L61: Pulmonary Infections Flashcards
Bacterial infection: Pneumonia
Acute suppurative inflammation
- Early stage: Congestion + oedema
- Intermediate stage: Consolidation (air space filling up)
- alveoli full of exudates: neutrophil, fibrinous protein
- firm, solid, red lung
- radiopague
- Bronchopneumonia:
—> Patchy, bilateral, lower lobes, multifocal
—> around terminal bronchioles
—> confluent in severe cases
- Lobar pneumonia: Diffuse involving whole lobe
—> Diffuse, solid, liver-like
—> S. pneumoniae
—> virulent: spread quickly throughout lung - Late stage: Resolution / complication
- neutrophil degenerate
- macrophage increase to clear up debris
- less congested lung, red to greyish
- resolution / residual damage
Symptoms of Pneumonia
Systemic:
- fever
- malaise
Chest:
- purulent, greenish-yellow sputum
- dyspnea
- reduced air entry
- bronchial breath sounds
- crepitations
Diagnosis of pneumonia
Definitive diagnosis: Culture of respiratory tract specimen
- history (age, underlying illness, travel, animal contact, defect in resistance)
- physical examination (pulse-temperature deficit)
- X-ray: patchy, diffuse white shadows
- Sputum: macroscopic, colour, amount, consistency, rusty (S. pneumoniae), currant-jelly (Klebsiella pneumoniae)
- blood gas, blood count
- Bronchoalveolar lavage (BAL) + fibreoptic bronchoscopy
- pleural fluid aspiration, culture
- biopsy
- PCR: virus, atypical pathogen
- Serology: atypical antigen
- Viral antigen detection: immunofluorescent
- urine antigen detection: S. pneumoniae, Legionella pneumophila
Predisposing factors to pneumonia
- Virulent organism (S. pneumoniae)
- Immunocompromised (DM)
- Impaired airway clearance (smoking, loss of cough reflex)
- Lung congestion and oedema (cystic fibrosis)
- Poor health
- Secondary to viral bronchitis
Outcome of pneumonia
- Total resolution
- Severe:
- destruction of parenchyma
- fibrosis
- abscess: lung abscess, empyema thoracis
- spreading:
—> adjacent (pleuritis, pericarditis, empyema thoracis)
—> distant (meningitis, arthritis)
Viral and mycoplasma (NOT mycobacterium) infections
Intracellular organisms
—> infect epithelium and interstitium
—> Interstitial pneumonitis
—> Interstitium infiltrated by lymphocyte, macrophage, plasma cells
—> mild: cough without sputum, self-limiting
—> severe: Diffuse alveolar damage (DAD), alveolocapillary block, impaired oxygen diffusion, hypoxia, SOB
Mycobacterium tuberculosis
- Chronic inflammation (due to difficulty in eradicating the bacteria completely, persist in macrophage)
- Infect lung parenchyma + draining lymph nodes
- Primary infection (no previous immunity): heal with small scar in lung/lymph nodes
- Secondary infection (sensitised T cells): Type 4 hypersensitivity reaction —> granulomatous inflammation —> mycobacterial granulomas
- Miliary TB: wide systemic spread —> multiple small granuloma
Describe Mycobacterial granuloma
Caseous necrosis surrounded by
- Epitheloid histiocyte
- Langhans giant cells
- Lymphocytes
- Fibroblast
Gross appearance of pulmonary tuberculosis
- Caseous necrosis
- Cavitation
- Calcification
- Fibrosis
Fungal infections
- Aspergillosis
- pre-existing saprophytic growth—> form colonies without tissue invasion
- immunocompromised —> tissue invasion
- hyphae growing through arterial wall —> fatal pulmonary haemorrhage - Pneumocystis jirovecii
- fatal in AIDS patient
- diagnosis: BAL
- alveolar casts: frothy sputum, ball-like exudates (stained by Grocott stain)
Bronchiectasis
Dilatation of bronchi and large bronchioles
- permanent and irreversible
- diffuse / regional (often lower lobes)
- copious foul-smelling sputum induced by postural change
- recurrent / chronic lung infection
- abscess
- chronic hypoxia / pulmonary hypertension
***Vicious cycle of obstruction and infection
- Chronic infection (due to TB, complications of viral bronchitis, complications of previous bronchopneumonia)
—> necrosis, destruction and obstruction of bronchial wall
—> negative intrathoracic pressure pull on weakened wall
—> dilatation
—> impaired mucus and pus drainage
—> more infection - Bronchial obstruction
- Lumen: mucus, sputum, exudate, foreign body, impaired ciliary clearncae
- Mural: tumour, scarring of bronchial wall
- Compression: enlarged lymph nodes
—> leads to accumulation of secretions
—> chronic bacterial infection
—> Necrosis, weakening, scarring of bronchial wall
—> accumulation of pus and mucus
—> obstruction
—> more infection
Bronchiectasis vs Emphysema
Bronchiectasis: occur in bronchi
Emphysema: occur in alveoli
