Meningitis: Causes, Symptoms, Diagnosis, and Treatment Protocols

Posted on Oct 15, 2025 in Microbiology

Meningitis: Etiology, Clinical Features, Diagnosis, and Management

Meningitis is a critical medical condition requiring immediate attention. This document details the etiopathogenesis, clinical features, diagnosis, and management strategies for this inflammation of the meninges.

1. Etiopathogenesis of Meningitis

Meningitis refers to inflammation of the meninges, the protective membranes covering the brain and spinal cord. It may be caused by infectious or non-infectious agents.

Etiology:

• Infectious causes:

  • Bacterial (the most serious form):

    • Neonates: Group B Streptococcus, Escherichia coli (*E. coli*), Listeria monocytogenes

    • Children: Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae type b

    • Adults/Elderly: S. pneumoniae, N. meningitidis, Listeria, Gram-negative bacilli

  • Viral (aseptic meningitis):

    • Enteroviruses (e.g., Coxsackie, Echovirus), HSV-2, VZV, HIV, Mumps virus

  • Fungal: Cryptococcus (especially in immunocompromised patients)

  • Tuberculous meningitis: Caused by Mycobacterium tuberculosis

• Non-infectious causes:

  • Autoimmune diseases (e.g., Systemic Lupus Erythematosus)

  • Neoplastic infiltration

  • Drug-induced (e.g., NSAIDs, IVIG)

Pathogenesis:

1. Entry of pathogen via hematogenous spread or direct extension (e.g., from sinuses, otitis, trauma, neurosurgery).

2. Crossing the blood-brain barrier (BBB) into the subarachnoid space.

3. Immune activation in the Central Nervous System (CNS) leading to inflammation and increased vascular permeability.

4. Resulting in cerebral edema, increased intracranial pressure (ICP), and potential neuronal damage.

2. Clinical Features and Symptoms

Classic Triad (especially in bacterial meningitis):

• Fever

• Neck stiffness (Nuchal rigidity)

• Altered mental status (confusion, lethargy, coma)

Other Symptoms:

• Severe, generalized headache

• Photophobia (sensitivity to light)

• Nausea and vomiting

• Seizures

• Focal neurological signs

• Positive Kernig’s and Brudzinski’s signs

Atypical Presentation in Infants and Elderly:

• Bulging fontanelle (infants)

• Poor feeding, lethargy

• Hypotonia

• Seizures

• Altered sensorium

Meningococcal Meningitis Specifics:

• May present with a petechial rash or purpura

• Rapid progression to septic shock and Disseminated Intravascular Coagulation (DIC)

3. Diagnosis and Investigations

Initial Assessment:

• Vital signs and comprehensive neurological examination

• Assessment for signs of raised ICP (e.g., papilledema, altered consciousness)

Key Investigations:

Lumbar Puncture (LP) – The Gold Standard

• Cerebrospinal Fluid (CSF) analysis:

  Parameter	Bacterial	Viral	Tuberculous/Fungal
  Appearance	Turbid	Clear	Clear or slightly cloudy
  Opening pressure	↑↑ (Markedly increased)	Normal or slightly ↑	↑ (Increased)
  WBC count	↑↑ (Predominantly Neutrophils)	↑ (Predominantly Lymphocytes)	↑ (Predominantly Lymphocytes)
  Protein	↑ (Increased)	Normal or slightly ↑	↑↑ (Markedly increased)
  Glucose	↓ (Decreased)	Normal	↓ (Decreased)
  Gram stain	May show bacteria	Negative	AFB stain, PCR useful

Important Note: A CT head scan must precede LP if there are signs of raised ICP, focal neurological deficits, or an immunocompromised state.

Blood Tests:

• Complete Blood Count (CBC), C-Reactive Protein (CRP), Erythrocyte Sedimentation Rate (ESR)

• Blood cultures (must be drawn before administering antibiotics)

• Polymerase Chain Reaction (PCR) for viral causes (e.g., HSV, enteroviruses)

Imaging:

• CT or MRI scan if a space-occupying lesion, raised ICP, or complications (hydrocephalus, abscess) are suspected.

4. Management and Treatment Protocols

General Principles:

• Meningitis is a Medical Emergency – treatment must be initiated immediately.

• Administer Empiric antibiotics as soon as possible (ASAP) after blood cultures are drawn, even if the LP is delayed.

Empiric Antibiotic Therapy:

• Add Acyclovir if viral encephalitis is suspected (especially Herpes Simplex Virus).

• Antitubercular therapy is required for Tuberculous meningitis.

• Antifungals (e.g., Amphotericin B + flucytosine) are used for cryptococcal meningitis.

Adjunctive Therapy:

• Dexamethasone: Recommended, especially in meningitis caused by S. pneumoniae or H. influenzae, as it reduces complications like hearing loss.

• Supportive care:

  • IV fluids and electrolyte management

  • Antipyretics for fever control

  • Anticonvulsants for seizure management

  • Intracranial Pressure (ICP) management (e.g., using mannitol)

5. Potential Complications

• Seizures

• Hearing loss (a common sequela of H. influenzae meningitis)

• Hydrocephalus

• Subdural effusion

• Brain abscess formation

• Long-term cognitive deficits or learning disabilities

• Death

6. Prevention Strategies

• Vaccination:

  • Haemophilus influenzae type b (Hib) vaccine

  • Pneumococcal conjugate vaccine (PCV)

  • Meningococcal vaccine

• Chemoprophylaxis: Recommended for close contacts of meningococcal cases (e.g., using Rifampin or Ciprofloxacin).

For further academic study or revision, consider focusing on the differential diagnosis based on CSF parameters.