Neuromyelitis optica spectrum disorder (NMOSD) is a rare, chronic, immune-mediated disorder of the central nervous system. Disability accrual in NMOSD is primarily associated with acute relapses that have poor recovery, rather than progression or neurodegeneration. According to the International Consensus Diagnostic Criteria for Neuromyelitis Optica Spectrum Disorders, NMOSD patients can be diagnosed based on a clinical event with positive AQP4-IgG. Additionally, patients with unknown or negative AQP4-IgG can be diagnosed using stricter criteria, which include the presence of at least one core clinical event and additional Magnetic Resonance Imaging (MRI) requirements (Wingerchuk et al., 2015). This approach allows for the diagnosis and proper treatment of patients with a typical clinical picture consistent with NMOSD, without being limited by access to AQP4-IgG testing, which may be unavailable in some regions due to economic or technical issues. In recent years, AQP4-IgG tests have become more widely available globally, leading to the identification of a distinct group of AQP4-IgG seronegative patients.

Global NMOSD registries indicate that AQP4-IgG-positive disease is more prevalent among individuals of Asian and African descent. However, there is a significant lack of information regarding AQP4-IgG-negative cases (Hor et al., 2020). Furthermore, available evidence suggests that AQP4-IgG-positive NMOSD is linked to a more severe course and more autoimmune comorbidities, while seronegative cases tend to show milder presentations and better outcomes (Cakan et al., 2025 Jun 15). Recognizing the clinical and prognostic differences between AQP4-IgG-positive and AQP4-IgG-negative cases is essential to improve diagnostic accuracy, guide individualized treatment decisions, and anticipate disease trajectories.

Although epidemiological studies on NMOSD have been conducted in Latin America, the epidemiology of the disease in the region remains poorly characterized, particularly in terms of clinical phenotypes, serostatus distribution, and ethnic variations (Alvarenga et al., 2017; Rivera et al., 2021). Despite international efforts to characterize NMOSD, Latin American populations remain underrepresented in epidemiological and clinical studies. This gap limits our understanding of regional disease behavior and impedes the development of context-specific healthcare strategies. This gap in knowledge highlights the need for an updated multicenter registry of Latin American NMOSD patients, including both AQP4-IgG-positive and AQP4-IgG-negative individuals, to identify demographic patterns, risk factors, and potential therapeutic implications.