AQP4 and transverse myelitis: Patients with negative AQP4-Abs onset and clinical manifestations that do not meet the diagnostic criteria, including isolated area postrema syndrome (APS), isolated optic neuritis, isolated longitudinally extensive transverse myelitis, simultaneous short-segment transverse myelitis, and other core clinical manifestations, are diagnosed with the inaugural limited form of NMOSD (LF-NMOSD), which precedes future definite NMOSD (15, 17).