Classify meningitis describe etiology clinical features investigation management of pneunomia 15 mark question general medicine
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MENINGITIS: Classification, and PNEUMONIA: Etiology, Clinical Features, Investigations, Management
PART A: CLASSIFICATION OF MENINGITIS
Meningitis is inflammation of the meninges (pia, arachnoid, and dura mater) and the subarachnoid space. It is classified based on the causative agent, time course, and clinical setting.
I. Based on Etiology
A. Bacterial (Purulent) Meningitis
| Setting | Organisms |
|---|---|
| Community-acquired (age <50, no risk factors) | Streptococcus pneumoniae, Neisseria meningitidis |
| Age >50 / immunocompromised | Above + Listeria monocytogenes |
| Neonates | Group B Streptococcus, E. coli, Listeria |
| Post-sinusitis / otitis media | Anaerobes + pneumococcus |
| Neurosurgical / post-traumatic | Staphylococcus aureus, gram-negative bacilli |
- S. pneumoniae and N. meningitidis colonize the nasopharyngeal mucosa, providing a route of entry. Listeria is typically acquired via contaminated food.
B. Viral (Aseptic) Meningitis
- Most common overall. Caused by enteroviruses (most frequent), HSV-2, mumps, HIV, arboviruses (West Nile, Japanese encephalitis).
- CSF shows lymphocytic pleocytosis with normal glucose.
C. Tuberculous (TB) Meningitis
- Caused by Mycobacterium tuberculosis - the leading cause of chronic meningitis worldwide.
- Subacute onset, basilar involvement, mononuclear pleocytosis, markedly low CSF glucose.
D. Fungal Meningitis
- Cryptococcus neoformans (most common, especially in HIV), Coccidioides, Histoplasma, Candida, Aspergillus.
- CSF resembles TB meningitis (mononuclear pleocytosis, low-moderate glucose), except Aspergillus often causes neutrophil predominance.
E. Parasitic Meningitis
- Naegleria fowleri (primary amoebic), Angiostrongylus cantonensis (eosinophilic), Taenia solium (neurocysticercosis), Plasmodium falciparum (cerebral malaria).
F. Non-infectious (Aseptic) Meningitis
- Drug-induced (NSAIDs, trimethoprim, IV immunoglobulin), autoimmune (SLE, sarcoidosis), neoplastic (carcinomatous meningitis).
II. Based on Time Course
| Type | Duration | Common Causes |
|---|---|---|
| Acute | Hours to days | Bacterial, viral |
| Subacute | Days to weeks | TB, viral (HIV), fungal |
| Chronic | >4 weeks | TB (M. tuberculosis is the leading cause globally), fungal, syphilitic, carcinomatous |
III. Based on CSF Profile
| Type | Cells | Protein | Glucose | Organisms |
|---|---|---|---|---|
| Bacterial | PMN predominance (>1000/mm³) | High (>100 mg/dL) | Low (<45 mg/dL or <40% blood glucose) | Gram stain/culture positive |
| Viral | Lymphocytes (100-500/mm³) | Mildly elevated | Normal | Negative culture; PCR positive |
| TB | Lymphocytes (100-500/mm³) | Very high | Low (markedly) | AFB stain/culture; PCR |
| Fungal | Mononuclear (low count) | Elevated | Mildly low | India ink; cryptococcal Ag |
PART B: PNEUMONIA - Etiology, Clinical Features, Investigations, Management
Definition
Pneumonia is an acute infection of the lung parenchyma causing inflammation of the alveoli and/or interstitium, characterized by fever, cough, sputum production, and a pulmonary infiltrate on imaging.
