recurrent LETM.⁷ The NMO diagnostic criteria⁸ do not currently include such patients but most specialists agree that they should be treated the same as those with the full NMO phenotype, with early and aggressive immunosuppression. The diagnostic criteria need updating to reflect the expanding spectrum of NMO with AQP4-Ab. On the other hand, it is less clear how to classify and treat patients with NMO/NMOSD without AQP4-Ab. This is important for the correct definition of patients in clinical studies, which will influence outcome predictions and patient management.