USMLE Guide: Stroke

Introduction

This guide provides an overview of stroke, a frequently tested topic on the United States Medical Licensing Examination (USMLE). It aims to help medical students and professionals understand the key concepts, pathophysiology, clinical features, diagnostic methods, and management of stroke.

Table of Contents

1. Definition and Types of Stroke
2. Risk Factors
3. Pathophysiology
4. Clinical Presentation
5. Diagnostic Methods
6. Management
7. Complications and Prognosis
8. Conclusion

1. Definition and Types of Stroke

• Stroke refers to the sudden onset of focal neurological deficits caused by a disruption in blood supply to the brain.
• There are two main types of stroke:
  • Ischemic Stroke: Caused by a blockage or reduced blood flow to a specific brain region.
  • Hemorrhagic Stroke: Caused by bleeding into the brain tissue or surrounding spaces.

2. Risk Factors

• Modifiable risk factors:
  • Hypertension
  • Diabetes mellitus
  • Smoking
  • Hyperlipidemia
  • Obesity
  • Sedentary lifestyle
• Non-modifiable risk factors:
  • Age (>55 years)
  • Gender (male > female)
  • Family history of stroke
  • Ethnicity (African Americans have a higher risk)

3. Pathophysiology

• Ischemic Stroke:
  • Thrombotic stroke: Formation of a blood clot within a cerebral artery.
  • Embolic stroke: Occlusion of a cerebral artery by an embolus originating elsewhere in the body.
• Hemorrhagic Stroke:
  • Intracerebral hemorrhage: Bleeding into the brain tissue due to rupture of a blood vessel.
  • Subarachnoid hemorrhage: Bleeding into the subarachnoid space surrounding the brain due to a ruptured cerebral aneurysm.

4. Clinical Presentation

• Common symptoms of stroke include:
  • Sudden-onset focal weakness or paralysis
  • Facial droop
  • Difficulty speaking or understanding speech
  • Visual disturbances
  • Severe headache (in case of hemorrhagic stroke)
• Symptoms depend on the affected brain region.

5. Diagnostic Methods

• Non-contrast CT scan: Preferred initial imaging study to differentiate ischemic stroke from hemorrhagic stroke.
• MRI: More sensitive than CT scan in detecting ischemic stroke and can identify the age of the infarct.
• CT angiography or MRA: To identify vascular abnormalities or stenosis.
• Blood tests: Assess for risk factors and potential causes.

6. Management

• Acute management:
  • Ischemic stroke:
    • IV thrombolytic therapy (alteplase) within 4.5 hours of symptom onset (if eligible).
    • Mechanical thrombectomy for large vessel occlusion (within 24 hours).
  • Hemorrhagic stroke:
    • Supportive care, including blood pressure control and management of intracranial pressure.
• Secondary prevention:
  • antiplatelet agents (aspirin, clopidogrel) for ischemic stroke.
  • Anticoagulation (warfarin, NOACs) for cardioembolic stroke.
  • Blood pressure control, statin therapy, lifestyle modifications.

7. Complications and Prognosis

• Complications:
  • Hemiparesis or hemiplegia
  • Aphasia
  • Dysphagia
  • Seizures
  • Cognitive impairment
• Prognosis is worse for hemorrhagic stroke compared to ischemic stroke.
• Rehabilitation and supportive care play a crucial role in improving outcomes.

8. Conclusion

Stroke is a significant cause of morbidity and mortality worldwide. Understanding the different types, risk factors, pathophysiology, clinical presentation, diagnostic methods, and management options is essential for medical professionals. By reviewing this guide, you will be better prepared to answer stroke-related questions on the USMLE and provide optimal care for stroke patients in your future medical practice.

Note: This guide is for educational purposes only and should not replace professional medical advice or clinical judgment.