What is the difference between Brudzinski's sign and Kernig's sign?

From the Guidelines

Brudzinski and Kernig signs are two distinct clinical tests used to detect meningeal irritation, differing in their execution and patient positioning, with the Brudzinski sign involving neck flexion and the Kernig sign involving knee extension in a specific patient position. The key difference between these signs lies in how they are performed and the patient's response to the maneuver. According to the escmid guideline on the diagnosis and treatment of acute bacterial meningitis 1, these clinical findings have low diagnostic accuracy for predicting cerebrospinal fluid (CSF) pleocytosis, with sensitivities of 31% for neck stiffness, 9% for Brudzinski sign, and 11% for Kernig sign.

Clinical Application

• The Brudzinski sign is performed by flexing the patient's neck while they are in a supine position, and it is considered positive if this movement causes involuntary flexion of the hips and knees.
• The Kernig sign, on the other hand, is performed with the patient lying supine and the hip and knee flexed at 90 degrees; the examiner then attempts to extend the knee, and a positive sign is indicated by pain or resistance upon knee extension.
• Both signs are used to aid in the diagnosis of conditions such as meningitis, subarachnoid hemorrhage, or other causes of meningeal irritation, but their low sensitivity means that their absence cannot be used to rule out these conditions, as highlighted in the guideline 1.

Diagnostic Considerations

• Given the low diagnostic accuracy of these signs, they should be used in conjunction with other clinical findings, such as fever, headache, and altered mental status, to guide further investigation.
• Positive findings on either the Brudzinski or Kernig sign should prompt further diagnostic workup, potentially including imaging studies and lumbar puncture, especially in the presence of other suggestive symptoms.
• It is crucial to perform these tests gently to avoid causing unnecessary pain to the patient, as emphasized by the need for a thorough yet compassionate clinical assessment.

From the Research

Difference between Brudzinski and Kernig signs

• Brudzinski's sign is described as the "nape of the neck" sign, which is the best known of several signs of meningitis described by Brudzinski 2.
• Kernig's sign, on the other hand, is described in physical diagnosis texts, but the test for Kernig's sign as currently performed differs from Kernig's original description 2.
• Both signs are used to aid in the diagnosis of meningitis, but their diagnostic accuracy has been questioned in several studies 3, 4.
• The sensitivity of Kernig's sign and Brudzinski's sign has been reported to be low, at 5% in one study 3.
• Nuchal rigidity, another classic meningeal sign, has been found to have some diagnostic value in patients with severe meningeal inflammation, but not in the broad spectrum of adults with suspected meningitis 3.
• The use of these clinical signs in combination with other features in the history and examination can contribute to a comprehensive clinical assessment and increase the likelihood of a diagnosis of meningitis 4.

Diagnostic Accuracy

• The diagnostic accuracy of Kernig's sign, Brudzinski's sign, and nuchal rigidity has been found to be limited in adults with suspected meningitis 3.
• The likelihood ratio for a positive test result for Kernig's sign and Brudzinski's sign has been reported to be 0.97, indicating that these signs do not accurately discriminate between patients with meningitis and patients without meningitis 3.
• The diagnostic accuracy of these signs may be improved when used in combination with other clinical features and laboratory tests 4.