Classification (Clinically Important)
- Community-Acquired Pneumonia (CAP) - acquired outside hospital
- Hospital-Acquired (Nosocomial) Pneumonia (HAP) - onset >48 hours after admission
- Ventilator-Associated Pneumonia (VAP) - in mechanically ventilated patients
- Aspiration Pneumonia - following aspiration of oropharyngeal/gastric contents
- Immunocompromised Host Pneumonia - opportunistic infections
ETIOLOGY
The cause varies by clinical setting. In over 50% of cases, no specific pathogen is confirmed. Key organisms:
Typical organisms (accounts for ~25-30% of CAP):
- Streptococcus pneumoniae - most common bacterial cause of CAP
- Haemophilus influenzae - especially in smokers and COPD
- Staphylococcus aureus - post-influenza, IV drug users
- Gram-negative bacilli (Klebsiella, Pseudomonas, E. coli) - aspiration, HAP, immunocompromised
Atypical organisms (~10-20% of CAP):
- Mycoplasma pneumoniae - young adults, "walking pneumonia"
- Chlamydophila pneumoniae - young adults
- Legionella pneumophila - water systems, air conditioning, smokers, elderly; can cause severe CAP
- Viruses - Influenza, RSV, SARS-CoV-2, adenovirus (~20-30% of CAP)
Special exposure associations:
| Exposure | Organism |
|---|---|
| Pigeons / bird droppings | Cryptococcus neoformans |
| Psittacine (parrots) | Chlamydia psittaci |
| Farm animals | Coxiella burnetii (Q fever) |
| Rabbits | Francisella tularensis |
| SW United States | Coccidioides immitis |
| Bat/bird guano (Mississippi) | Histoplasma capsulatum |
| Aspiration / poor dentition | Anaerobes, Candida |
| Influenza season | Influenza + secondary S. aureus, S. pneumoniae |
Risk factors: Male sex, smoking, age >65, alcohol use disorder, malnutrition, COPD, diabetes, immunosuppression, neurological disease impairing gag reflex, opioid use, proton pump inhibitors, crowded living conditions.
CLINICAL FEATURES
Symptoms:
- Fever with chills (often abrupt onset in pneumococcal pneumonia)
- Productive cough (rust-coloured sputum in pneumococcal; currant-jelly in Klebsiella)
- Pleuritic chest pain (sharp, worsened by breathing)
- Dyspnoea and tachypnoea
- Myalgia, headache, malaise (more prominent in atypical pneumonia)
- Haemoptysis (in severe or necrotising pneumonia)
- Confusion / altered mental status (especially in elderly - may be presenting symptom)
Signs:
- Fever (temperature >38°C), tachycardia (>100 bpm), tachypnoea (>20/min)
- Hypoxaemia (SpO₂ <90% in severe cases)
- Lobar/bronchopneumonia signs on examination:
- Increased vocal fremitus / tactile vocal fremitus
- Dull percussion note
- Bronchial breath sounds
- Coarse crepitations (crackles)
- Pleural rub (if pleuritis present)
- Signs of complications: cyanosis, shock (severe sepsis), empyema (stony dull, absent breath sounds)
Atypical features (Mycoplasma, Chlamydia, Legionella, viruses):
- Gradual onset, dry cough, prominent extrapulmonary features
- Legionella: diarrhoea, hyponatraemia, elevated liver enzymes, haematuria; responds to macrolides/fluoroquinolones
INVESTIGATIONS
A. Confirm Diagnosis
-
Chest X-ray (CXR) - essential first investigation
- Lobar consolidation (pneumococcal), patchy bronchopneumonia (Staphylococcal/Klebsiella), interstitial infiltrates (atypical), cavitation (Klebsiella, Staphylococcal, TB)
- Pleural effusion if parapneumonic effusion or empyema
-
High-Resolution CT Chest - when CXR inconclusive; better characterisation
B. Blood Tests
- CBC - leukocytosis (neutrophilia in bacterial); leucopenia (severe sepsis, viral)
- Inflammatory markers - elevated CRP, ESR, procalcitonin (procalcitonin better for bacterial vs. viral)
- Serum electrolytes, urea, creatinine - hyponatraemia (Legionella), renal function (CRB-65/PSI scoring)
- LFTs - elevated in Legionella
- ABG / pulse oximetry - assess severity, hypoxaemia, respiratory failure
- Blood cultures (2 sets) - before antibiotics; positive in ~15-25% of hospitalised CAP
C. Microbiological
- Sputum Gram stain and culture - quality sample required (>25 PMN, <10 squamous cells per LPF)
- Urinary antigen tests - Streptococcus pneumoniae (rapid, sensitive), Legionella pneumophila serogroup 1
- Nasopharyngeal swab / PCR - viral panel (Influenza, SARS-CoV-2, RSV)
- Serology - Mycoplasma, Chlamydia, Coxiella (acute and convalescent titres; 4-fold rise)
- Bronchoscopy with BAL - in ICU patients, immunocompromised, or non-responding pneumonia
D. Severity Scoring
- CURB-65 score (Confusion, Urea >7 mmol/L, RR ≥30, BP systolic <90 or diastolic ≤60, age ≥65):
- 0-1: Outpatient; 2: Consider hospitalisation; 3-5: Hospitalise ± ICU
- PSI (Pneumonia Severity Index): Class I-II: outpatient; III: observation; IV-V: hospitalise
MANAGEMENT
General Measures
- Assess severity (CURB-65 / PSI) to determine site of care
- Supplemental oxygen to maintain SpO₂ >94% (88-92% in COPD)
- IV fluids for dehydration / haemodynamic support
- Analgesics for pleuritic pain
- DVT prophylaxis in hospitalised patients
- Monitor vitals and SpO₂; daily review
Antibiotic Therapy (Empirical)
Empirical treatment begins before pathogen identification because early antibiotics improve outcomes. Treatment is narrowed once microbiological results are available.
