Questioning the existence of monophasic neuromyelitis optica spectrum disorder by defining a novel long-term relapse-free form from a large Chinese population.

Objective: To clarify the existence of monophasic neuromyelitis optica spectrum disorders (NMOSD) and to identify predictive factors of long-term relapse-free form.

Methods: We retrospectively analyzed 289 Chinese patients with NMOSD. Selected subjects were divided into three groups based on the time interval between disease onset and the first relapse, if any. Clinical and imaging data were acquired from each patient's medical record and evaluated as predictive factors for NMOSD.

Results: In total, none of the participating patients exhibited a monophasic form of NMOSD. Rather, 241 patients were selected for relapse tendency analysis; 143 (59.3%) patients relapsed within the first year, 66 (27.4%) during 1-5 years, and 32 (13.3%) beyond 5 years. Such onset symptoms as optic neuritis (ON) and non-longitudinally extensive transverse myelitis (LETM) were independent prognostic factors for a prolonged remission interval (P < 0.05). The relapse rate was bi-modal for ON patients in the first year (47.9%) and beyond 5 years (24.0%) after disease onset, respectively. However, most TM and area postrema syndrome (APS) patients experienced an attack within the first year (61.3% for TM and 76.9% for APS). A survival analysis showed that attacks with APS (P < 0.0001) and TM (P < 0.05) have a significantly higher risk of early relapse than with ON and that seropositive aquaporin-4 antibody may shorten the relapse interval for all onset symptoms (P < 0.0001).

Conclusions: Our study indicated that the monophasic form of NMOSD may not exist when a sufficient follow-up period is considered. Onset phenotypes with ON, non-APS, or non-LETM attacks had a lower risk of early relapse.