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🦠microbiology review

Kernig's Sign

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

Kernig's sign is a physical examination maneuver used to assess for the presence of meningeal irritation, which is a hallmark symptom of bacterial meningitis. It is one of the key diagnostic signs associated with bacterial infections of the nervous system.

5 Must Know Facts For Your Next Test

  1. Kernig's sign is elicited by passively extending the patient's leg with the knee flexed, which causes pain and resistance in the back of the thigh.
  2. The presence of Kernig's sign indicates that the meninges are inflamed, which is a hallmark of bacterial meningitis.
  3. Kernig's sign is often accompanied by other signs of meningeal irritation, such as nuchal rigidity and Brudzinski's sign.
  4. The sensitivity of Kernig's sign for diagnosing bacterial meningitis is around 50-80%, meaning it is a moderately reliable indicator of the condition.
  5. Kernig's sign is an important part of the physical examination in patients suspected of having bacterial meningitis, as it can help guide the need for immediate antibiotic and supportive treatment.

Review Questions

  • Explain the pathophysiology behind Kernig's sign and its relationship to bacterial meningitis.
    • Kernig's sign is a result of meningeal irritation, which is a common feature of bacterial meningitis. When the meninges (the membranes surrounding the brain and spinal cord) become inflamed due to a bacterial infection, they become sensitive to stretching. Passively extending the leg with the knee flexed causes tension on the meninges, eliciting pain and resistance, which is observed as Kernig's sign. This sign indicates that the patient is experiencing meningeal irritation, a hallmark symptom of bacterial meningitis that requires prompt medical attention and treatment.
  • Describe the clinical significance of Kernig's sign in the diagnosis and management of bacterial diseases of the nervous system.
    • Kernig's sign is a crucial diagnostic tool in the evaluation of patients suspected of having bacterial meningitis or other bacterial infections of the nervous system. The presence of Kernig's sign, along with other signs of meningeal irritation, helps clinicians identify the likelihood of a serious bacterial infection requiring immediate antibiotic treatment. While Kernig's sign alone is not sufficient for a definitive diagnosis, its presence, combined with the patient's symptoms and other clinical findings, can guide the need for further diagnostic tests, such as lumbar puncture, and the initiation of appropriate antimicrobial therapy. Recognizing and correctly interpreting Kernig's sign is therefore essential for the timely and effective management of bacterial diseases affecting the nervous system.
  • Analyze the limitations and diagnostic accuracy of Kernig's sign in the context of bacterial diseases of the nervous system, and discuss how it should be interpreted alongside other clinical findings.
    • Kernig's sign is a moderately sensitive but not highly specific indicator of bacterial meningitis, with a sensitivity of around 50-80%. This means that while the presence of Kernig's sign can support the diagnosis of bacterial meningitis, its absence does not rule out the condition. Other factors, such as the patient's age, immune status, and the causative pathogen, can also influence the reliability of Kernig's sign. Additionally, Kernig's sign may be positive in other conditions that cause meningeal irritation, such as viral meningitis or subarachnoid hemorrhage. Therefore, Kernig's sign should be interpreted in the context of the patient's overall clinical presentation, including other signs of meningeal irritation, neurological symptoms, and laboratory findings. A comprehensive assessment, rather than reliance on a single diagnostic test, is crucial for the accurate diagnosis and appropriate management of bacterial diseases affecting the nervous system.