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Overview of Meningitis

by John E. Greenlee, MD

(For brain infections, see Brain Infections; for neonatal meningitis, Neonatal Bacterial Meningitis.)

Meningitis is inflammation of the meninges and subarachnoid space. It may result from infections, other disorders, or reactions to drugs. Severity and acuity vary. Findings typically include headache, fever, and nuchal rigidity, Diagnosis is by CSF analysis. Treatment includes antimicrobial drugs as indicated plus adjunctive measures.

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

  • Viral meningitis

  • Noninfectious meningitis

  • Recurrent meningitis

  • Subacute and chronic meningitis

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 viruses, noninfectious conditions (eg, drugs, disorders), or, occasionally, other organisms (eg, Borrelia burgdorferi in Lyme disease, Treponema pallidum in syphilis).

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):

  • Headache

  • Fever

  • Nuchal rigidity (meningismus)

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

  • Kernig sign (resistance to passive knee extension)

  • Brudzinski sign (full or partial flexion of the hips and knees when the neck is flexed)

  • Difficulty touching the chin to the chest with the mouth closed

  • Difficulty touching the forehead or chin to the knee

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

  • CSF analysis

Diagnosis is mainly by CSF analysis. Because meningitis can be serious and lumbar puncture see Lumbar puncture (spinal tap) 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 (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. 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. Also, if a bleeding disorder is suspected, lumbar puncture is not done until the bleeding disorder is excluded or controlled. If the skin over the needle insertion site is infected, the needle is inserted at a different site.

CSF Findings in Meningitis

Condition

Predominant Cell Type*

Protein*

Glucose*

Specific Tests

Normal CSF

All lymphocytes (0–5 cells/μL)

< 40 mg/dL

> 50 % of blood glucose

None

Bacterial meningitis

Leukocytes (usually PMNs), often greatly increased

Elevated

< 50% of blood glucose (may be extremely low)

Gram staining (yield is high if 10 5 colony-forming units of bacteria/ mL are present)

Bacterial culture

PCR if available

Viral meningitis

Lymphocytes (may be mixed; PMNs and lymphocytes during the first 24–48 h)

Elevated

Usually normal

Sometimes PCR (to check for enteroviruses or herpes simplex, herpes zoster, or West Nile virus)

IgM (to check for West Nile virus or other arboviruses)

Tuberculous meningitis

PMNs and lymphocytes (usually mixed pleocytosis)

Elevated

< 50% of blood glucose (may be extremely low)

Acid-fast staining

PCR

Mycobacterial culture (ideally using a CSF sample of ≥ 30 mL)

Interferon-γ tests of serum and (if available) CSF

Fungal meningitis

Usually lymphocytes

Elevated

< 50% of blood glucose (may be extremely low)

Cryptococcal antigen test

Serologic tests for Coccidioides immitis or Histoplasma sp antigen especially if patients have recently spent time in an endemic area

Fungal culture (ideally using a CSF sample of ≥ 30 mL)

India ink (for Cryptococcus sp)

*Changes in cell count, glucose, and protein may be minimal in severely immunocompromised patients.

In tuberculous meningitis, CSF acid-fast staining can be insensitive, sensitivity of PCR is only about 50%, and culture requires up to 8 wk. Positive CSF interferon-γ tests indicate tuberculous meningitis, but serum interferon-γ tests may only indicate prior infection. Thus, confirming a diagnosis of tuberculous meningitis is difficult, and if it is strongly suspected, even if not confirmed, it is treated presumptively.

A small number of cells may be present normally in neonates or after a seizure.

PCR = polymerase chain reaction; PMNs = polymorphonuclear neutrophils.

Treatment

  • Antimicrobial therapy as indicated

  • Adjunctive treatments

Infectious meningitis is treated with antimicrobial therapy as indicated clinically. Adjunctive treatments can include supportive measures, treatment of complications or of associated disorders, removal of causative drugs, and, for bacterial meningitis, corticosteroids.

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