When to suspect bacterial meningitis
The pathogen Neisseria meningitidis attacks the brain's meningeal layer
A 32-year-old software engineer comes to your office because he has been having headaches and fever for the past two days. A fever of 105.5°F forced him to cancel a business trip. The patient complains of the worst headache of his life. He is otherwise healthy and sees you only for annual checkups. Physical exam is significant for obvious distress (the patient needs to lie in the room without any lights on). He is febrile to 104.9°F in your office and has a stiff neck, raising his legs when you lift his head on the exam table. His neurologic exam is normal, and his wife, who brought him to the office, has noticed no evidence of confusion or somnolence. Skin exam is also normal. What is the diagnosis?
Bacterial meningitis is an uncommon but serious event in clinical practice. Its presentation is dramatic, and rapid diagnostics are essential in order to obtain necessary information for treatment as well as prognosis. Bacterial infection of the meninges is the worst-case scenario but is potentially treatable if picked up early, putting extra pressure on the clinician to act quickly. Viral infections are usually less serious but more common, needing only supportive care (with one important exception to be discussed later).
Recent epidemiologic studies estimate the incidence of bacterial meningitis to be about three cases per 100,000 population in the United States. Predisposing risk factors include diabetes mellitus, alcohol abuse, and other infections (e.g., sinusitis, otitis media, or pneumonia). Infection of the meninges and subarachnoid space occur when the pia mater, arachnoid space, or dural meninges are broached by an invasive pathogen, leading to the clinical findings of meningitis. The more usual organisms include Streptococcus pneumoniae, Hemophilus influenzae, and Neisseria meningitidis; others include Listeria monocytogenes as well as some more unusual bacteria.
Patients typically present with a sudden illness characterized by fever, neck pain, and altered mental status (Table 1). Photophobia is a hallmark feature, as is nuchal rigidity. In this case, pain occurs not only on passive motion of the neck but also with associated meningeal irritation, which results in spontaneous flexion of the hips during passive flexion of the neck (Brudzinski sign) or inability to fully extend the knees when the hips are flexed at 90° (Kernig test). Although enshrined in medical school textbooks, modern data have suggested that these bedside tests are neither sensitive nor specific. Extrameningeal signs are nonspecific except for purpura, which can be the most dramatic and frightening associated exam finding. Purpura is highly suggestive of meningococcal infection but seen only on rare occasions.