Meningitis

Meningitis – High-Yield Study Guide for Medical Students

Definition

Meningitis is an acute or chronic inflammation of the meninges (pia mater, arachnoid mater, and dura mater), usually involving the subarachnoid space and cerebrospinal fluid (CSF). It is classically divided into:

• Acute bacterial meningitis: Rapidly progressive, purulent infection with high morbidity and mortality if not treated promptly.
• Viral (aseptic) meningitis: Typically self-limited, often caused by enteroviruses.
• Chronic meningitis: Subacute to chronic course (>4 weeks) due to organisms such as Mycobacterium tuberculosis or fungi.

Epidemiology

Meningitis remains a major cause of neurological morbidity and mortality worldwide, particularly in neonates, young children, older adults, and immunocompromised patients.1,5,6

• Age-specific pathogens:
  • Neonates: Group B Streptococcus (GBS, Streptococcus agalactiae), E. coli, Listeria monocytogenes.6
  • Children & young adults: Neisseria meningitidis, Streptococcus pneumoniae.
  • Older adults (>50 years) and immunocompromised: S. pneumoniae, Listeria, gram‑negative bacilli.
• Risk factors: extremes of age, functional or anatomic asplenia, complement deficiency, CSF leaks, neurosurgical procedures, close living quarters (e.g. dormitories), HIV infection, and other forms of immunosuppression.5,6
• Global burden: Higher incidence in low‑resource settings and in the “meningitis belt” of sub‑Saharan Africa; HIV-associated meningitis is an important cause of neurocognitive morbidity.5

Pathophysiology

Meningitis pathophysiology reflects the interaction between invading pathogens and the host immune response within the CSF and meninges.1,5,6

• Entry and invasion:
  • Most bacterial meningitis begins with nasopharyngeal colonization, mucosal invasion, and hematogenous spread.
  • Pathogens cross the blood–brain barrier (BBB) or blood–CSF barrier, often via choroid plexus or meningeal capillaries.
  • Direct extension from contiguous foci (e.g. sinusitis, otitis media, skull fracture) or neurosurgical procedures is also possible.1
• Inflammatory cascade:
  • Bacterial cell wall components (e.g. lipoteichoic acid, lipooligosaccharide) trigger cytokine release (TNF‑α, IL‑1β, IL‑6) in the subarachnoid space.
  • This leads to increased BBB permeability, vasogenic edema, leukocyte influx, and impaired CSF outflow.
  • Resultant intracranial hypertension, reduced cerebral perfusion, and neuronal injury underlie many clinical manifestations.1
• Chronic/HIV-associated meningitis:
  • Organisms such as M. tuberculosis and cryptococci produce a granulomatous or basilar meningeal exudate, leading to cranial neuropathies, hydrocephalus, and vasculitic infarcts.
  • In HIV-associated meningitis, ongoing inflammation in and around the brain contributes to cognitive dysfunction, behavioral changes, and psychiatric comorbidity.5

Clinical Presentation

Presentation varies with age, pathogen, and host immune status, but certain patterns are high-yield for exams and clinical practice.4,5

Classic triad (older children and adults)

• Fever
• Neck stiffness (nuchal rigidity)
• Altered mental status

The full triad is present in a minority, but nearly all patients have at least two of the following: headache, fever, neck stiffness, altered consciousness.

Other common features

• Headache: Diffuse, severe, often with photophobia and phonophobia.
• Nausea and vomiting.
• Seizures: Focal or generalized; more common with bacterial or tuberculous meningitis.
• Focal neurological deficits: Cranial nerve palsies, hemiparesis, ataxia, particularly in tuberculous or fungal disease.5
• Rash: Petechial or purpuric rash in meningococcal meningitis; suggests meningococcemia and possible septic shock.

Signs of meningeal irritation

• Kernig sign: Pain/resistance on knee extension with hip flexed at 90°.
• Brudzinski sign: Involuntary hip and knee flexion when neck is passively flexed.
• These signs are classic but neither highly sensitive nor specific; absence does not exclude meningitis.

