CNS Infections Overview

Study Notes

Infections can damage nervous tissue through direct injury, microbial toxins, inflammatory responses, or immune-mediated mechanisms.
Pathogens can enter the nervous system via four main routes: hematogenous spread, direct implantation, local extension, and transport along the peripheral nervous system.
Hematogenous spread is the most common method, typically through arterial circulation; retrograde venous spread is possible.
Direct implantation usually involves trauma or congenital malformations.
Local extension may originate from adjacent structures like air sinuses or infected teeth.
Certain viruses, such as rabies and herpes zoster, can travel via the peripheral nervous system.

Meningitis is inflammation of the meninges surrounding the brain and spinal cord.
Early recognition of CNS infections is vital due to high mortality rates and risk of permanent disability.
Different forms of meningitis include bacterial, tuberculous, viral meningoencephalitis, brain abscesses, fungal infections, and polio.

ABM is a common and serious medical emergency with a high cure rate if treated in time; otherwise, it can be fatal.
Early diagnosis is critical, typically via CSF examination.
Major cause of ABM includes Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae, and Listeria monocytogenes.

Streptococcus pneumoniae: Most frequent cause of bacterial meningitis in infants and adults, often following pneumonia or sinus infections; vaccine available.
Neisseria meningitidis: Causes meningococcal meningitis, spread via respiratory infections; outbreaks common in crowded settings; vaccine available.
Haemophilus influenzae: Once the leading cause in children; vaccination has significantly decreased cases.
Listeria monocytogenes: Found in unpasteurized foods; affects vulnerable populations, including pregnant women and newborns.

Most cases occur in children under five years old.
Risk factors include crowding, poverty, male gender, and absence of breastfeeding.

Pathophysiology involves bacterial colonization leading to bacteremia, affecting the choroid plexus and subsequently the meninges.
Results in meningeal exudates, encephalitis, and can lead to complications like infarction and increased intracranial pressure (ICP).

Symptoms: Sudden onset of high fever, headache, myalgia, photophobia, and neurological signs (convulsions, stupor, coma).
Increased ICP may lead to hypertension, bradycardia, bulging fontanelle, and cranial nerve palsies.
Purpuric rash may indicate meningococcal infection.

Diagnosed through CSF examination; key indicators include elevated pressure, turbid appearance, increased white cells (primarily neutrophils), high protein levels, and low glucose content.
Complications may include subdural effusions, empyema, hydrocephalus, and neurological deficits post-infection.