Meningitis Overview and Types

Meningitis Overview

• Meningitis is an inflammation of the meninges, the protective membranes surrounding the brain and spinal cord.
• It can result from infections (bacterial, viral, fungal, parasitic) or non-infectious causes (autoimmune diseases, cancer, drug reactions).

Types of Meningitis

Bacterial Meningitis

• Pathogens: Commonly caused by Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae type B (Hib), and Listeria monocytogenes.
• Severity: Life-threatening, requiring urgent treatment.
• Transmission: Respiratory droplets or direct contact.

Viral Meningitis

• Pathogens: Often caused by enteroviruses, but also herpes simplex virus, varicella-zoster virus, or arboviruses.
• Severity: Less severe than bacterial; typically self-limiting.
• Transmission: Fecal-oral route, respiratory droplets, or insect bites.

Fungal Meningitis

• Pathogens: Usually caused by Cryptococcus neoformans or Histoplasma capsulatum.
• Risk Factors: Immunosuppressed individuals (e.g., HIV/AIDS).
• Transmission: Rare, typically through environmental exposure.

Parasitic Meningitis

• Pathogens: Caused by parasites like Naegleria fowleri (amoebic meningitis).
• Severity: Often fatal.
• Transmission: Associated with exposure to warm freshwater.

Non-infectious Meningitis

• Causes: Autoimmune diseases, malignancies, medications (e.g., NSAIDs, antibiotics), and trauma.

Pathophysiology

• Pathogens invade the central nervous system (CNS) via the bloodstream or direct extension from infected tissues.
• Inflammatory cytokines increase blood-brain barrier permeability, causing edema (brain swelling), increased intracranial pressure (ICP), altered cerebral perfusion, and neurological dysfunction.

Risk Factors

• Demographics: Infants and elderly are at higher risk. Community living (e.g., dormitories, military barracks) can increase risk.
• Medical Conditions: Immunosuppression (e.g., HIV/AIDS, cancer) and recent neurosurgery/head trauma increase risk.
• Vaccination Status: A history of inadequate vaccination against pathogens like Hib, meningococcal, or pneumococcal bacteria makes a person more susceptible.

Clinical Features

• Classic Triad: Fever, neck stiffness (nuchal rigidity), and altered mental status (confusion, drowsiness).
• Other Symptoms: Severe headache, photophobia (sensitivity to light), nausea, vomiting, and seizures (in severe cases).
• Infant Signs: Bulging fontanelle, poor feeding, irritability, and hypotonia.

Clinical Examination

• Kernig's Sign: Pain with knee extension when the hip is flexed.
• Brudzinski's Sign: Involuntary hip and knee flexion when the neck is flexed.

Diagnosis

• Lumbar Puncture: Analyses cerebrospinal fluid (CSF) to measure white blood cell count, glucose levels, protein levels, and presence of pathogens.
• Imaging: CT or MRI may be performed to rule out brain abscess or elevated ICP prior to lumbar puncture.

CSF Findings in Different Types of Meningitis

• CSF appearance, WBC count, glucose levels, and protein levels are characteristic of each type (bacterial, viral, fungal, tuberculous). See the table for further details

Management

• Bacterial Meningitis: Empiric antibiotics (based on age and risk factors). Neonates: Ampicillin + Cefotaxime or Gentamicin; Adults: Ceftriaxone + Vancomycin. Adjunct therapy includes dexamethasone to reduce inflammation.
• Viral Meningitis: Supportive care (hydration, pain relief, fever management) and antivirals (e.g., acyclovir for herpes-related cases) as appropriate.
• Fungal Meningitis: Antifungal therapy (e.g., Amphotericin B + Flucytosine).

Prevention

• Vaccinations: Hib, pneumococcal, and meningococcal vaccines.
• Prophylactic antibiotics for close contacts during outbreaks (e.g., rifampin in meningococcal exposure).
• Hygiene Measures: Frequent handwashing and avoidance of contact with infected individuals.

Complications

• Seizures
• Hydrocephalus
• Hearing loss
• Cognitive impairment
• Death (severe cases of bacterial meningitis)

Prognosis

• Bacterial Meningitis: High mortality without treatment; survivors may have lasting neurological deficits.
• Viral Meningitis: Generally good prognosis; resolves within 7-10 days.
• Fungal/Chronic Meningitis: Variable prognosis; depends on timely treatment and underlying immune status.