Presentation in infants and neonates

• Non-specific signs: poor feeding, irritability, lethargy, temperature instability, apnea.
• Bulging fontanelle, high-pitched cry, seizures.
• Neck stiffness may be absent; have a low threshold for evaluation in febrile infants.4

Diagnosis

Meningitis is a clinical and CSF diagnosis; rapid recognition and early empiric therapy are critical.4,5

Initial assessment

• Stabilization: Assess airway, breathing, circulation, and neurologic status (GCS).
• History: Time course, recent infections (sinusitis, otitis), travel, sick contacts, vaccination status, immunosuppression, neurosurgical procedures, head trauma.
• Examination: Meningeal signs, focal neurological deficits, rash, papilledema, signs of raised intracranial pressure (ICP).

Laboratory workup

• Blood tests:
  • Complete blood count, CRP, electrolytes, renal and liver function.
  • Blood cultures x2 prior to antibiotics when feasible, but do not delay treatment if unstable.4
• Neuroimaging:
  • Head CT (or MRI) before lumbar puncture (LP) in patients with focal deficits, new-onset seizures, papilledema, severely depressed consciousness, or significant immunosuppression.
  • Goal is to assess for mass lesion or marked mass effect that could increase risk of herniation with LP.4

Lumbar puncture and CSF analysis

LP with CSF analysis is the cornerstone of meningitis diagnosis and pathogen identification.4,5

• Opening pressure: Elevated in bacterial and tuberculous meningitis.
• Cell count and differential:
  • Bacterial: High WBC (often >1000/µL) with neutrophilic predominance.
  • Viral: Moderate WBC elevation (typically <500/µL) with lymphocytic predominance.
  • TB/fungal: Lymphocytic pleocytosis, may be moderate to high.
• Protein:
  • Markedly elevated in bacterial and TB/fungal meningitis.
  • Mild to moderate elevation in viral meningitis.
• Glucose (CSF:blood ratio):
  • Low in bacterial and TB/fungal (CSF:serum glucose ratio <0.4 is concerning).
  • Usually normal in viral meningitis.
• Gram stain and culture: Key for bacterial meningitis; Gram stain sensitivity increases with CSF bacterial load.
• Additional tests:
  • CSF PCR for common viruses (enteroviruses, HSV) and bacterial pathogens.
  • Acid-fast stain, TB PCR, and culture for TB meningitis.
  • India ink, cryptococcal antigen in HIV or immunocompromised patients.5

Management

Management priorities: rapid empiric antimicrobial therapy, adjunctive corticosteroids in selected cases, supportive care, and management of complications.4,5

General principles

• Time-critical: Once meningitis is suspected, obtain blood cultures and start empiric IV antibiotics without delaying for imaging or LP in unstable or high-risk patients.
• Empiric regimen is age- and risk-factor specific; adjust once pathogen and susceptibilities are known.
• Admit to monitored setting; consider ICU for patients with altered consciousness, seizures, or hemodynamic instability.

Empiric antibiotic therapy (examples – adapt to local guidelines and resistance patterns)

• Neonates (0–28 days):
  • Ampicillin (for Listeria and GBS) + a third-generation cephalosporin (e.g. cefotaxime) or an aminoglycoside.
• Infants & children:
  • Third-generation cephalosporin (e.g. ceftriaxone or cefotaxime) + vancomycin (for penicillin-resistant pneumococci).
• Adults <50 years:
  • Ceftriaxone (or cefotaxime) + vancomycin.
• Adults ≥50 years or immunocompromised:
  • Ceftriaxone (or cefotaxime) + vancomycin + ampicillin (for Listeria coverage).
• Post-neurosurgical / CSF shunt infections:
  • Vancomycin + anti-pseudomonal agent (e.g. cefepime, meropenem), guided by local patterns.

