Background People with multiple sclerosis (MS) are more likely to develop stroke than those without. However, little is known about the association between neuromyelitis optica spectrum disorder (NMOSD) and the risk of stroke. We aimed to estimate the risk of stroke in patients with MS and NMOSD in South Korea.

Methods Data from the Korean National Health Insurance between January 2010 and December 2017 were analysed. A total of 1541/1687 adult patients with MS/NMOSD, who were free of stroke were included. Matched controls were selected based on age, sex and the presence of hypertension, diabetes mellitus and dyslipidaemia.

Results The risk of developing stroke was 2.78 times higher (adjusted HR (aHR), 95% CI 1.91 to 4.05) in patients with MS compared with controls matched by age, sex, hypertension, diabetes mellitus and dyslipidaemia. The risk of stroke in NMOSD was also higher than that in matched controls (aHR=1.69, 95% CI 1.10 to 2.61) and not statistically different from that of MS (p=0.216). The patients with MS had a higher risk for either of ischaemic or haemorrhagic stroke (HR=2.63 and 2.93, respectively), whereas those with NMOSD had a higher risk for ischaemic stroke (HR=1.60) with marginal statistical significance.

Conclusions The risk of stroke is increased in patients with MS and NMOSD and seemed comparable between the two conditions. This is the first study that estimates the risk of stroke in patients with MS and NMOSD within the same population.