How do I perform and interpret the meningeal irritation signs (Kernig sign and Brudzinski sign) for meningitis?

Meningeal Signs: Performance and Interpretation

Kernig's and Brudzinski's signs should NOT be relied upon for diagnosing meningitis due to their poor sensitivity (as low as 5%), though they have high specificity (up to 95%). 1

How to Perform the Signs

Kernig's Sign

• Position the patient supine
• Flex the hip to 90 degrees
• Attempt to extend the knee while maintaining hip flexion
• Positive: Pain or resistance when extending the knee beyond 135 degrees

Brudzinski's Sign

• Position the patient supine
• Place your hand behind the patient's head
• Passively flex the neck, bringing the chin toward the chest
• Positive: Involuntary flexion of the hips and knees occurs

Nuchal Rigidity (Neck Stiffness)

• Attempt passive flexion of the patient's neck
• Positive: Resistance or inability to touch chin to chest

Critical Interpretation

The absence of these signs does NOT exclude meningitis. The classic triad of fever, neck stiffness, and altered consciousness is present in less than 50% of bacterial meningitis cases 1.

Diagnostic Performance

Sensitivity (ability to detect meningitis when present):

• Kernig's sign: 20-52% 2, 3, 4
• Brudzinski's sign: 20-53% 2, 3, 4
• Nuchal rigidity: 40-65% 2, 3

Specificity (ability to rule out meningitis when absent):

• Kernig's sign: 85-95% 2, 3, 4
• Brudzinski's sign: 85-95% 2, 3, 4
• Nuchal rigidity: 53-75% 2, 3

Clinical Application Algorithm

When meningitis is suspected, document:

1. Presence/absence of headache
2. Altered mental status (use Glasgow Coma Scale)
3. Neck stiffness
4. Fever
5. Rash (any type, especially petechial/purpuric)
6. Seizures
7. Signs of shock (hypotension, poor capillary refill) 1

Do NOT delay hospital referral or lumbar puncture based on negative meningeal signs 1

Key Pitfalls

• Elderly patients are more likely to have altered consciousness and LESS likely to have neck stiffness or fever 1
• Immunocompromised patients may have atypical presentations 5, 6
• Approximately half of meningitis patients will NOT present with typical meningeal signs 2
• Combining multiple examination findings improves diagnostic accuracy more than relying on any single sign 7, 2

What to Do Instead

Urgent hospital referral is mandatory when meningitis is suspected, regardless of physical examination findings 1. The diagnosis requires:

• Lumbar puncture with CSF analysis (leukocyte count, protein, glucose, culture, Gram stain) 5
• Blood cultures before antibiotics 5
• Immediate empiric antibiotics and dexamethasone if bacterial meningitis is suspected 8

Clinical concern from the referring physician or family members should always be taken seriously, even with negative examination findings 1.