Acute bacterial meningitis is a neurologic emergency, with symptoms developing over hours or days. Cerebrospinal fluid (CSF) studies show a neutrophilic pleocytosis, low glucose compared with blood glucose, and high protein. Cultures or bacterial antigens are positive. CSF pressure may be high. Delay in diagnosis and treatment can lead to permanent injury or death.

Viral meningitis is suggested by the constellation of fever, headache, and stiff neck; the cerebrospinal fluid (CSF) features include a lymphocytic pleocytosis, normal sugar, and negative culture for bacteria.

Chronic meningitis has a more indolent presentation, and may be associated with cranial nerve palsies, cognitive changes, or stroke-like events. The diagnosis of encephalitis (evidence of brain parenchymal involvement) is suggested, when the history includes fever, the acute onset of mental status changes (ranging from confusion to coma), seizures, and focal neurologic signs such as paralysis, acute psychosis, or aphasia. CSF shows
a lymphocytic pleocytosis with normal sugar. PCR for herpes simplex or other viral causes of encephalitis may be positive. MRI may show abnormalities in certain parts of the brain, such as the temporal lobe depending on the type of encephalitis.

The diagnosis of brain abscess is suggested by subacute fever, headache, focal signs or seizures, and signs of increased intracranial pressures. Fever is seen in approximately 50% of adults and up to 80% of children with brain abscess. Imaging shows a focal ring enhancing mass lesion or multiple lesions. CSF studies should not be performed to avoid herniation due to mass effect.

Check vital signs. Temperature may be higher in bacterial than in viral CNS infection. Herpes simplex encephalitis often results in a high fever (104°F-105°F). Tachycardia is seen in bacterial and viral CNS infection.

Check eardrums; examine sinuses for tenderness.

Check for stiff neck. Look for Kernig sign (with thigh flexed on abdomen, patient resists knee extension), or Brudzinski sign (attempt to flex the neck, results in reflex flexion of the knee and hip). Remember that the elderly, infants, and immunosuppressed patients may have meningitis without prominent meningeal signs. Comatose patients may not have meningismus.

Look for stigmata of chronic liver disease, and chronic lung disease as a predisposing factor for CNS infection.

Look for peripheral signs of embolization in a patient suspected of having subacute bacterial endocarditis or staphylococcal septicemia.

Examine the heart carefully (e.g., changing murmur in subacute bacterial endocarditis with valvular disease as source of septic embolism).

Examine for lymph-node enlargement or splenomegaly. These signs may suggest a lymphoproliferative disorder, in which CNS infections commonly are seen.

Is there evidence of CSF rhinorrhea caused by a defect or fracture in the cribriform plate?

Examine for petechial or purpuric lesions caused by meningococcemia, or staphylococcal bacteremia.

All patients suspected of having meningitis should have a lumbar puncture (LP), and treatment with antibiotics as soon as
possible (Table 24.1). Record the opening pressure. If focal neurologic symptoms or signs are present and brain abscess is a consideration, obtain a contrast-enhanced computed tomography (CT) or magnetic resonance imaging (MRI) scan first, but do not allow significant delay when there is a high likelihood of meningitis. If meningitis is a reasonable possibility and imaging is necessary, it may be appropriate to give IV antibiotics immediately. Blood cultures should be drawn before antibiotics are begun. See Chapter 30 for a discussion of CSF examination.

In addition, note the following points regarding meningitis and encephalitis: