Meningitis

Meningitis is inflammation of the meninges (the membranes surrounding the brain and spinal cord), most commonly caused by infection. It is a medical emergency.

Etiology

The causative agent varies by age and immune status (Harrison's, p. 14669):

Category	Common Pathogens
Neonates	Group B Streptococcus, E. coli, Listeria monocytogenes
Children/Adults	Streptococcus pneumoniae, Neisseria meningitidis, H. influenzae
Elderly/Immunocompromised	L. monocytogenes, gram-negatives
Viral (Aseptic)	Enteroviruses, HSV-2, mumps, HIV
Fungal	Cryptococcus neoformans (esp. HIV patients), Candida
Tuberculous	Mycobacterium tuberculosis

Pathophysiology

Organisms reach the meninges via hematogenous spread or direct extension. Once in the subarachnoid space, bacterial components trigger a robust inflammatory cascade, leading to:

Increased intracranial pressure (ICP)
Cerebral edema
Impaired CSF resorption → hydrocephalus
Vasculitis and cortical injury

Clinical Features

The classic triad (present together in only ~44% of cases):

Fever
Nuchal rigidity (neck stiffness)
Altered mental status / headache

Additional signs:

Kernig's sign: resistance to knee extension with hip flexed
Brudzinski's sign: involuntary hip/knee flexion on neck flexion
Photophobia, phonophobia
Petechial/purpuric rash — classic for meningococcal disease (medical emergency)
Seizures, focal neurological deficits (in complicated cases)

Diagnosis

Step 1 — CT Head Before LP?

Obtain CT first if any of:

Papilledema
Focal neurological deficits
Severely altered consciousness / new-onset seizures
Immunocompromised state

Do NOT delay antibiotics waiting for CT or LP!

Step 2 — Lumbar Puncture (CSF Analysis)

Parameter	Bacterial	Viral	Tuberculous	Fungal
Appearance	Turbid/cloudy	Clear	Clear/xanthochromic	Clear/cloudy
WBC	>1000 (PMNs)	<500 (lymphs)	100–500 (lymphs)	<500 (lymphs)
Protein	↑↑ (>100 mg/dL)	Mildly ↑	↑↑	↑
Glucose	↓↓ (<40 mg/dL)	Normal	↓	↓
Opening pressure	↑↑	Normal/↑	↑	↑↑
Gram stain/Culture	Positive ~70–80%	Negative	Negative (ZN stain)	India ink/CrAg

Additional tests:

Blood cultures (×2 before antibiotics if possible)
Serum glucose (for CSF:serum ratio)
CBC, CMP, CRP, procalcitonin
PCR panels (HSV, enterovirus) on CSF
Cryptococcal antigen (CrAg) in immunocompromised

Imaging

MRI with gadolinium is the imaging modality of choice when complications are suspected:

Multi-parametric MRI showing basal meningitis with communicating hydrocephalus, periventricular white matter changes on T2/FLAIR, and diffuse leptomeningeal enhancement on gadolinium sequences — characteristic of tuberculous or cryptococcal meningitis.

Management

Empiric Antibiotic Therapy (start immediately)

Patient Group	Empiric Regimen
Adults 18–50	Ceftriaxone 2g IV q12h + Vancomycin
>50 yrs / immunocompromised	+ Ampicillin (covers Listeria)
Neonates	Ampicillin + Cefotaxime (or Gentamicin)
Penicillin allergy	Chloramphenicol or Meropenem

Adjust based on culture/sensitivity results.

Adjunctive Dexamethasone

Dexamethasone 0.15 mg/kg IV q6h × 4 days — start with or before first antibiotic dose
Proven benefit in pneumococcal meningitis (reduces mortality, neurological sequelae)
Benefit in other bacterial meningitis is less clear

Antiviral (if HSV suspected)

Acyclovir 10 mg/kg IV q8h — start empirically if encephalitis is possible

Antifungal (Cryptococcal)

Induction: Liposomal amphotericin B + Flucytosine × 2 weeks
Consolidation: Fluconazole × 8 weeks

Supportive Care

Strict neuro monitoring (GCS, pupils)
ICP management (head of bed 30°, osmotherapy if needed)
Seizure prophylaxis/treatment
Fever control, fluid balance
Isolation precautions for meningococcal disease (droplet)

Complications

Complication	Notes
Hydrocephalus	May require EVD placement
SIADH / hyponatremia	Common, monitor Na⁺ closely
Subdural empyema	Neurosurgical emergency
Cerebral venous sinus thrombosis	MRV to diagnose
Hearing loss	Especially post-pneumococcal; audiological follow-up
Cognitive impairment, seizures	Long-term sequelae
Waterhouse-Friderichsen syndrome	Adrenal hemorrhage in meningococcemia
Death	Bacterial meningitis mortality ~20–30% without treatment

Prophylaxis

Meningococcal contacts: Rifampin 600 mg PO q12h × 2 days, or Ciprofloxacin single dose, or Ceftriaxone IM single dose
Vaccination: MenACWY, MenB vaccines; PCV13/PPSV23 for pneumococcal; Hib vaccine

Prognosis

Bacterial meningitis carries significant morbidity/mortality. Prognosis worsens with:

Delayed treatment
Extremes of age
Impaired consciousness at presentation
Pneumococcal etiology
Gram-negative organisms (Harrison's, p. 14669)

Viral meningitis is generally self-limiting with good outcomes. Tuberculous and fungal meningitis require prolonged therapy and carry higher morbidity.

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