AQP4 and synovial sarcoma: 616 patients with SS at Peking Union Medical College Hospital, 43 of whom developed NMOSD, with an incidence rate of 7.0%. Moreover, LETM was found in 2 of 22 SS patients, of which only 1 was positive for AQP4-IgG, while no AQP4-IgG was detected in the other 21 patients, including patients with short transverse myelitis (<3 vertebral segments).