Introduction

Meningitis is an inflammation of the leptomeninges and the cerebrospinal fluid of the subarachnoid space. Viral meningitis is inflammation attributed to a viral agent. In comparison with bacterial meningitis, it may be considered to be a more benign condition and is much more common. Approximately 3,000 cases of confirmed viral meningitis are reported yearly, however, the actual number of cases is likely to be much higher, as patients often do not present to medical services.

Epidemiology

  • Incidence: 10.00 cases per 100,000 person-years
  • Most commonly see in infants
  • Sex ratio: more common in females 1:1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Aetiology

Patients at the extremes of age ( children under 5 years and the elderly) and those that are immunocompromised, for example, patients with renal failure, with diabetes, patients using intravenous drugs, are all more susceptible to infection and may experience a more severe and prolonged course of infection.

Pathophysiology

There are a number of organisms implicated in viral meningitis, the most common being the non-polio enteroviruses e.g. Coxsackie virus. Other pathogens include Mumps, Echovirus, Herpes Simplex Virus (HSV), Cytomegalovirus (CMV), Herpes Zoster Viruses, HIV, Measles, Influenza, and Arboviruses.

Clinical features

Patients almost always present with a headache, evidence of neck stiffness, photophobia (often milder than the photophobia experienced by a patient with bacterial meningitis), confusion, fevers and may have focal neurological deficits on examination, although again this is less frequently observed in viral as opposed to bacterial meningitis. Rarely, patients may experience seizures, however, these would tend to suggest a meningoencephalitis ( spread of the infection to the encephalon) rather than meningitis. Likewise, a significant change in behaviour, disorientation and or marked deterioration in mental state would be more in keeping with meningoencephalitis.

Investigations

Patients should undergo a lumbar puncture to confirm the diagnosis. Whilst awaiting the results of the lumbar puncture, treatment should be supportive and if there is any question of bacterial meningitis or of and encephalitis, the patient should be commenced on broad-spectrum antibiotics with CNS penetration e.g. ceftriaxone and aciclovir intravenously.

Cerebrospinal fluid findings in viral meningitis:

Opening Pressure10 - 20 cm³ H²O(10 – 20 cm³ H²O)
Cell count10-300 cells/µL(0 – 5 cells/µL)
Cell differentialLymphocytes(0 – 5 cells/µL lymphocyte predominant)
Glucose2.8 – 4.2 mmol/L or 2/3 serum glucose mmol/L( 2.8 – 4.2 mmol/L or 2/3 paired serum glucose mmol/L)
Protein0.5 - 1 g/dL(0.15 – 0.45 g/L)

Viral Polymerase Chain reaction (PCR) may demonstrate an underlying organism

Management

Generally speaking, viral meningitis is self-limiting, with symptoms improving over the course of 7 - 14 days and complications are rare in immunocompetent patients.