A 58-year-old man with hypertension and diabetes presents to the emergency department with acute onset of left-sided weakness and speech difficulty for the past 2 hours. Non-contrast CT head is normal. What is the investigation of choice to confirm acute ischemic stroke and guide thrombolytic therapy?

Explanation

## Investigation of Choice: DWI-MRI for Acute Ischemic Stroke ### Why DWI-MRI is the Gold Standard **Key Point:** Diffusion-weighted imaging (DWI) MRI is the most sensitive imaging modality for detecting acute ischemic stroke, with sensitivity >90% within minutes of symptom onset, whereas conventional CT or MRI may appear normal in the hyperacute phase. **High-Yield:** DWI-MRI detects restricted water diffusion in ischemic tissue (cytotoxic edema) within **minutes** of stroke onset. This makes it the gold standard for: - Confirming acute ischemia when CT is normal - Distinguishing acute from chronic infarcts - Identifying small brainstem or cerebellar infarcts missed on CT - Guiding thrombolytic therapy decisions ### Clinical Context in This Case The patient has: - Classic acute stroke presentation (2 hours = hyperacute phase) - Normal non-contrast CT (rules out hemorrhage, permitting thrombolysis consideration) - Need for **definitive confirmation** of ischemia before administering IV alteplase or mechanical thrombectomy DWI-MRI will show hyperintense signal in the distribution of the occluded vessel, confirming acute ischemia and justifying urgent reperfusion therapy. ### Comparison with Other Modalities | Investigation | Sensitivity in Hyperacute Phase | Clinical Role | Limitations | |---|---|---|---| | **DWI-MRI** | >90% within minutes | Gold standard for acute ischemia | Requires MRI availability; contraindicated with certain implants | | CT Angiography (CTA) | N/A for ischemia detection | Shows vessel occlusion; guides thrombectomy | Does not confirm tissue-level ischemia | | Transcranial Doppler | N/A for diagnosis | Assesses flow velocity; research use | Operator-dependent; no tissue confirmation | | EEG | N/A | Detects seizures (post-stroke complication) | Not diagnostic for acute ischemia | **Clinical Pearl:** In centers with rapid MRI access, DWI-MRI is preferred over CT in the hyperacute window. However, if MRI is unavailable or contraindicated, non-contrast CT + CTA is acceptable to rule out hemorrhage and identify large vessel occlusion. ### Thrombolytic Window Consideration The patient is within the **4.5-hour IV thrombolysis window** and **24-hour mechanical thrombectomy window** (if large vessel occlusion). DWI-MRI confirmation accelerates decision-making and reduces risk of treating stroke mimics (e.g., Todd's paralysis, hemiplegic migraine). [cite:Harrison 21e Ch 296]