Disease Course and Outcomes in Patients With the Limited Form of Neuromyelitis Optica Spectrum Disorders and Negative AQP4-IgG Serology at Disease Onset: A Prospective Cohort Study

BACKGROUND AND PURPOSEPatients presenting with clinical characteristics that are strongly suggestive of neuromyelitis optica spectrum disorders (NMOSD) have a high risk of developing definite NMOSD in the future. Little is known about the clinical course, treatment, and prognosis of these patients with likely NMOSD at disease onset. METHODSThis study prospectively recruited and visited 24 patients with the limited form of NMOSD (LF-NMOSD) at disease onset from November 2012 to June 2021. Their demographics, clinical course, longitudinal aquaporin-4 immunoglobulin G (AQP4-IgG) serology, MRI, therapeutic management, and outcome data were collected and analyzed. RESULTSThe onset age of the cohort was 38.1±12.0 years (mean±standard deviation). The median disease duration was 73.5 months (interquartile range=44.3-117.0 months), and the follow-up period was 54.2±23.8 months. At the end of the last visit, the final diagnosis was categorized into AQP4-IgG-seronegative NMOSD (n=16, 66.7%), AQP4-IgG-seropositive NMOSD (n=7, 29.2%), or multiple sclerosis (n=1, 4.2%). Seven of the 24 patients (29.2%) experienced conversion to AQP4-IgG seropositivity, and the interval from onset to this serological conversion was 37.9±21.9 months. Isolated/mixed area postrema syndrome (APS) was the predominant onset phenotype (37.5%). The patients with isolated/mixed APS onset showed a predilection for conversion to AQP4-IgG seropositivity. All patients experienced a multiphasic disease course, with immunosuppressive therapy reducing the incidence rates of clinical relapse and residual functional disability. CONCLUSIONSDefinite NMOSD may be preceded by LF-NMOSD, particularly isolated/mixed APS. Intensive long-term follow-up and attack-prevention immunotherapeutic management is recommended in patients with LF-NMOSD.