What are the signs of viral meningitis?

Signs of Viral Meningitis

Viral meningitis presents with headache (universally present), fever, neck stiffness, photophobia, nausea, and vomiting, though the clinical presentation overlaps substantially with bacterial meningitis and cannot reliably distinguish between the two without cerebrospinal fluid examination. 1, 2

Core Clinical Features

Universal and Near-Universal Symptoms

• Headache is present in 100% of viral meningitis cases and is typically severe, bilateral, and often throbbing in quality 2
• The headache may be of abrupt onset or described as "the worst headache of the patient's life" in approximately 60% of cases 2
• Fever is common but not universal, occurring in approximately 73% of viral meningitis patients 2

Common Associated Symptoms

• Photophobia or hyperacusis occurs in a substantial proportion of patients 1, 2
• Neck stiffness (meningismus) is present in approximately 44-61% of cases 2, 3
• Nausea and/or vomiting occur in 29-61% of patients 2, 3
• The classic triad of headache, neck stiffness, and photophobia/hyperacusis is present in only 28% of cases 1

Prodromal and Additional Features

• Approximately 46% of patients report prodromal symptoms including malaise, myalgia, gastrointestinal symptoms, or urinary tract symptoms 2
• Back pain may be present in some cases 2
• Self-reported fever occurs in 45% of HSV-2 meningitis cases specifically 3

Critical Diagnostic Limitations

Poor Discriminatory Value of Clinical Signs

• Clinical examination alone cannot reliably distinguish viral from bacterial meningitis 4, 5
• Classic meningeal signs (Kernig and Brudzinski) have extremely poor sensitivity: Kernig sign 11-53% and Brudzinski sign 9-66%, depending on age group 4, 6, 5
• Neck stiffness has a sensitivity of only 31-51% for meningitis overall 6, 5, 7
• The absence of fever, neck stiffness, headache, and altered mental status together has a 95% negative predictive value for ruling out meningitis 7

Mandatory CSF Examination

• Cerebrospinal fluid analysis is essential and cannot be bypassed based on clinical presentation alone 4, 5
• CSF in viral meningitis typically shows elevated protein (mean 156 g/dL), elevated white cell count (mean 160-504 cells/μL), and normal glucose 1, 3
• No diagnostic algorithm for distinguishing bacterial from viral meningitis has 100% sensitivity 4, 5

Age and Pathogen-Specific Considerations

Etiology Distribution

• Enteroviruses account for 39% of cases, HSV-2 for 16%, varicella-zoster virus for 15%, with 27% remaining unidentified despite testing 1
• HSV-2 meningitis shows a strong female predominance (77-83%) and may not correlate with active genital herpes symptoms 1, 3
• Varicella-zoster virus meningitis frequently occurs with immunosuppression (20%) or shingles (60%) 1

Neuroimaging Findings

• Brain imaging is typically normal (83%) when performed, though some cases show nonspecific (14%) or meningeal changes (3%) 3
• Computed tomography is negative in all cases when performed for viral meningitis 2

Common Pitfalls to Avoid

• Do not rely on the absence of classic signs to rule out meningitis - characteristic symptoms may be absent in both viral and bacterial cases 4, 6
• Do not assume fever must be present - up to 27% of viral meningitis patients may be afebrile 2
• Do not use clinical features alone to differentiate viral from bacterial meningitis - empiric antibiotics should be initiated while awaiting CSF results if bacterial meningitis cannot be excluded 4, 5
• The presence or absence of focal neurologic findings, altered consciousness, or papilledema does not reliably distinguish viral from bacterial etiology 2

Prognosis

• Approximately 20% of patients have an unfavorable outcome (Glasgow Outcome Scale 1-4) at 30 days post-discharge, with females having a 34% increased risk 1
• Outcomes are similar across different viral etiologies, including cases where no pathogen is identified 1
• Long-term neurological disability and death are rare in viral meningitis 3