Wake-up stroke and unknown-onset stroke; occurrence and characteristics from the nationwide Norwegian Stroke Register.

Introduction: Population-based knowledge of the characteristics of wake-up stroke and unknown-onset stroke is limited. We compared occurrence and characteristics of ischaemic and haemorrhagic wake-up stroke, unknown-onset stroke and known-onset stroke in a nationwide register-based study. Patients and methods: We included patients registered in the Norwegian Stroke Register from 2012 through 2019. Age, sex, risk factors, clinical characteristics, acute stroke treatment and discharge destination were compared according to stroke type and time of onset. Results: Of the 60,320 patients included, 11,451 (19%) had wake-up stroke, 11,098 (18.4%) had unknown time of onset and 37,771 (62.6%) had known symptom onset. The proportion of haemorrhagic stroke was lower among wake-up stroke patients (1107/11,451, 9.7%, 95% CI: 9.1-10.2) than for known-onset stroke (5230/37,771, 13.8%, 95% CI: 13.5-14.2) and for unknown-onset stroke (1850/11,098, 16.7%, 95% CI: 16.0-17.4). Mild stroke (NIHSS <5) was more frequent in ischaemic wake-up stroke (5364/8308, 64.6%, 95% CI: 63.5-65.5) than in known-onset (16,417/26,746, 61.4%, 95% CI: 60.8-62.0) and unknown-onset stroke (3242/5853, 55.4%, 95% CI: 54.1-56.7), while baseline characteristics were otherwise similar to known-onset stroke. Unknown-onset stroke patients were more often female, lived alone and had more severe strokes compared to wake-up stroke and known-onset stroke patients. Unknown-onset stroke patients were more often in need of community-based health care on discharge and had a higher in-hospital mortality. Discussion and conclusions: Ischaemic wake-up strokes shared baseline characteristics with known-onset strokes, but tended to be milder. Ischaemic unknown-onset stroke patients differed significantly from wake-up stroke, emphasising the importance of considering them as separate entities.