What is the key sign of meningitis on physical examination?

Nuchal rigidity is a key sign of meningitis and is characterized by an inability to flex the neck due to stiffness in the muscles. This symptom occurs when inflammation of the meninges— the protective membranes covering the brain and spinal cord— irritates the neck muscles. When clinicians assess for nuchal rigidity, they look for resistance or discomfort when attempting to flex the neck forward, often resulting in a reflexive arching of the back.

Recognizing nuchal rigidity during a physical examination can help distinguish meningitis from other conditions presenting with similar symptoms. Although fever, Brudzinski's sign, and photophobia are also associated with meningitis, nuchal rigidity is a more definitive physical finding. Fever is a common systemic symptom but not specific to meningitis. Brudzinski's sign, where the legs flex involuntarily when the neck is flexed, can indicate meningeal irritation but is not as direct as assessing nuchal rigidity. Photophobia, or sensitivity to light, can occur with meningitis but is more of a subjective symptom rather than an objective physical exam finding. Thus, nuchal rigidity stands out as a hallmark sign that indicates possible meningitis when conducting a physical examination.