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I now have comprehensive, exam-quality content from Harrison's and Tintinalli's. Let me compose the full short note answer.
MENINGITIS - Exam Short Note
Definition
Meningitis is inflammation of the meninges (pia, arachnoid, and dura mater) and the subarachnoid CSF, caused by infectious or non-infectious agents.
Classification
| Type | Common Causes |
|---|---|
| Acute Bacterial | S. pneumoniae, N. meningitidis, H. influenzae type b, Group B Streptococcus (neonates), L. monocytogenes |
| Viral (Aseptic) | Enteroviruses (echovirus, Coxsackie - 80%), HSV-2, HIV, mumps, VZV |
| Subacute/Chronic | M. tuberculosis (most common chronic cause), Cryptococcus neoformans, fungal species |
| Neonatal | Group B Streptococcus, E. coli, L. monocytogenes |
Age-specific organisms:
- <1 month: GBS, E. coli, Listeria
- 1 month - 50 years: N. meningitidis, S. pneumoniae
- >50 years / immunocompromised: S. pneumoniae, gram-negative rods, Listeria
- Post-neurosurgical / shunt: S. aureus, coagulase-negative staphylococci
Pathophysiology
- Nasopharyngeal colonization by bacteria (e.g., S. pneumoniae, N. meningitidis)
- Invasion across epithelial tight junctions into bloodstream
- Bacteria survive via polysaccharide capsule (resist phagocytosis + complement)
- Reach choroid plexus → enter CSF
- Rapid multiplication in CSF (poor complement/IgG levels - normal CSF has few WBCs)
- Bacterial cell wall components trigger cytokine-mediated inflammatory response
- Increased vascular permeability → cerebral edema → raised ICP → tissue damage
(Source: Harrison's Principles of Internal Medicine 22E, p. 1163-1164)
Clinical Features
Classic Triad:
Fever + Headache + Neck stiffness (nuchal rigidity)
Additional features:
- Photophobia, phonophobia
- Nausea, vomiting
- Altered consciousness / confusion
- Seizures
- Petechial/purpuric rash (classic for N. meningitidis)
Meningeal Signs:
- Kernig's sign - Patient supine; flex thigh on abdomen + flex knee; passive extension of knee causes pain/resistance
- Brudzinski's sign - Passive neck flexion causes involuntary flexion of hips and knees
- Bulging fontanelle (in neonates/infants)
Neonatal presentation (non-specific):
Lethargy, poor feeding, hypothermia or fever, bulging fontanelle, grunting, respiratory distress, seizures
Diagnosis
Lumbar Puncture - CSF Analysis (KEY EXAM TABLE)
| Parameter | Normal | Bacterial | Viral | TB/Fungal |
|---|---|---|---|---|
| Appearance | Clear | Turbid/cloudy | Clear | Opalescent |
| Opening pressure | <180 mmH₂O | Raised (>180) | Normal/mildly raised | Raised |
| WBC count | <5 cells/μL | >100 (PMN predominance) | 10-500 (lymphocyte predominance) | 10-500 (lymphocyte predominance) |
| Glucose | 50-80 mg/dL (CSF:serum >0.6) | LOW (<40 mg/dL; CSF:serum <0.4) | Normal | LOW |
| Protein | 15-45 mg/dL | HIGH (>45 mg/dL; often >100) | Mildly elevated | HIGH |
| Gram stain | Negative | Positive in >60% | Negative | AFB stain |
| Culture | Negative | Positive >70% | Viral culture | Culture / PCR |
From Harrison's: Classic CSF abnormalities in bacterial meningitis: (1) PMN leukocytosis >100 cells/μL in 90%, (2) glucose <40 mg/dL and/or CSF:serum ratio <0.4 in ~60%, (3) protein >45 mg/dL in 90%, (4) opening pressure >180 mmH₂O in 90%.
When to CT BEFORE LP:
- Focal neurologic deficits
- Papilledema
- Impaired consciousness
- History of recent head trauma / immunocompromised
- (Do NOT delay antibiotics for imaging)
Bacterial Meningitis Score (BMS) - pediatric:
- CSF Gram stain positive (2 points)
- CSF protein >80 mg/dL (1 point)
- Blood absolute neutrophil count ≥10,000/mm³ (1 point)
- Seizure at or before presentation (1 point)
- CSF WBC ≥100 cells/μL (1 point)
Treatment
Empirical Antimicrobial Therapy (community-acquired, adults/older children):
| Regimen Component | Drug |
|---|---|
| 3rd/4th gen cephalosporin | Ceftriaxone 2g IV q12h OR Cefotaxime |
| For resistant S. pneumoniae | + Vancomycin |
| Cover Listeria (if <3 months, >55 yrs, immunocompromised, pregnancy) | + Ampicillin |
| HSV encephalitis in differential | + Acyclovir |
| Anaerobes (otitis/sinusitis/mastoiditis) | + Metronidazole |
| Hospital-acquired / post-neurosurgical | Vancomycin + Cefotaxime or Meropenem |
Goal: antibiotics within 60 minutes of emergency room arrival (Harrison's 22E, p. 1164)
Adjunctive Dexamethasone:
- 0.15 mg/kg IV every 6 hours for 4 days (up to 10 mg per dose)
- Give before or with the first antibiotic dose (ideally 20 minutes before)
- Reduces mortality in pneumococcal meningitis
- Reduces hearing loss (especially in H. influenzae meningitis)
- Mechanism: reduces CNS inflammation and cytokine storm
Neonatal empirical therapy:
- Ampicillin + Cefotaxime (or Gentamicin) - covers GBS, E. coli, Listeria
Complications
- Sensorineural hearing loss (most common neurologic sequela; predicted by S. pneumoniae etiology and low CSF glucose)
- Hydrocephalus
- Cerebral edema / raised ICP
- Seizures
- Waterhouse-Friderichsen syndrome (bilateral adrenal hemorrhage in meningococcemia)
- Subdural effusion / empyema
- Cognitive impairment, learning disabilities
- Death - mortality <10% with appropriate antibiotics
Predictors of mortality: coma, seizures, shock, respiratory distress, neutropenia, high CSF protein
Prevention
- Hib vaccine (dramatically reduced H. influenzae meningitis in children)
- Pneumococcal vaccine (PCV13 / PPSV23)
- Tetravalent meningococcal vaccine (serogroups A, C, W-135, Y)
- MenB vaccine (serogroup B, now required for many university students)
Sources: Harrison's Principles of Internal Medicine 22E, p. 1163-1165 | Tintinalli's Emergency Medicine, p. 795 | Bradley and Daroff's Neurology in Clinical Practice, p. 1698
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