Stroke for USMLE Step 1 / COMLEX-USA Level 1
Cerebral Infarction Overview
- Definition: Occurs when there is ischemia to a part of the brain, leading to a focal neurological deficit that lasts beyond 24 hours.
- Types:
- Ischemic Stroke: Most common type, accounting for about 85% of all strokes. It occurs when a blood clot blocks or narrows an artery leading to the brain.
- Hemorrhagic Stroke: Caused by bleeding into or around the brain, accounts for 15% of strokes.
Stroke Syndromes
See: Stroke Syndromes
Pathophysiology
- Mechanisms of Ischemia:
- Thrombotic Stroke: Formation of a clot within a cerebral artery, often at a site of atherosclerosis.
- Embolic Stroke: A clot forms elsewhere in the body (commonly in the heart) and travels to the brain.
- Penumbra: The ischemic but potentially salvageable area surrounding the core of the infarct.
- Cellular Effects: Lack of oxygen and nutrients leads to cell death primarily through necrosis and apoptosis in the core area.
Risk Factors
- Modifiable: Hypertension, diabetes, smoking, dyslipidemia, atrial fibrillation, and obesity.
- Non-modifiable: Age, gender, race, family history, and genetic predisposition.
Clinical Presentation
- Symptoms: Depend on the area of the brain affected but commonly include unilateral weakness, speech disturbance, confusion, visual changes, and severe headache (more common in hemorrhagic stroke).
- FAST (Face drooping, Arm weakness, Speech difficulties, Time to call emergency services): Acronym used to help identify stroke symptoms quickly.
Diagnosis
- Imaging:
- CT Scan: First-line imaging modality to distinguish between ischemic and hemorrhagic stroke.
- MRI: More sensitive for detecting early ischemic changes and small infarcts.
Management
- Acute Management of Ischemic Stroke:
- Reperfusion Therapy: Intravenous thrombolysis (e.g., tPA) within a 4.5-hour window from symptom onset.
- Mechanical Thrombectomy: For large vessel occlusions, can be considered up to 24 hours from onset in certain patients.
- Preventive Treatment:
- Antiplatelet Drugs: Aspirin, clopidogrel for long-term secondary prevention.
- Control of Risk Factors: Management of hypertension, diabetes, cholesterol, and lifestyle modifications.
High-Yield Points for Step 1
- Pathophysiology of Stroke: Understanding of how thrombotic and embolic mechanisms lead to brain tissue damage.
- Identification and Management of Risk Factors: Knowledge of how to modify risk factors is crucial for prevention.
- Basics of Acute Stroke Management: Familiarity with the timing and indications for thrombolytic therapy.