5th August 2024

Meningitis

Background

Meningitis describes inflammation of the meninges covering the brain and spinal cord. It is a potentially life-threatening neurological emergency requiring urgent treatment and assessment in secondary care. In addition to headache, symptoms also include neck stiffness, fever, photophobia, nausea and vomiting. The key diagnostic investigations are blood cultures and analysis of cerebrospinal fluid taken by lumbar puncture. Cases of meningitis with negative bacterial culture results (for example, viral, fungal and tuberculous meningitis) are referred to as aseptic meningitis. Empirical treatment is initiated on presentation with further treatment being tailored to investigation results.

Bacterial meningitis

Bacterial meningitis is a rare but life-threatening condition which is more common in very young and elderly people. The most common causative organisms include Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae and Listeria monocytogenes. The most severe symptoms are typically seen in meningococcal infection, with patients presenting with septic shock and the characteristic non-blanching rash (Figure 1). Listeria monocytogenes usually affects those who are at the extremes of age, immunocompromised or pregnant.

Treatment of bacterial meningitis

• In suspected bacterial meningitis, empirical antibiotic treatment should be initiated immediately.
• Due to the severity of the infection, cases of suspected meningococcal meningitis in the community should be treated with benzylpenicillin before transfer to hospital.
• For adults <50 years, empirical antibiotic treatment in the hospital consists of cefotaxime or ceftriaxone.
• For those >50 years, amoxicillin should be added to cover for Listeria.
• In suspected pneumococcal meningitis, dexamethasone should be started no later than 12 hours after the 1st antibiotic dose, as it has been shown to reduce mortality.
• The antimicrobial regime should then be reviewed with the CSF results and adjusted accordingly.
• Antimicrobial chemoprophylaxis is indicated for close contacts of those with confirmed meningococcal meningitis. Close contacts include household members, intimate contacts and anyone who has spent more than 8 hours less than 3 feet away from the person from 7 days before the onset of their symptoms to 24 hours after starting antibiotics. It also includes those who have had direct exposure to the patient’s oral secretions (for example, during intubation or suctioning) during this period.

Viral meningitis

Viral infections are the most common cause of meningitis and are usually self limiting. Common causes include human enteroviruses (most common), herpes simplex virus, varicella zoster virus and influenza.

Tuberculous meningitis

Tuberculous meningitis can occur in primary infection or reactivation. The onset of symptoms is typically slower than in other types of meningitis. Treatment is with anti-tuberculosis medications.

Fungal meningitis

Fungal infection is rare but life threatening. It is predominantly seen in those who are immunocompromised and is most commonly caused by infection with the cryptococcus species.

Aseptic meningitis

There are many other causes of aseptic meningitis, a small number of which will be outlined in this section:

• Primary HIV infection can present as meningitis which often resolves without treatment. It is, therefore, important to routinely screen for HIV in cases of meningitis.
• Mollaret’s meningitis is a recurrent meningitis which is defined as more than 3 episodes of meningism which resolve spontaneously. It is a rare condition and is usually caused by HSV (Herpes simplex virus)-2.
• Aseptic meningitis is a possible complication of mumps infection. Prior to the introduction of the mumps vaccine this was a very common cause of aseptic meningitis.
• Secondary syphilis, caused by the spherocyte Treponema pallidum, can present with meningism and a widespread rash.
• Acute lyme disease can present with a meningitic picture. It is a vector-borne disease caused by infection with Borrelia species which is spread by ticks. Cranial nerve palsies can be present, especially bilateral facial nerve palsy, which is characteristic of this disease. Another classical sign which would point towards this diagnosis is the presence of an erythema migrans rash.
• Rarely, aseptic meningitis can occur in response to a drug reaction. A variety of medications have been associated with this condition including NSAIDs, antibiotics and anti-epileptics.
• Malignant meningitis can occur with invasion by solid tumours or when haematological malignancies spread to the CNS.

Interpretation of cerebrospinal fluid results

Correct interpretation of cerebrospinal fluid (CSF) characteristics can indicate the diagnosis before culture results are available and, therefore, guide management decisions.

Image Source: James Heilman, M.D. Own work. CC BY-SA 3.0. Wikimedia Commons (2010). Vasculitis, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Vasculitis.JPG (Accessed: 16 January 2024)

Image Source: James Heilman, M.D. Own work. CC-BY-SA-4.0. Image Source: Wikimedia Commons (2019). MenigitisCSF2019, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:MenigitisCSF2019.jpg (Accessed: 16 January 2024)

References

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