BACKGROUND: Neuromyelitis optica spectrum disorders (NMOSD) are central nervous system demyelinating diseases that are distinct from multiple sclerosis. According to epidemiological studies, the incidence of NMSOD peaks in individuals aged 30-40 years. Therefore, whether the clinical manifestations and prognoses of NMOSD differ on the basis of age at onset is worthy of further investigation. METHODS: The clinical, laboratory, and imaging data of NMOSD patients admitted to Peking University Third Hospital were retrospectively analyzed. EO-NMOSD was defined early onset NMOSD (age at onset <
50 years), and LO-NMOSD was defined as late onset NMOSD (age at onset >
50 years). Differences in clinical and imaging data were compared between the two groups. RESULTS: A total of 75 patients with NMOSD were enrolled. Among them, 45 patients were age <
50 years (EO-NMOSD), and 30 patients were age ≥ 50 years (LO-NMOSD). There was no significant difference in the EDSS score between the two groups at the time of onset (p = 0.071). The median EDSS scores at the last follow-up were 2 points and 3.5 points in the EO-NMOSD and LO-NMOSD groups, respectively, and the difference was statistically significant (p = 0.001). The proportions of patients with EDSS scores ≤ 3 points and 3 <
EDSS scores ≤ 6 points were significantly different between the two groups (p = 0.023, p = 0.014), and there was no significant difference in the proportion of patients with EDSS scores greater than 6 points between the two groups (p = 1.000). Spearman correlation analysis revealed that age at onset was positively correlated with EDSS scores at onset (r = 0.284, p = 0.013) and EDSS scores at the last follow-up (r = 0.425, p = 0.000) and negatively correlated with the number of attacks (r = -0.280, p = 0.015). The proportion of AQP4-ab(+) patients with EDSS scores <
3 at onset was lower in the LO-NMOSD group than in the EO-NMOSD group (27.2 % vs. 59.5 %, p = 0.017), and the proportion of AQP4-ab(+) patients with 3 <
EDSS scores ≤ 6 was greater in the LO-NMOSD group than in the EO-NMOSD group, both at onset (72.7 % vs. 32.4 %, p = 0.003) and at the last follow-up (54.5 % vs. 24.3 %, p = 0.019). In addition, the proportion of patients with hypertension in the AQP4-ab(+) group of patients with LO-NMOSD was significantly greater than that in the AQP4-ab(+) group of patients with EO-NMOSD (5.4 % vs. 27.3 %, p = 0.043). CONCLUSION: LO-NMOSD patients, particularly those who were AQP4-ab positive, had more severe functional impairments and poorer prognoses. The number of attacks in AQP4-ab(+) patients with EO-NMOSD was greater than that in AQP4-ab(+) patients with LO-NMOSD.