Question
Aseptic meningitis
Answer
Aseptic meningitis is a clinical syndrome of meningeal inflammation in which routine bacterial (Gram stain and culture) testing of CSF is negative — the term “aseptic” reflects the absence of demonstrable pyogenic bacteria, not necessarily the absence of any infectious cause, since most cases are in fact caused by viruses.
Causative agents:
- Enteroviruses (coxsackieviruses, echoviruses) — the most common cause of viral (aseptic) meningitis overall, particularly in children, transmitted faecal-orally, typically causing a self-limiting summer/autumn-predominant illness.
- Herpesviruses — HSV-2 (more commonly than HSV-1) can cause a recurrent form (Mollaret’s meningitis); varicella-zoster virus; EBV; CMV (particularly in immunocompromised patients).
- Mumps virus — an important historical cause, now much reduced with MMR vaccination.
- Arboviruses — various, depending on regional epidemiology.
- Non-infectious/other causes: partially treated bacterial meningitis (prior antibiotics can sterilize CSF culture while inflammation persists), certain drugs (e.g., NSAIDs, IV immunoglobulin — drug-induced aseptic meningitis), and some autoimmune/malignant conditions can also produce an aseptic meningitis picture, an important differential to consider when a specific infectious cause cannot be identified.
Clinical/CSF features: fever, headache, neck stiffness, and photophobia, generally milder and more self-limiting than bacterial meningitis; CSF typically shows a lymphocytic pleocytosis (in contrast to the neutrophilic pleocytosis of bacterial meningitis), normal or only mildly raised protein, and normal glucose (in contrast to the markedly reduced glucose of bacterial meningitis) — this CSF profile is a key distinguishing feature guiding the initial differential diagnosis, though early viral meningitis can occasionally show an initial neutrophilic predominance before shifting to lymphocytic.
Laboratory diagnosis: CSF PCR (for enteroviruses, HSV, VZV, etc.) is the primary diagnostic method where available; viral culture is less commonly used now given lower sensitivity and slower turnaround; serology has limited utility for acute diagnosis.
Management: primarily supportive, since most viral causes are self-limiting; specific antiviral therapy (e.g., acyclovir) is used when HSV is suspected/confirmed, given the potential for progression to encephalitis if untreated; importantly, bacterial meningitis must be actively excluded/treated empirically pending results, since a falsely reassuring “aseptic” label applied too early (before culture results are available) in a patient who actually has bacterial meningitis could be catastrophic.