We determined the presence of aquaporin-4 (AQP4) antibodies by indirect immunofluorescence in human AQP4-transfected cells, and evaluated the diagnostic and prognostic relevance of AQP4 antibodies in 210 Chinese patients with neuromyelitis optica (NMO), high-risk NMO (HR-NMO), classic multiple sclerosis (MS), and other neurologic diseases. Patients were enrolled from The General Hospital of the Chinese People's Liberation Army and followed-up for a median of 2 years. The patients with HR-NMO had optico-spinal MS (OSMS; n=3), longitudinally extensive transverse myelitis (TM) (n=35), recurrent optic neuritis (ON) (n=2), ON with Sjögren's syndrome (n=1) and TM positive for Sjögren-A(SSA) antibody (n=1). The sensitivity and specificity of AQP4 antibodies in NMO were 70.9% and 91%, respectively. The median AQP4 antibody titer was significantly higher in patients with NMO (1:320) than in those with HR-NMO (1:100) and MS (1:50). Relapse of ON or TM was more likely in patients with AQP4 seropositive, than AQP4 seronegative, HR-NMO. Among AQP4 seropositive patients, 66.7% (36/55) had severe ON, 75.9% (41/55) had TM, and 55.6% (30/55) had spinal cord lesions longer than three segments, and there were relapses in eight of 55 patients with ON (14.8%) and 19 of 55 patients with TM (35.2%) during the 2-year follow-up. In conclusion, our study reveals that AQP4 antibody is a sensitive and specific biomarker for discrimination of NMO, classic MS, and other neurological diseases, and is particularly useful for the diagnosis of HR-NMO. AQP4 antibody-positive patients showed higher frequencies of relapse of ON or TM compared with AQP4 antibody-negative patients.
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