1. Mild CAP (Outpatient / CURB-65 score 0-1):
- Amoxicillin 500 mg TDS for 5 days (first choice)
- OR Doxycycline 100 mg BD (if penicillin allergy or atypical suspected)
- OR Azithromycin 500 mg OD x 5 days
2. Moderate CAP (Hospitalised, non-ICU):
- Beta-lactam (Co-amoxiclav or Ceftriaxone 2 g IV OD) + Macrolide (Azithromycin or Clarithromycin)
- OR Respiratory Fluoroquinolone monotherapy (Levofloxacin 500-750 mg OD, or Moxifloxacin 400 mg OD)
- Duration: 5-7 days
3. Severe CAP (ICU):
- Ceftriaxone 2 g IV OD + Azithromycin IV (or Levofloxacin)
- If Pseudomonas risk (bronchiectasis, CF): Piperacillin-tazobactam or Cefepime + Ciprofloxacin/Levofloxacin
- If MRSA risk (post-influenza, cavitating): add Vancomycin or Linezolid
4. Aspiration Pneumonia:
- Co-amoxiclav or Clindamycin + Cephalosporin (to cover anaerobes)
5. HAP / VAP:
- Broad-spectrum: Piperacillin-tazobactam + Vancomycin (if MRSA risk)
6. Specific agents:
- Influenza pneumonia: Oseltamivir (Tamiflu) within 48 hours
- Legionella: Azithromycin or Levofloxacin (macrolides/fluoroquinolones)
- TB: Standard HRZE regimen (Isoniazid, Rifampicin, Pyrazinamide, Ethambutol)
- PCP (P. jirovecii in HIV): Trimethoprim-sulfamethoxazole high dose
Management of Complications
- Parapneumonic effusion / Empyema: chest drain; surgical decortication if loculated
- Respiratory failure: high-flow O₂, non-invasive ventilation (CPAP/BiPAP), mechanical ventilation
- Septic shock: IV fluids, vasopressors (noradrenaline), source control
- Lung abscess: prolonged antibiotics (4-6 weeks); percutaneous or surgical drainage
- Cardiac complications (AF, acute MI, HF exacerbation): ~20-25% of hospitalised cases
Prevention
- Pneumococcal vaccine (PCV13/PPSV23): recommended in >65 years, chronic illness, immunosuppressed
- Influenza vaccine annually
- COVID-19 vaccine
- Smoking cessation
- Good oral/dental hygiene
Summary Table: CSF Findings in Meningitis
| Feature | Normal | Bacterial | Viral | TB | Fungal |
|---|---|---|---|---|---|
| Appearance | Clear | Turbid/purulent | Clear | Clear/fibrin web | Clear/turbid |
| Cells | 0-5 | >1000 PMNs | 10-500 lymphocytes | 100-500 lymphocytes | 10-200 mononuclear |
| Protein | <45 mg/dL | >100 mg/dL | Mildly elevated | Very high | Elevated |
| Glucose | 60-80 mg/dL | Very low (<40) | Normal | Low | Moderately low |
| Special tests | - | Gram stain, culture, PCR | Viral PCR | AFB, PCR, ADA | India ink, CrAg |
Sources:
- Bradley and Daroff's Neurology in Clinical Practice (Chapter 79: Bacterial CNS Infections)
- Goldman-Cecil Medicine (Chapter 85: Pneumonia)
- Murray & Nadel's Textbook of Respiratory Medicine
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