Clinical features:

Patients present with headache and necks stiffness. They typically have a fever, unless they are immunosupressed, and may have a rash. The classic triad in bacterial meningitis is headache, fever and rash. It is a serious life-threatening medical emergency that often results in significant disability. However, the commonest cause of meningits overall is viral meningitis; which is typically a self-limited disease. Mycobacteria tuberculosis (TB) also causes a meningitis that may have serious medical consequences such as meningovascular infarcts, arachnoiditis or hydrocephalus. Fungal infections can also cause meningitis and may often have a very indolant course before causing significant complictions such as vasculitis or hydrocephalus. Some fungal infections are more important in immunocompromised hosts. Lastly cancers may spread to the meningeal space and result in carcinomatous meningitis or lymphomatous meningitis, but the clinical presentation is usually different. Carcinomatous meningitis usually presents with polyradiculopathy rather than with headache. This section gives a brief overview of menigitis. The other subtypes are discussed elsewhere.
On physical examination patients may be normal, have meningismus, encephalopathy or be comatose. Fundoscopy may reveal papilloedema. When secondary injury occurs other focal features may develop.

Findings on investigations:

CSF analysis:

  • May be normal if hyperacute (rare), raised WCC +/-raised protein


  • Commonly normal
  • Cerebral oedema +/-herniation may occur
  • Distended subarachnoid space +/-distended basal cisterns
  • Communicating hydrocephalus: enlarged ventricles including 4th, effacement of basal cisterns


  • Commonly normal
  • Cerebral oedema +/-herniation
  • Distended subarachnoid space, communicating hydrocephalus
  • FLAIR: high signal in subarachnoid space, rarely parenchymal hyperintensity
  • DWI: high signal in sulci, hyperintense cortex if infarction or vasculitis occur
  • T1 +contrast: leptomeningeal enhancement that extends to the sulci may occur. Look at (basal cisterns, cerebellar folia, sulcal perivascular spaces)
Investigations to consider:
  • Blood cultures before antibiotics if feasible
  • CT head
  • CSF analysis, Lumber puncture. Note: exclude raised intracranial pressure and mass lesions before:
    • Cell count & differential, Glucose, protein, gram stain & culture


  • HIV testing; presence of HIV broadens the list of possible causes significantly
  • Bacterial antigen panel
  • Viral studies
  • Atypical bacteria & related:
    • Acid fast bacilli staining
    • TB PCR
  • Spirochetes: VDRL (CSF & Serum), Lyme serology (CSF & serum)
  • India ink preparation & culture
  • Tests for Rickettsia rickettsii (Rocky mountain spotted fever)
  • Fungal wet mount & culture
  • Cryptococcal antigen
  • Oligoclonal bands, IgG index
  • PCR for certain organisms as appropriate
  • Cytology: Metastasis
  • Flow cytometry: lymphomatous meningitis
  • Coccidioides: blastocysts
  • If a rash is present, skin scrapings & blood cultures
  • If TB meningitis is suspected, obtain systemic confirmatory tests as well as CSF TB PCR

CT or MRI: to assess for hydrocephalus or competing diagnosis

Causes of meningism:

  • Meningtitis: (see causes)
  • Subarachnoid hemorrhage
  • Pituitary infarction a.k.a. pituitary apoplexy


Causes of meningitis:

  • Bacterial meningitis:
    • Neisseria meningitides, Streptococcus pneumonia
    • Mycobacterium tuberculosis
  • Viral meningitis:
    • Enterovirus, coxasckie, echovirus
    • HSV2 & 1, VZV, EBV, CMV, HHV6-
    • Arboviruses:
      • St. Louis encephalitis virus, West Nile virus WNV, California encephalitis virus, western equine encephalitis virus, eastern equine encephalitis virus, Japanese B virus, Murray Valley virus, coltivirus.
    •  Zoonosis:
      • Lymphocytic choriomeningitis virus LCM
    • Mumps
    • HIV
  • Fungal meningitis:
    • Cryptococcus neoformans
  • Parasitic meningitis
  • Neoplastic meningitis/Metastatic meningitis:
    • Acute leukemia, Large cell lymphoma,
    • Breast cancer, lung cancer, melanoma, gastrointestinal malignancies, and cancers of unknown primary (CUP)
  • Chemical meningitis:
    • Drug induced meningitis: NSAIDs, Trimethorpim-sufamethoxazole TMP-SMX, IVIG, rofecoxib, OKT3 antibodies


Causes of lymphocytic meningitis (i.e. lymphocytic pleocytosis, i.e. mononuclear cells on CSF):

  • Viral meningitis (see viral meningitis)
  • TB meningitis
  • Listeria meningitis
  • Spirochetes:
    • Syphilis
    • Lyme disease
    • Leptosiprosis
  • Tickborn diseases (excluding arboviruses)
    • Rocky mountain spotted fever
    • Ehrlichiosis
  • Parameningeal infection & related:
    • Prevertebral abscess
    • Vertebral osteomyelitis
    • Bacterial endocarditis with cerebrospinal fluid seeding
    • Partially treated bacterial meninigitis
    • Sinusitis/otitis
  • Fungal meningitis:
    • Cryptococcus neoformans
    • Coccidioides immitis a.k.a. Coccidioidomycosis
  • Cerebral Malaria
  • Toxoplasmosis
  • Trypanosomiasis
  • Neoplastic meningitis/metastatic meningitis: (see neoplastic meningitis)
  • Others:
    • Vasculitis
    • Post-vaccinal encephalitis
    • Subarachnoid hemorrhage
    • Behcet’s syndrome
    • Sarcoidosis
    • Seizure (diagnosis of exclusion, low level pleocytosis)


Causes of meningitis with neutrophilic pleocytosis:


  • Bacterial meningitis and ruptured brain abscess (see bacterial meningitis)
  • West nile virus (WNV) meningitis (rare presentation)
  • Amebic meningoencephalitis


  • Drug induced meningitis: Sulfonamides, isoniazid, (see drug induced meningitis)
  • Chronic neutrophilic meningitis
  • NSAID meningitis in patients with collagen vascular disease
  • Severe juvenile idiopathic arthritis (JIA) a.k.a. Still’s disease

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