Meningitis is usually caused by bacterial, viral, or fungal infection, but can also result from injury, cancer, or drugs. Other factors that might suggest the likely aetiology include a patient’s immune status, travel history, and demographic factors such as their age. Classic symptoms of meningitis include headache, neck stiffness, photophobia, nausea or vomiting, and fever. Each type has characteristic risk factors, signs, and symptoms.
Viral meningitis is the most common cause of aseptic meningitis. Causative agents include human enteroviruses (most commonly), herpes simplex virus, mumps, arboviruses such as West Nile, HIV, and (rarely) influenza. Distinguishing viral from bacterial meningitis can be difficult and treatment with empirical antimicrobial therapy might be necessary while awaiting the results of cerebrospinal fluid analysis. Infants, immunocompromised patients, and those infected with herpes viruses or arboviruses are more likely to have complications. However, viral meningitis is typically self-limiting without serious sequelae.
Bacterial meningitis is a rare but serious inflammation of the meninges caused by various bacteria. Streptococcus pneumoniae, Haemophilus influenzae type b (Hib), and Neisseria meningitidis are the predominant causative pathogens in both adults and children. Individuals aged <2 months and >60 years are most commonly affected because of impaired or waning immunity. Rapid assessment and prompt antimicrobial therapy are essential.
Meningococcal infection may progress rapidly to septic shock with hypotension, acidosis, and disseminated intravascular coagulation. Prompt evaluation and treatment are essential, as the fatality rate and risk of severe complications are high.
A progressive, life-threatening, chronic or subacute meningitis that is most commonly caused by Cryptococcus species. It is often accompanied by systemic involvement in immunosuppressed patients. Infants and neonates are also at increased risk. Other causative agents include Coccidioides species, Candida species, or Histoplasma capsulatum.
Children with acute-onset rash accompanied by fever or systemic signs require urgent evaluation and treatment. One of the most life-threatening differentials is meningococcal septicaemia. Other infectious diseases presenting with skin rash in children that can result in meningitis as a complication include, for example, roseola infantum (sixth disease).
Tuberculous meningitis results from haematogenous spread of Mycobacterium tuberculosis with the development of submeningeal or intrameningeal foci called Rich foci. With rupture of a Rich focus into the subarachnoid space, meningitis develops. It may result from re-activation (more common in adults) or primary infection (more common in children). Diagnosis is dependent upon cerebrospinal fluid examination, and its rapid diagnosis is essential for improved outcomes.
Rabies is caused by negative-sense RNA viruses of the Lyssavirus genus. The virus enters the nervous system through unmyelinated sensory and motor terminals. Clinically, rabies has two forms: encephalitic (furious) and paralytic. Both forms have a prodrome of fever, chills, malaise, sore throat, vomiting, headaches, and paraesthesias.
Globally, this is a common sexually transmitted infection caused by the spirochete bacterium Treponema pallidum. Neurosyphilis is characterised by a chronic, insidious inflammation of the meninges, and is caused by central nervous system invasion by treponemes, which may occur at any stage of infection. Early neurosyphilis syndromes are usually the result of meningovascular involvement; infection may be asymptomatic or present with headache, meningism, hearing loss, seizures, or cranial nerve palsies. Late neurosyphilis may occur due to meningovascular involvement or direct infection of the brain and spinal cord parenchyma.
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This overview has been compiled using the information in existing sub-topics.
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