What are the signs and workup for viral meningitis?

Signs and Workup for Viral Meningitis

Viral meningitis should be suspected in patients presenting with meningism (neck stiffness, headache, and photophobia) and requires prompt cerebrospinal fluid examination for diagnosis, unless contraindications for lumbar puncture are present. 1

Clinical Presentation

• Patients with viral meningitis typically present with meningism, characterized by neck stiffness, headache, and photophobia 1
• Fever may be present but is not universal in viral meningitis cases 1
• Non-specific symptoms often accompany the presentation, including diarrhea, vomiting, muscle pain, and sore throat 1
• Unlike bacterial meningitis, there is usually no reduced level of consciousness in adults with viral meningitis; altered mental status suggests an alternative diagnosis 1
• HSV-2 meningitis patients rarely have concurrent genital ulcers and often lack any history of genital disease 1
• VZV meningitis can occur with or without the characteristic rash of chickenpox or shingles 1

Diagnostic Approach

Initial Assessment

• Lumbar puncture (LP) is the cornerstone of diagnosis for suspected viral meningitis 1
• LP should be delayed if any of the following contraindications are present 1:
  • Signs of severe sepsis or rapidly evolving rash
  • Respiratory or cardiac compromise
  • Anticoagulant therapy or known thrombocytopenia
  • Infection at the LP site
  • Focal neurological signs (requires neuroimaging first)
  • Presence of papilloedema (requires neuroimaging first)
  • Continuous or uncontrolled seizures (requires neuroimaging first)
  • Glasgow Coma Scale ≤12 (requires neuroimaging first)

CSF Analysis

• CSF opening pressure should always be measured (unless LP is done in sitting position) 1
• CSF cell count typically shows pleocytosis, though patterns vary 1:
  • Viral meningitis usually shows lymphocyte predominance, but neutrophils may predominate in early enteroviral meningitis
  • Total CSF white cell count rarely exceeds 2000 cells/mm³ in viral cases 1
• CSF biochemistry findings suggestive of viral rather than bacterial etiology 1:
  • CSF protein typically lower than in bacterial meningitis (often <0.6 g/L)
  • CSF glucose usually normal or only slightly reduced (typically >2.6 mmol/L)
  • CSF:plasma glucose ratio usually >0.36 (normal is approximately 2/3)
  • CSF lactate levels are typically normal in viral meningitis

Microbiological Testing

• CSF PCR is the gold standard for confirmation of viral meningitis 1
• When viral meningitis is suspected, CSF should be tested for 1, 2:
  • Enteroviruses (most common cause)
  • Herpes simplex viruses type 1 and 2 (HSV-1 and HSV-2)
  • Varicella zoster virus (VZV)
• Additional viral testing should be guided by clinical features, immune status, and travel history 1
• Stool and/or throat swabs should be tested for enterovirus by PCR 1
• PCR multiplex testing can be particularly valuable in patients who have received empiric antibiotics before lumbar puncture 3

Differential Diagnosis

• Bacterial meningitis - distinguished by more severe presentation, altered mental status, and different CSF profile 1
• Encephalitis - distinguished by altered consciousness and focal neurological signs 1
• Subarachnoid hemorrhage - can mimic meningitis symptoms 1
• Space-occupying lesions - may present with headache and altered mental status 1
• Encephalopathy due to infection outside the central nervous system 1

Common Etiologies

• Enteroviruses are the most common cause (>90 serotypes exist) 1, 2
• Herpes viruses, predominantly HSV-2 and VZV, are the second most common cause 1, 2
• Less common viral causes include cytomegalovirus, Epstein-Barr virus, and mumps virus 1, 2
• No specific pathogen is identified in 30-50% of presumed viral meningitis cases 1

Management Considerations

• Viral meningitis should be assessed by an infection or neurological specialist 1
• Identifying the viral pathogen allows for appropriate diagnosis, cessation of unnecessary antibiotics, reduction in investigations, and shorter hospital stays 1
• Currently, there are no treatments of proven benefit for most causes of viral meningitis 1
• Some clinicians treat herpes meningitis with aciclovir or valaciclovir, but evidence supporting this practice is lacking 1

Important Pitfalls to Avoid

• Do not rule out meningitis based solely on absence of classic symptoms, as these may not be present in all cases 1
• Do not rely on Kernig's sign or Brudzinski's sign alone, as they have low sensitivity (11% and 9% respectively) for diagnosing meningitis 1
• Do not delay antimicrobial therapy if bacterial meningitis is suspected while awaiting imaging or LP 1
• Do not assume normal CSF cell count excludes infection; early in the course of illness, CSF white cell count may be minimal or absent 1
• Do not routinely use aciclovir/valaciclovir as prophylaxis for recurrent herpes meningitis (HSV or VZV) 1