What are Kernig and Brudzinski signs?

Kernig and Brudzinski Signs: Clinical Examination Maneuvers for Meningeal Irritation

Kernig and Brudzinski signs are classic physical examination findings for meningeal irritation, but they should not be relied upon for diagnosing meningitis due to their extremely poor sensitivity (5-11%), despite high specificity. 1

What These Signs Are

Kernig's Sign

• Technique: The patient's hip is flexed to 90°, then the examiner attempts to extend the knee 1
• Positive result: Pain occurs with knee extension, indicating meningeal irritation 1

Brudzinski's Sign

• Technique: The examiner flexes the patient's neck forward 1
• Positive result: This causes involuntary flexion of the patient's hips and knees 1
• Brudzinski actually described several signs of meningitis, with the "nape of the neck" sign being the best known, though he also described contralateral leg signs that are unfamiliar to most clinicians 2

Critical Clinical Limitations

These signs have extremely poor diagnostic accuracy and should never be used to rule out meningitis. 1

Poor Sensitivity

• Kernig's sign: Sensitivity of only 5-11% 1, 3, 4
• Brudzinski's sign: Sensitivity of only 5-9% 1, 3
• Neck stiffness: Sensitivity of only 31% in adults 3, 4
• In one study of 297 adults with suspected meningitis, both Kernig's and Brudzinski's signs had a sensitivity of just 5% and likelihood ratios of 0.97, meaning they did not accurately discriminate between patients with and without meningitis 5

High Specificity But Clinically Unhelpful

• While these signs can have specificity up to 95%, their extremely low sensitivity means their absence cannot exclude meningitis 1
• The UK Joint Specialist Societies explicitly recommend: "Kernig's sign and Brudzinski's sign should not be relied upon for diagnosis" (Grade 2B recommendation) 1

The Classic Triad Is Rarely Complete

• The "classic triad" of fever, neck stiffness, and altered mental status is present in only 41-51% of bacterial meningitis cases 1, 3
• This means approximately half of patients with bacterial meningitis will not have all three classic features 1

Clinical Implications for Practice

When to Suspect Meningitis

Document the presence or absence of these key features instead of relying on Kernig/Brudzinski signs 1:

• Headache
• Altered mental status
• Neck stiffness (though remember its poor sensitivity)
• Fever
• Rash (of any description)
• Seizures
• Signs of shock (hypotension, poor capillary refill time)

The Gold Standard

• Cerebrospinal fluid (CSF) examination remains the cornerstone of diagnosis, regardless of the presence or absence of classic symptoms 3
• CSF white blood cell count is the best diagnostic parameter for differentiating bacterial meningitis from other diagnoses (area under curve 0.95) 3
• Never delay lumbar puncture based on the absence of meningeal signs 1, 3

Special Populations at Risk for Atypical Presentations

• Elderly patients: More likely to have altered consciousness but less likely to have neck stiffness or fever 1
• Immunocompromised patients: May have blunted inflammatory responses 3
• Neonates: Often present with nonspecific symptoms 3

Common Pitfalls to Avoid

• Never rule out meningitis based on negative Kernig or Brudzinski signs - their sensitivity is too low 1
• Do not wait for the complete classic triad - it's present in less than half of cases 1, 3
• Individual signs like fever, headache, or neck stiffness alone are poor discriminators - combinations of symptoms are more useful 1
• Concern from the referring physician or family should always be taken seriously, even when classic signs are absent 1

When These Signs May Have Limited Value

• Jolt accentuation of headache (JAH) has shown slightly higher accuracy (0.749) compared to Kernig (0.667) and Brudzinski (0.720) signs, though all remain in the poor-to-fair range 6
• Nuchal rigidity showed diagnostic value only in patients with severe meningeal inflammation (≥1000 WBCs/mL of CSF), with 100% sensitivity in this subset 5