USMLE Guide: Neurology of Stroke

Introduction

Neurology of Stroke is a crucial topic for the United States Medical Licensing Examination (USMLE). This guide aims to provide a comprehensive overview of the essential concepts related to the neurology of stroke. It covers the definition, classification, etiology, pathophysiology, clinical presentation, diagnosis, and management of stroke.

I. Definition

A stroke, also known as a cerebrovascular accident (CVA), refers to the sudden onset of neurological deficits caused by the interruption of blood flow to the brain. It is a medical emergency and requires immediate attention.

II. Classification

1. Ischemic Stroke: Caused by a blockage or occlusion of a cerebral artery, resulting in inadequate blood supply to the brain.
2. Hemorrhagic Stroke: Caused by bleeding into the brain parenchyma or surrounding spaces due to ruptured blood vessels.

III. Etiology

1. Ischemic Stroke:
   • Thrombotic Stroke: Formation of a blood clot within a cerebral artery.
   • Embolic Stroke: Occlusion of a cerebral artery by an embolus originating from a distant source.
2. Hemorrhagic Stroke:
   • Intracerebral Hemorrhage: Bleeding within the brain due to rupture of a blood vessel.
   • Subarachnoid Hemorrhage: Bleeding in the subarachnoid space, typically caused by a ruptured cerebral aneurysm.

IV. Pathophysiology

1. Ischemic Stroke:
   • Reduced blood flow leads to cerebral hypoxia and subsequent neuronal injury.
   • Activation of inflammatory cascades, excitotoxicity, and oxidative stress contribute to further damage.
2. Hemorrhagic Stroke:
   • Blood extravasation causes direct mechanical damage and compression of adjacent brain tissue.
   • Toxic effects of blood components and subsequent inflammation worsen neuronal injury.

V. Clinical Presentation

1. Ischemic Stroke:
   • Sudden onset of focal neurological deficits corresponding to the affected cerebral artery territory.
   • Symptoms may include hemiparesis, hemisensory loss, aphasia, visual field defects, and neglect.
2. Hemorrhagic Stroke:
   • Sudden onset of severe headache often described as "the worst headache of my life."
   • Additional symptoms may include altered mental status, nausea/vomiting, focal deficits, and seizures.

VI. Diagnosis

1. History and Physical Examination:
   • Detailed assessment of neurological deficits and risk factors.
2. Imaging:
   • Non-Contrast CT scan: Differentiates between ischemic and hemorrhagic stroke.
   • MRI: Helpful in identifying the location and extent of ischemic injury.
   • CT Angiography/Magnetic Resonance Angiography: Evaluates the cerebral vasculature.
3. Laboratory Tests:
   • Complete Blood Count: Rules out thrombocytopenia or coagulopathy.
   • Coagulation Profile: Assesses clotting factors and bleeding disorders.
   • Lipid Profile: Evaluates hyperlipidemia as a risk factor.

VII. Management

1. Ischemic Stroke:
   • Thrombolytic Therapy: Administer recombinant tissue plasminogen activator (tPA) within the therapeutic window.
   • Endovascular Thrombectomy: Mechanical removal of the clot using a catheter-based approach.
   • Antiplatelet Therapy: Initiate aspirin within 24-48 hours.
2. Hemorrhagic Stroke:
   • Neurosurgical Intervention: Consider surgical evacuation for large intracerebral hemorrhages.
   • Blood Pressure Control: Maintain systolic blood pressure <140 mmHg.
   • Supportive Care: Monitor intracranial pressure, correct coagulopathy, and manage seizures.

Conclusion

Understanding the neurology of stroke is crucial for the USMLE as it helps assess a candidate's knowledge of the definition, classification, etiology, pathophysiology, clinical presentation, diagnosis, and management of stroke. This guide summarizes the key points necessary for success on the exam.