22nd May 2024

Central Nervous System Infection

Central nervous system infection

Background

Central nervous system (CNS) infections can lead to meningitis and encephalitis. The cause can be any infection, whether bacterial, viral, fungal or protozoan. Systemic illnesses such as SLE or sarcoid, medication and intracranial tumours can also lead to inflammation of the meninges. Differentiating these quickly and commencing treatment is vital.

Viral infection

Enteroviruses, herpes and arboviruses are the most common viral causative organisms. Herpesviruses encompass a wide array of viruses including HSV type 1 and 2, VZV (varicella zoster), CMV, EBV and HHV (human herpesvirus) 6,7 and 8. HSV encephalitis, usually caused by HSV1, can be a fatal infection as opposed to aseptic meningitis caused by HSV2, which is self-limiting.

Enteroviruses account for 48-95% of cases of aseptic meningitis syndrome. In addition to meningitis, it can also cause acute flaccid paralysis (Guillain-Barre syndrome), encephalitis and myocarditis with the worst presentations occurring in infants. Older people have better clinical outcomes with enterovirus-related aseptic meningitis. Transmission is via the faecal-oral route.

Bacterial infection

Haemophilus influenzae is the most common causative bacterial infection. Neisseria meningitidis and Streptococcus pneumoniae are also common, with Listeria monocytogenes common in older immunocompromised patients.

Clinical features

Both bacterial and viral CNS infections can present similarly. Bacterial meningitis leads to a triad of headaches, fever and nuchal rigidity. Confusion, lethargy, nausea and vomiting may also be present. Viral meningitis often has a flu-like prodrome. Features of meningoencephalitis, such as altered consciousness and focal neurological deficits, may also be present.

Investigations

The mainstay of investigation is lumbar puncture. As well as basic investigations such as microscopy and gram stain, cell count, glucose and protein, other investigations may also be indicated. This can include culture for tuberculosis, PCR for viral causes, Toxoplasma serology and fungal culture, amongst others. CT and MRI imaging are also used and can provide a clue to aetiology.

Management

Empirical antibiotics in the initial stages of management are important. Ceftriaxone is often used. Acyclovir and IV Dexamethasone can also play a role.

References

• Bennett, J, Dolin, R, Blaser, M. Mandell, Douglas and Bennett’s Principles and Practice of Infectious Disease 9ᵗʰ Edition. Philadelphia Elsevier. 2019.
• Torok E, Moran E, Cooke F. Oxford Handbook of Infectious Diseases and Microbiology, 2ⁿᵈ Edition. Oxford. Oxford University Press. 2017.