Adjunctive corticosteroids

• Dexamethasone given just before or with the first dose of antibiotics reduces inflammation-mediated neurologic sequelae in some bacterial meningitis, particularly pneumococcal disease.1
• Benefits include reduced hearing loss and possibly decreased mortality; efficacy varies by pathogen and setting.
• Continue only if a steroid-responsive pathogen (e.g. S. pneumoniae) is confirmed.

Supportive and complication management

• ICP management: Elevate head of bed, maintain adequate oxygenation and perfusion; consider hyperosmolar therapy or CSF diversion in severe cases.
• Seizures: Treat with benzodiazepines acutely and start appropriate antiepileptic drugs if recurrent.
• Septic shock / meningococcemia: Aggressive fluid resuscitation, vasopressors as needed, close hemodynamic monitoring.
• Hydrocephalus: Particularly in TB or cryptococcal meningitis; may require ventriculostomy or shunt.

Special situations

• HIV-associated meningitis:
  • Consider cryptococcal, TB, and other opportunistic pathogens.
  • Management includes pathogen-directed therapy and careful timing of antiretroviral initiation to limit immune reconstitution inflammatory syndrome.
  • Psychiatric and neurocognitive sequelae are common and may be exacerbated by HIV-related stigma.5
• Neonatal GBS meningitis:
  • GBS is a leading cause of neonatal meningitis and long-term neurological disability.6
  • Maternal intrapartum prophylaxis reduces early-onset disease, but late-onset meningitis can still occur.

Prevention

• Vaccination:
  • Haemophilus influenzae type b (Hib) vaccine virtually eliminated Hib meningitis where widely used.
  • Pneumococcal conjugate vaccines reduce invasive pneumococcal disease, including meningitis.
  • Meningococcal vaccines (conjugate and serogroup B) are recommended for adolescents and other high-risk groups.
• Chemoprophylaxis:
  • Close contacts of meningococcal meningitis receive rifampin, ciprofloxacin, or ceftriaxone as prophylaxis.
• Perinatal screening:
  • Screening pregnant women for GBS colonization and intrapartum antibiotic prophylaxis reduce neonatal GBS sepsis and meningitis.6
• Infection control and education:
  • In low-resource settings, simulation-based education for trainees can improve preparedness for managing life-threatening infections including meningitis.3

Key Clinical Pearls

• Do not wait for LP to start antibiotics if meningitis is strongly suspected and the patient is unstable or requires urgent imaging first.
• Age, immune status, and clinical context drive your empiric antibiotic choice and your differential diagnosis.
• CSF profile is high-yield for exams: neutrophilic pleocytosis + low glucose + high protein suggests bacterial; lymphocytic + normal glucose suggests viral; lymphocytic + very high protein + low glucose suggests TB or fungal.
• Dexamethasone is most beneficial in pneumococcal meningitis and must be given before or with the first antibiotic dose.1
• Consider TB, cryptococcal, or carcinomatous meningitis in subacute or chronic presentations, especially with cranial neuropathies and in immunocompromised hosts.5
• Neonates and infants may present without classic signs; unexplained sepsis or irritability should prompt consideration of meningitis.4,6
• Meningitis can leave significant neurocognitive and mental health sequelae, especially in HIV-associated disease; long-term follow-up is important.5

Learning and Simulation in Meningitis Care

• Simulation-based training using clinical decision-making cases improves residents’ ability to rapidly recognize and treat febrile infants with possible meningitis.4
• High-fidelity neurosurgical and skull base models can aid in understanding meningeal anatomy and complications related to meningeal pathology.1,2
• Global health simulation curricula prepare trainees for meningitis management in low-resource environments, where diagnostic and therapeutic options may be limited.3

Summary

Meningitis is a neurologic emergency characterized by inflammation of the meninges and CSF. Rapid recognition of clinical features, prompt LP (when safe), targeted CSF analysis, and immediate empiric antimicrobial therapy are central to favorable outcomes. Prevention through vaccination, chemoprophylaxis, and perinatal screening has significantly reduced disease burden but gaps remain, particularly in low-resource and immunocompromised populations.1,3,5,6