Stroke for USMLE Step 2 / COMLEX-USA Level 2
Cerebral Infarction Overview
- Types:
- Ischemic Stroke: 85% of strokes. Caused by an obstruction within a blood vessel supplying blood to the brain.
- Hemorrhagic Stroke: 15% of strokes. Caused by bleeding into or around the brain.
Ischemic Stroke
- Mechanisms:
- Thrombotic Stroke: Due to atherosclerosis and other pathologic processes within the cerebral arteries.
- Embolic Stroke: Often from a cardiac source, such as atrial fibrillation or post-myocardial infarction.
- Risk Factors: Hypertension, atrial fibrillation, diabetes mellitus, smoking, hyperlipidemia, and previous stroke.
Clinical Presentation
- Symptoms:
- Sudden onset of neurologic deficits, such as weakness, numbness, aphasia, ataxia, visual loss, or severe headache.
- Use of the NIH Stroke Scale to quantify the severity of symptoms.
- FAST (Face drooping, Arm weakness, Speech difficulties, Time to call 911): Quick mnemonic for stroke identification.
Diagnosis
- Imaging:
- Non-contrast CT Head: First-line to rule out hemorrhagic stroke and visualize signs of early ischemia.
- MRI with DWI: More sensitive in detecting ischemic strokes within the first few hours after symptom onset.
- Additional Studies:
- CTA or MRA of Head & Neck, or Carotid Ultrasound: To assess for carotid stenosis as a source of emboli.
- Echocardiography: To identify cardiac sources of emboli, such as atrial thrombus.
Management
- Acute Ischemic Stroke:
- Thrombolysis: Intravenous alteplase (tPA) if administered within 4.5 hours of onset and no contraindications.
- Mechanical Thrombectomy: For patients with large artery occlusions within 6-24 hours of last known normal.
- Secondary Prevention:
- Antiplatelet Therapy: Aspirin or clopidogrel or dual antiplatelet therapy based on individual risk profiles.
- Anticoagulation: For patients with atrial fibrillation or other indications.
- Statins: High-intensity statin therapy.
- Blood Pressure Management: Tight control to reduce the risk of recurrence.
- Lifestyle Modifications: Diet, exercise, smoking cessation.
High-Yield Points for Step 2
- Time is Brain: Importance of rapid assessment and management to minimize permanent disability.
- Stroke Mimics: Recognizing conditions such as hypoglycemia, migraines, or seizures that can mimic stroke symptoms.
- Post-Stroke Care: Rehabilitation, addressing complications such as spasticity, and preventing common sequelae like deep vein thrombosis.