More than a century ago, Kernig and Brudzinski published descriptions of their eponymous signs for the bedside diagnosis of meningitis. At that time, most cases of meningitis were due to tuberculous or bacterial causes. In a contemporary reanalysis, which included patients with human immunodeficiency virus infection and used polymerase chain reaction technology to demonstrate viral causes of meningitis, Thomas and colleagues examined the diagnostic accuracy of Kernig's sign (increased meningismus pain with flexion of the neck), Brudzinski's sign (increased pain with re-extension of a flexed knee), and nuchal rigidity in patients with documented meningitis.
The study involved 297 adult patients presenting to an emergency department at a teaching hospital with symptoms suspicious for meningitis (fever, headache, nausea and vomiting, photophobia, stiff neck). Before lumbar puncture, physicians evaluated these patients for Kernig's sign, Brudzinski's sign, and nuchal rigidity. Objective evidence of meningitis (6 white blood cells [WBCs] per mL of cerebrospinal fluid [CSF] or more) was found in 27 percent of suspected cases.
Kernig's sign and Brudzinski's sign had very low sensitivity for detection of the documented meningitis cases (5 percent each). Furthermore, the majority of patients had discordant findings (positive for one sign, but negative for the other). Both tests had good specificity (95 percent), meaning that few patients without meningitis were thought to have positive examination signs. Nuchal rigidity was somewhat more useful as an indicator, but it still had limited sensitivity (30 percent). This additional sensitivity also came at the price of decreased specificity (68 percent).
Even in patients with “moderate”meningeal inflammation (at least 100 WBCs per mL of CSF) or “severe” disease (at least 1,000 WBCs per mL of CSF), Kernig's sign and Brudzinski's sign still had sensitivities under 25 percent. Nuchal rigidity was 100 percent sensitive in a very small subgroup of four patients with severe meningitis.
The authors concluded that the classic bedside examination maneuvers for the diagnosis of meningitis have low sensitivities and should not be relied on to determine whether patients with suspicious symptoms merit further diagnostic testing.