4,447 patients suspected of having NMOSD with acute neurological episodes and the presence of SS-related symptoms, and 1,651 were positive for serum AQP4-IgG. Compared to AQP4-IgG-negative patients, the prevalence of SS was much higher among AQP4-IgG-positive. Additionally, comorbid SS was more prevalent in females, and it had a higher relapse frequency among AQP4-IgG-positive patients. Here, AQP4 is linked to synovial sarcoma.