(See also Introduction to Brain Infections and Neonatal Bacterial Meningitis.)
Meningitis may be classified as acute, subacute, chronic, or recurrent. It may also be classified by its cause: bacteria, viruses, fungi, protozoa, or, occasionally, noninfectious conditions. But the most clinically useful categories of meningitis are
Acute bacterial meningitis is particularly serious and rapidly progressive. Viral and noninfectious meningitides are usually self-limited. Subacute and chronic meningitides usually follow a more indolent course than other meningitides, but determining the cause can be difficult.
Aseptic meningitis, an older term, is sometimes used synonymously with viral meningitis; however, it usually refers to acute meningitis caused by anything other than the bacteria that typically cause acute bacterial meningitis. Thus, aseptic meningitis can be caused by
Symptoms and Signs
Symptoms and signs of the different types of meningitis may vary, particularly in severity and acuity. However, all types tend to cause the following (except in infants and sometimes in the very old and in immunosuppressed patients):
Patients may appear lethargic or obtunded.
Nuchal rigidity, a key indicator of meningeal irritation, is resistance to passive or volitional neck flexion. Nuchal rigidity may take time to develop. Clinical tests for it, from least to most sensitive, are
Nuchal rigidity can be distinguished from neck stiffness due to cervical spine osteoarthritis or influenza with severe myalgia; in these disorders, neck movement in all directions is usually affected. In contrast, nuchal rigidity due to meningeal irritation affects mostly neck flexion; thus, the neck can usually be rotated but cannot be flexed.
Diagnosis
Meningitis is diagnosed mainly by CSF analysis. Because meningitis can be serious and lumbar puncture is a safe procedure, lumbar puncture should usually be done if there is any suspicion of meningitis. CSF findings tend to differ by the type of meningitis but can overlap.
If patients have signs suggesting increased intracranial pressure (ICP) or a mass effect (eg, focal neurologic deficits, papilledema, deterioration in consciousness, seizures, especially if patients have HIV infection or are immunocompromised), neuroimaging—typically, contrast-enhanced CT or MRI—is done before lumbar puncture. In such patients, lumbar puncture may cause brain herniation.
Also, if a bleeding disorder is suspected, lumbar puncture is not done until the bleeding disorder is excluded or controlled.
When lumbar puncture is deferred, blood cultures should be obtained, followed immediately by empiric treatment with antibiotics. After ICP has been lowered and if no mass is detected, lumbar puncture can be done.
If the skin over the needle insertion site is infected or if a subcutaneous or parameningeal lumbar infection is suspected, the needle is inserted at a different site, usually into the cisterna magna or the upper cervical spine at C2 using radiologic guidance.
