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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Do not delay empiric antibiotics for CT or LP if bacterial meningitis is suspected
- Bacterial CSF: high opening pressure, neutrophils, low glucose, high protein
- Adults usually receive vancomycin plus ceftriaxone; add ampicillin for Listeria risk
- Add acyclovir if encephalitis is suspected
- Give dexamethasone before or with first antibiotics when pneumococcal meningitis possible
Overview
Meningitis is meningeal inflammation from infection. Bacterial meningitis is rapidly fatal without treatment; viral meningitis is often self-limited except HSV/VZV and high-risk hosts. Encephalitis suggests brain involvement with altered mental status, seizures, or focal deficits.
Epidemiology
Common adult bacterial causes are Streptococcus pneumoniae and Neisseria meningitidis. Listeria affects older, pregnant, alcoholic, and immunocompromised patients. Viral causes include enterovirus, HSV, VZV, HIV, and arboviruses.
Clinical Features
Symptoms
Fever, severe headache, photophobia
Neck stiffness or pain with neck flexion
Confusion, lethargy, altered mental status
Seizures or focal deficits suggest encephalitis/complication
Petechial rash suggests meningococcemia
Signs
Nuchal rigidity, Kernig/Brudzinski signs
Sepsis physiology or hypotension
Papilledema or focal deficit before LP is concerning
Vesicular rash may suggest HSV/VZV
Bulging fontanelle in infants
Investigations
First-line
Blood culturesBefore antibiotics if this does not delay treatment
Lumbar punctureOpening pressure, cell count, glucose, protein, Gram stain/culture, PCR
CSF profileBacterial neutrophils/low glucose/high protein; viral lymphocytes/normal glucose
Second-line
CT head before LPImmunocompromised, mass lesion, seizure, papilledema, altered consciousness, focal deficit
CSF PCREnterovirus, HSV, VZV as indicated
CBC/CMP/lactate/coagsSepsis severity and dosing
Specialist
MRI brainEncephalitis, abscess, focal findings, persistent symptoms
EEGNonconvulsive seizures or HSV encephalitis
1
Empiric treatment
- Give antibiotics immediately after blood cultures when possible
- Dexamethasone before/with first antibiotic dose
- Droplet precautions for suspected meningococcus
- Support airway, sepsis, seizures, and sodium/glucose problems
2
Adult regimens
- Age 2-50: vancomycin + ceftriaxone/cefotaxime
- Age >50/pregnancy/alcoholism/immunocompromised: add ampicillin
- Post-neurosurgery/shunt: vancomycin + cefepime/ceftazidime/meropenem
- Narrow once organism known
3
Viral/encephalitis
- Supportive care for uncomplicated enterovirus
- IV acyclovir immediately for suspected HSV encephalitis
- Treat VZV CNS disease with acyclovir
- Stop antibiotics when bacterial disease excluded and stable
4
Public health
- Meningococcal contacts need rifampin/ciprofloxacin/ceftriaxone prophylaxis
- Vaccinate according to age/risk
- Evaluate recurrent meningitis for CSF leak or immune defect
Complications
- Septic shock/DIC: Especially meningococcemia
- Hearing loss: Classic pneumococcal complication
- Seizures/cerebral edema: Acute neurological complications
- Hydrocephalus/subdural empyema: Complicated infection
USMLE Step 2 CK Exam Tips
- 1Suspected bacterial meningitis = antibiotics now
- 2CT before LP only with specific risk factors
- 3Adult empiric: vancomycin + ceftriaxone; add ampicillin for Listeria risk
- 4Dexamethasone must be before/with first antibiotics
- 5HSV encephalitis = temporal lobe signs; give acyclovir
- 6Bacterial CSF = neutrophils, low glucose, high protein
- 7Meningococcal contacts need prophylaxis
practicetest your knowledge on meningitis (bacterial & viral)Apply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — neurology and beyond.
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