Central Nervous System Infections
Recognition
Master bacterial meningitis, viral encephalitis, brain abscess, and shunt infection. Recognize fever, headache, neck stiffness, photophobia, altered mental status, and seizures; infants may show only poor feeding, irritability, or a bulging fontanel. Know that meningococcal disease can progress rapidly with petechiae and shock. Herpes simplex encephalitis classically causes temporal lobe findings, seizures, and behavioral change, and empiric acyclovir should not wait for confirmation.
Diagnosis and treatment
Understand that lumbar puncture is deferred when there are signs of raised intracranial pressure, focal deficit, or instability; blood cultures and empiric antibiotics come first. Know CSF patterns: bacterial (neutrophilic pleocytosis, low glucose, high protein), viral (lymphocytic, normal glucose), and the caveat that prior antibiotics alter results. Anticipate dexamethasone around first antibiotic dose for bacterial meningitis where appropriate, and seizure and ICP management.
Complications and prevention
Watch for hydrocephalus, hearing loss, SIADH, cerebral edema, and sepsis. Isolation precautions and chemoprophylaxis for close contacts apply to meningococcal and some other pathogens. Vaccination history is relevant.
Traps
Questions test that antibiotics are never delayed for lumbar puncture, that a normal CSF in early infection does not exclude disease, and that acyclovir dosing requires renal monitoring.
Rule of thumb
Sick child with fever and altered mental status: cultures, empiric antibiotics plus acyclovir, stabilize, then image and tap when safe.