More research needed on seronegative neuromyelitis optica

The authors review the general pathophysiological mechanisms underlying neuromyelitis optica (NMO) and the epidemiological, clinical and paraclinical characteristics of seronegative NMO (NMO^neg) patients.

The hallmark of NMO, a rare inflammatory disorder of the central nervous system, is the presence of autoantibodies directed against aquaporin 4 (AQP4-IgG). Despite improvement in the techniques used to detect these antibodies, around 12 to 24% of NMO patients remain seronegative for AQP4-IgG despite a definite diagnosis of NMO.

NMO^neg patients exhibit different demographic and disease-related characteristics than seropositive patients. For example, they have a lower female-male ratio and tend to have a lower relapse rate. However, the authors say that NMO^neg patients are probably not a homogenous entity and some could suffer from either atypical acute demyelinating encephalomyelitis or multiple sclerosis.

Recent studies have found high titers of autoantibodies against myelin oligodendrocyte glycoprotein in NMO^neg patients, a key indicator that disease mechanisms might differ in NMO^pos and NMO^neg. They say this challenges the position of NMO^neg patients in the spectrum of demyelinating diseases.

They argue that a reappraisal of the NMO^neg population is needed to improve NMO care. Nonetheless, they note that treatment used for NMO^pos appears to be effective for NMO^neg. They also say that since NMO^neg patients have lower disease activity than NMO^pos patients, less aggressive therapies can be used to prevent relapses.