Viral Meningitis

Related Subjects: |Herpes Varicella-Zoster (Shingles) Infection |Chickenpox Varicella Infection |Varicella Cerebral Vasculopathy |Herpes Viruses |Herpes Zoster Ophthalmicus (HZO) Shingles |MonkeyPox |Mumps |Measles |Rubella (German Measles) |Epstein-Barr Virus infection |Cytomegalovirus (CMV) infections |CMV retinitis infections |Toxoplasmosis

🧠 Key Exam Pearl: Viral meningitis is generally milder than bacterial meningitis, but the clinical overlap means you must always exclude bacterial meningitis and HSV encephalitis first. 📌

📖 About

• Viral Meningitis: Infection of the meninges caused by viruses. Usually self-limiting but can cause significant symptoms.
• Key Differentials: Exclude bacterial meningitis 🧫 (life-threatening, requires antibiotics) and viral encephalitis ⚡ (often HSV, requires IV aciclovir).
• Seasonality: More common in late summer and autumn.
• Symptoms: Fever 🌡️, headache 🤕, neck stiffness, and photophobia 😵‍💫.

🦠 Causes

• Enteroviruses: Account for 77–90% of cases, especially in children during summer.
• Arboviruses: Tick-borne or mosquito-borne; often cluster cases. May mimic Lyme disease ➝ use CSF IgM for diagnosis.
• Herpes Viruses:
  • HSV-2: More often meningitis (may follow genital lesions).
  • HSV-1: More commonly encephalitis.
  • VZV: May follow chickenpox or shingles.
• HIV: Can cause meningitis during acute seroconversion ➝ sometimes with cranial neuropathies.
• EBV: May complicate infectious mononucleosis.
• Mumps: Winter/spring, more common in males; associated with orchitis. 📉 Incidence has dropped with MMR vaccination.
• Lymphocytic Choriomeningitis Virus (LCMV): Linked to mice 🐭 exposure in autumn; systemic features include rash, pulmonary changes, alopecia, orchitis, parotitis.
• Others: CMV, measles, rare viral causes.

🧾 Clinical Presentation

• Fever + meningism (headache, neck stiffness, photophobia).
• Frontal headache, worsened by eye movements 👀.
• Skin rash may accompany enteroviral and arboviral causes.
• Vomiting/diarrhoea can occur with enteroviral illness.
• Red flag: Confusion or seizures ➝ think viral encephalitis (esp. HSV).
• Mollaret’s meningitis: Recurrent meningitis due to HSV-2.

🧪 Investigations

• CSF analysis:
  • Lymphocytes <100/µL
  • Mild ↑ protein
  • Normal glucose
  • ⚠️ If lymphocytes + low glucose ➝ consider TB, fungal meningitis, Listeria, or inflammatory causes (e.g. sarcoidosis).
• CSF PCR: Gold standard for identifying viral DNA/RNA (HSV, VZV, CMV, EBV, enterovirus).
• HIV testing: Consider if HIV meningitis suspected.
• Imaging: CT/MRI if focal signs, seizures, or to exclude abscess/SOL before LP.

⚖️ Differential Diagnosis

• Bacterial meningitis: More severe; treat empirically until excluded.
• HSV Encephalitis: Focal neurology, seizures, altered consciousness; treat immediately with IV aciclovir.
• Brain abscess: Raised ICP, focal deficits ➝ imaging essential.
• Cryptococcal meningitis: Particularly in HIV/AIDS patients.

💊 Management

• Exclude bacterial meningitis: Start empiric antibiotics if uncertain, pending results.
• Aciclovir: If HSV suspected (esp. with genital HSV-2 or temporal lobe features).
• Supportive care: Hydration 💧, analgesia, antiemetics.
• HIV meningitis: Liaise with infectious diseases for antiretroviral timing.
• Prognosis: Usually good 👍. Most recover fully, though some have prolonged fatigue or headaches. Neonates/infants may suffer intellectual impairment.

📌 Exam Tip: Viral meningitis ➝ normal CSF glucose; TB/fungal ➝ ↓ glucose. 🚩 Always treat first for bacterial/HSV meningitis if unsure – viral causes are self-limiting, but bacterial/HSV can be fatal if missed.

Cases - Viral Meningitis

• Case 1 - Enterovirus Meningitis in a Young Adult: A 22-year-old university student presents with fever, headache, photophobia, and neck stiffness. He is alert and oriented. No focal neurology. CT head is normal. LP: clear CSF, lymphocytic pleocytosis, mildly raised protein, normal glucose. PCR positive for enterovirus. Diagnosis: Viral meningitis (enterovirus). Management: Supportive - fluids, analgesia, antipyretics; no antibiotics once diagnosis confirmed. Good prognosis.
• Case 2 - HSV-2 Meningitis in an Immunocompromised Patient: A 38-year-old woman with poorly controlled HIV presents with headache, fever, and photophobia. Exam: meningism but no confusion or seizures. CSF: lymphocytosis, raised protein, normal glucose. PCR positive for HSV-2. Diagnosis: Viral meningitis due to HSV-2. Management: IV aciclovir in immunocompromised host; supportive care; HIV treatment optimisation.

Teaching Commentary 🧠

Viral meningitis is usually self-limiting, with enteroviruses (e.g. echovirus, coxsackievirus) the most common cause. HSV, VZV, mumps, and HIV are other important culprits. CSF findings: clear fluid, lymphocytosis, mildly elevated protein, and normal glucose. Unlike encephalitis, consciousness and focal neurology are preserved. Management is supportive, except HSV/VZV meningitis in immunocompromised patients, where aciclovir is indicated. Prognosis is excellent in most immunocompetent adults.