Pathophysiology

Meningitis involves inflammation of the meninges, which are the protective layers around the brain and spinal cord. The disease process typically begins with an invading pathogen, which can be bacterial, viral, fungal, or even parasitic.

• Entry of Pathogen: Organisms often penetrate the body through the respiratory or gastrointestinal tract. Once in the bloodstream, they can traverse the blood-brain barrier, leading to CNS infection. Direct invasion can also occur due to injuries, surgeries, or congenital defects
• Inflammatory Response: The pathogen’s presence in the meninges induces inflammation. Pro-inflammatory cytokines are released, potentially causing cerebral edema and heightened intracranial pressure.
• Cerebral Edema: Brain tissue swelling may lead to compromised blood flow, possible herniation, and subsequent neurological damage.
• Complications: The inflammation can also result in complications such as hydrocephalus, cerebral abscesses, and subdural effusions.

Diagnostic Approach to Pediatric Meningitis

• Clinical Evaluation: An exhaustive history and physical examination are vital. Symptoms like fever, headache, and neck rigidity should be telltale signs.
• Lumbar Puncture: This procedure remains the gold standard for meningitis diagnosis. CSF analysis can show elevated white blood cell counts, raised protein levels, and reduced glucose, especially in bacterial meningitis. CSF cultures can pinpoint the causative organism.
• Blood Cultures: Useful for detecting septicemic forms or concurrent bloodstream infections.
• Neuroimaging: CT or MRI scans might be necessary for patients showing specific neurological signs, seizures, or altered mental status. These tools help rule out other potential causes and check for complications like abscesses or hydrocephalus.
• Rapid Diagnostic Tests: Techniques like PCR can swiftly detect viral or bacterial DNA in CSF, facilitating quicker diagnosis and treatment initiation..

Common bacterial pathogens include:

• Streptococcus pneumoniae – the most common cause of acute bacterial meningitis in children and adults. Spreads hematogenously from pneumonia or sinusitis. There is a second peak in adolescence.
• Neisseria meningitidis – second most common cause in children over 1 month old. Spreads via respiratory droplets. Most common in infants and adolescents/young adults. Often causes severe septicemia.
• Group B Streptococcus – Common in neonates, causes nearly half of cases in the first week of life due to perinatal transmission from mother.
• Listeria monocytogenes – Important pathogen in neonates, elderly, and immunocompromised persons. Spreads via ingestion of contaminated foods.
• Haemophilus influenzae – Now uncommon after introduction of Hib vaccine, but was a leading cause in children prior to widespread vaccination. Spreads via respiratory transmission.

The interplay between the pathogen’s virulence factors and the host’s inflammatory response determines the clinical course and outcome. Severe cases can lead to permanent neurologic damage, seizures, deafness, or death.