A 70-year-old man presents with sudden onset aphasia and right hemiplegia at 9 AM. Last seen well at 10 PM the previous night. Non-contrast CT brain shows no haemorrhage. MRI DWI shows early restricted diffusion in the left MCA territory with FLAIR mismatch (DWI lesion without FLAIR change). What does this finding suggest and what is its therapeutic implication?
- A The stroke is beyond 4.5 hours; no thrombolysis possible
- B FLAIR mismatch indicates haemorrhagic transformation; anticoagulation required
- C FLAIR mismatch suggests stroke occurred within 4.5 hours; thrombolysis may be safely administered ✓
- D MRI DWI lesion without FLAIR change indicates a transient ischaemic attack
Correct answer: C. FLAIR mismatch suggests stroke occurred within 4.5 hours; thrombolysis may be safely administered
Explanation
DWI-FLAIR mismatch refers to restricted diffusion on DWI in the absence of matching FLAIR signal change, which occurs in acute stroke within approximately 4.5 hours of onset, since FLAIR takes longer to become positive. In patients with unknown onset ('wake-up stroke' or last known well >4.5 h), DWI-FLAIR mismatch is used as a surrogate to identify those who can still benefit from IV alteplase. This was validated in the WAKE-UP trial (2018), which showed improved outcomes with MRI-guided thrombolysis in wake-up strokes using this criterion.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.