Differential Diagnosis for Bacterial Meningitis

When considering whether bacterial meningitis should be considered in a patient's diagnosis, it's crucial to approach the differential diagnosis systematically. Here's a structured approach:

• Single Most Likely Diagnosis
  • Viral meningitis: This is often the most common cause of meningitis and presents similarly to bacterial meningitis but typically has a less severe course and is more common in adults. The justification for considering viral meningitis first lies in its higher prevalence compared to bacterial meningitis.
• Other Likely Diagnoses
  • Encephalitis: Inflammation of the brain tissue, which can be caused by viruses or other pathogens, and may present with symptoms overlapping those of meningitis, such as fever, headache, and altered mental status.
  • Subarachnoid hemorrhage: Bleeding into the space surrounding the brain can cause sudden, severe headache and stiff neck, mimicking meningitis.
  • Brain abscess: A collection of pus in the brain, which can cause fever, headache, and neurological deficits, and may be considered in the differential for meningitis, especially if there are focal neurological signs.
• Do Not Miss Diagnoses
  • Sepsis: A systemic infection that can lead to meningitis but also has a broad range of other presentations. Missing sepsis can be fatal, making it a critical diagnosis not to overlook.
  • Tuberculous meningitis: Although less common in many parts of the world, tuberculous meningitis has a high mortality rate if not treated promptly and should be considered, especially in high-risk populations or areas with high TB prevalence.
  • Fungal meningitis: Particularly in immunocompromised patients, fungal meningitis (e.g., cryptococcal meningitis) can present with similar symptoms to bacterial meningitis and requires specific treatment.
• Rare Diagnoses
  • Parasitic meningitis: Caused by parasites such as Naegleria fowleri (primary amebic meningoencephalitis), which is rare but almost always fatal if not treated immediately.
  • Mollaret's meningitis: A rare form of recurrent viral meningitis, typically caused by herpes simplex virus.
  • Chemical meningitis: Caused by non-infectious irritants, such as rupture of a dermatoid cyst or introduction of a foreign substance into the cerebrospinal fluid.

Each of these diagnoses has a unique set of risk factors, symptoms, and treatment approaches, emphasizing the importance of a thorough diagnostic evaluation when bacterial meningitis is considered.