Merck Manual

Please confirm that you are a health care professional

honeypot link

Overview of Meningitis


John E. Greenlee

, MD, University of Utah School of Medicine

Last full review/revision Dec 2020| Content last modified Dec 2020
Click here for Patient Education
Topic Resources

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 cerebrospinal fluid (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 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)

  • Occasionally, other organisms (eg, Borrelia burgdorferi in Lyme disease, Treponema pallidum in syphilis)

Symptoms and Signs of Meningitis

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):

  • 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 of Meningitis

  • Cerebrospinal fluid (CSF) analysis

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.


CSF Findings in Meningitis


Predominant Cell Type*



Specific Tests

Normal CSF

All lymphocytes† (0–5 cells/mcL)

< 40="">

> 50% of blood glucose


Bacterial meningitis

Leukocytes (usually PMNs), often greatly increased


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

Gram staining (yield is high if 105 colony-forming units of bacteria/mL are present)

Bacterial culture

Multiplex PCR panel if available

Viral meningitis

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


Usually normal

Multiplex PCR panel (if available) and/or conventional 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)


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

Acid-fast staining


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

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

Xpert MTB/RIF§

Fungal meningitis

Usually lymphocytes


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

Cryptococcal antigen test

Multiplex PCR panel if available (an adjunctive test, not to replace other tests)

Serologic tests for Coccidioides immitis or Histoplasma species 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. Blood glucose should be measured when lumbar puncture is done so that the CSF:serum glucose ratio can be determined.

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

‡ In tuberculous meningitis, CSF acid-fast staining can be insensitive, sensitivity of PCR is only about 50%, and culture requires up to 8 weeks. Positive CSF interferon-gamma tests indicate tuberculous meningitis, but serum interferon-gamma 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.

§ Xpert MTB/RIF (an automated rapid nucleic acid amplification test) may be used to detect M. tuberculosis DNA in CSF.

CSF = cerebrospinal fluid; PCR = polymerase chain reaction; PMNs = polymorphonuclear neutrophils.

Treatment of Meningitis

  • Antimicrobial therapy as indicated

  • Adjunctive treatments

Infectious meningitis is treated with antimicrobial therapy as indicated clinically.

Adjunctive treatments for meningitis can include

  • Supportive measures

  • Treatment of complications or of associated disorders

  • Removal of causative drugs

  • For bacterial meningitis, corticosteroids

Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
Professionals also read

Test your knowledge

Thiamine Deficiency
Thiamin deficiency causes beriberi. It is most common among patients with alcoholism and people subsisting on white rice or highly refined carbohydrates. Early symptoms of all types of beriberi are nonspecific and include fatigue, poor memory, anorexia, and abdominal discomfort. As beriberi progresses, different forms of this condition cause different symptoms. Of these symptoms, which of the following is most indicative of dry beriberi?
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID

Also of Interest

Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID