A “wake-up stroke” is an ischemic stroke experienced during sleep, where a person goes to bed feeling normal but awakens with symptoms. Accounting for an estimated 8% to 28% of all ischemic strokes, this type presents a significant challenge for medical professionals. The precise time the stroke began is unknown, complicating eligibility for time-sensitive treatments. Since every minute without treatment means the loss of up to two million brain cells, establishing the timing is crucial for treatment decisions.
Recognizing the Signs of a Stroke Upon Waking
The symptoms of a wake-up stroke are the same as any stroke occurring while a person is awake, and immediate recognition is the most important first step. The most common signs are summarized by the FAST acronym: Face drooping, Arm weakness, Speech difficulty, and Time to call emergency services. A person may notice one side of their face is numb or droops when smiling, or that one arm feels weak and drifts downward when attempting to raise both arms. Speech may be slurred, inappropriate, or the person may be unable to speak or understand simple sentences. While mild symptoms like numbness can be confused with sleeping awkwardly, any sudden, one-sided, or significant change should be treated as a possible stroke.
Immediate Action: The Time of Last Known Normal
Once stroke symptoms are recognized upon waking, the immediate action is to call emergency services. Time is the most important factor in stroke care, and a delay in seeking help can significantly worsen the outcome. When communicating with responders, it is vital to provide the Time of Last Known Normal (LKN). The LKN is the last moment the patient was observed to be completely without stroke symptoms and functioning at their usual baseline. For a wake-up stroke, this time is typically when the person went to sleep the night before, not the time they woke up and noticed the symptoms. This information sets the starting point for the medical team to estimate the maximum possible duration of the stroke. Accurately reporting the LKN helps doctors determine eligibility for time-sensitive treatments.
Specialized Diagnostics When Onset Time Is Unclear
When the precise time of stroke onset is unknown, medical professionals rely on advanced brain imaging to estimate the stroke’s age and determine treatment eligibility. Standard imaging, like a non-contrast Computed Tomography (CT) scan, is performed quickly to rule out a hemorrhagic stroke. However, CT often lacks detail for an ischemic stroke in the early hours. Therefore, Magnetic Resonance Imaging (MRI) is often used, specifically looking at Diffusion-Weighted Imaging (DWI) and Fluid-Attenuated Inversion Recovery (FLAIR) sequences.
DWI and FLAIR Mismatch
DWI detects signs of acute ischemia, or restricted blood flow, usually within minutes of the stroke. In contrast, the FLAIR sequence typically takes six hours or more for the affected area to show a visible signal change. The presence of a DWI-FLAIR mismatch—where the stroke is visible on DWI but not yet on FLAIR—serves as an imaging biomarker. This mismatch suggests the stroke likely occurred within the preceding 4.5 hours, identifying patients who may still be eligible for certain acute therapies.
Treatment Pathways for Wake-Up Strokes
The findings from specialized imaging directly influence the treatment pathway for a wake-up stroke patient. Traditionally, intravenous thrombolysis, using a clot-busting drug like alteplase (tPA), is restricted to patients treated within 4.5 hours of a known symptom onset. However, the DWI-FLAIR mismatch allows for the safe administration of alteplase to selected wake-up stroke patients, extending the time window for this therapy. The WAKE-UP trial demonstrated that patients with this imaging profile who received alteplase had better functional outcomes. For patients with a large vessel occlusion (LVO), which are often more severe strokes, treatment involves mechanical thrombectomy.
Mechanical Thrombectomy
Mechanical thrombectomy is a procedure that threads a catheter through the blood vessels to physically remove the clot. Advanced imaging, such as CT perfusion or MRI, identifies patients who have a large area of salvageable brain tissue, known as penumbra, even if the LKN was up to 24 hours prior. This imaging-guided approach allows for an extended time window for mechanical thrombectomy, offering a positive outcome when the stroke time is ambiguous.