A stroke that occurs during sleep, commonly called a “wake-up stroke,” presents a unique challenge for both patients and medical professionals. While these events are not technically different from strokes that happen during the day, the unknown timing of their onset significantly complicates treatment decisions. Wake-up strokes account for approximately one in five cases, or around 20% of all acute ischemic strokes. Recognizing the signs immediately upon waking is the most important step toward receiving medical care.
Symptoms Noticed Upon Waking
The symptoms of a sleep-related stroke are the same as any stroke, but they are only noticed upon waking. Recognizing these sudden neurological deficits is paramount and can often be done using the acronym F.A.S.T.
The “F” stands for Face drooping; ask the person to smile and check if one side of the face appears numb or droops. The “A” is for Arm weakness, assessed by asking the person to raise both arms; if one arm drifts downward or is too weak to lift, it signals a problem. “S” is for Speech difficulty, which can manifest as slurred speech, an inability to speak, or difficulty understanding a simple sentence.
Other symptoms apparent upon waking include sudden trouble seeing in one or both eyes, or a sudden loss of coordination or balance. A person might also experience sudden confusion, severe dizziness, or a sudden, severe headache with no known cause. Recognizing these symptoms and acting quickly—the “T” in F.A.S.T.—provides the best chance for a positive outcome.
Why Timing Matters for Treatment
The primary obstacle in treating a wake-up stroke is the unknown time of symptom onset. For ischemic strokes, caused by a blood clot blocking an artery in the brain, the most effective treatment is an intravenous clot-busting drug, such as tissue plasminogen activator (tPA). This medication is typically approved for administration only within a narrow window, ideally within 3 to 4.5 hours of symptom onset.
Because the onset time is unknown, medical teams must assume the stroke began when the patient was last known to be symptom-free, usually when they went to sleep. This assumption often places the patient outside the standard 4.5-hour treatment window for tPA, as they may have been asleep for six or more hours. Administering tPA beyond this timeframe significantly increases the risk of dangerous side effects, such as bleeding into the brain, often outweighing the potential benefit.
This uncertainty necessitates a different approach to determine eligibility. Newer evidence suggests that patients with unknown-onset strokes may still benefit from thrombolysis, provided they meet criteria determined by advanced imaging. The goal is to identify patients who may have suffered the stroke only shortly before waking up.
Urgent Medical Evaluation
Immediate action is the most important step for anyone who recognizes stroke symptoms upon waking; the first priority must be calling emergency services (9-1-1). Do not attempt to drive the person to the hospital, as emergency medical personnel can begin assessment and treatment en route. Once at the hospital, evaluation focuses on determining the stroke’s age to assess treatment eligibility.
For wake-up strokes, doctors use advanced neuroimaging to estimate the time of onset and assess salvageable brain tissue. A Magnetic Resonance Imaging (MRI) scan is a valuable tool, utilizing two sequences: Diffusion-Weighted Imaging (DWI) and Fluid-Attenuated Inversion Recovery (FLAIR). DWI shows areas of acute, irreversible damage very early on, while FLAIR changes typically appear later, several hours after the stroke began.
A finding of a “DWI-FLAIR mismatch”—where the DWI shows a lesion but the FLAIR sequence does not—strongly suggests the stroke is recent, likely within the last 4.5 to 6 hours. This visual confirmation of a short duration may qualify the patient for intravenous thrombolysis, despite the unknown exact time of onset. Other imaging techniques, like CT or MRI perfusion scans, help identify brain areas that are at risk but not yet irreversibly damaged, guiding eligibility for procedures such as mechanical thrombectomy, even in an extended time window.