Infections In the Lung

Question 1

What are the clinical features of pneumonia?

Answer 1

• fever and chills
• unrelenting cough
• sputum production (purulent/yellow)
• chest pain (if pleura inflamed)
• impaired gas exchange resulting in SOB/dyspnoea and tachypnoea, and hypoxemia

Question 2

Hospital patients are more susceptible to what type of pneumonia-causing agents?

Answer 2

gram negative bacteria (e.g. pseudomonas)

Question 3

Immunocompromised hosts are more likely to get pneumonia caused by

Answer 3

fungi and protozoa (e.g pneumocystis jirovecii)

Question 4

What are the 4 routes of infectious pathogens into the lungs?

Answer 4

• inhalation of pathogens in air droplets
• aspiration of infected secretions from URT
• aspiration of infected particles
  
  • gastric contents, food, drink, foreign bodies
• haematogenous spread (via blood)

Question 5

What are the 3 main causes of pneumonia?

Answer 5

• URT flora
  
  • S. pneumoniae, H. influenzae, S. aureus
• enteric saprophytes, by contaminaiting airways or blood stream
  
  • E. coli, Pseudomonas
• extraneous pathogens
  
  • Legionella pneumophilia, TB

Question 6

What are the 2 patterns of infective pneumonia?

Answer 6

• alveolar inflammation
  
  • neutrophils in the alveolar spaces = consolidation
    
    • Strep, Staph Haemophilus, G-ves
• interstitial inflammation
  
  • lymphocytes, macrophages, sometimes plasma cells in the connective tissue septa between the alveoli (interstitium)
    
    • viruses, atypical pneumonia viruses (mycoplasma pneumoniae)

Question 7

What are the two types of alveolar pneumonia?

Answer 7

• bronchopneumonia
  
  • consolidation is patchy, multi-focal; very often bilateral (more than 1 lobe)
• lobar pneumonia
  
  • involves an entire lobe and often inflammation of the adjacent pleura

Question 8

What is the most common cause of lobar pneumonia?

Answer 8

S. pneumoniae (90%)

and H. influenzae

Question 9

How is lobar pneumonia acquired?

Answer 9

• community acquired in adults 20-50
• commonly following viral URTI

Question 10

What is the clinical presentation of lobar pneumonia?

Answer 10

• abrupt onset
• fever & chills
• rasied WBC
• cough
• pleuritic chest pain
• haemoptisis
• G+ diplococci in sputum
• bacteraemia

Question 11

What are the 4 stages of lobar pneumonia?

Answer 11

• congestion of alveolar capillaries
  
  • alveolar spaces filled with proteinaceous exudate containing G+ diplococci (Strep)
• red hepatization (consolidation)
  
  • haemorrhage into air spaces
• grey hepatization
  
  • fibrin, neutrophils, macrophages in alveolar spaces
• resolution

Question 12

What is a cute bronchopneumonia?

Answer 12

• most common pattern of bacterial pneumonia
• patchy consolidation, often multi-focal and involving more than one lobe or lung
• centered on bronchioles, spreads into surrounding alveolar spaces

Question 13

Acute bronchopneumonia is common in

Answer 13

• extremes of life
• secondary to pre-existing chronic disease
  
  • COPD, congestive heart failure, malignancy, CF
• v. in hospitalized patients (G- bacteria & staph important causes)
• post-op complications that impair clearance of respiratory secretions
• secondary infection following viral UTI

Question 14

Histologically, acute bronchopneumonia presents with

Answer 14

bronchioles and alveoli filled with neutrophils

Question 15

What are the complications of pneumonia?

Answer 15

• pleuritis
• pyothorax (pus in pleural space)
  
  • if becomes walled off by fibrous tissue = empyema
• abscesses
  
  • cavities contaning pus (purulent exudate)
  • commonly caused by staph aureus pneumonia, Klebsiella, or Pseudomonas
• chronic complications like bronchiectasis

Question 16

What causes lung abscess?

Answer 16

• typical complication of pneumonia caused by s. aureus, klebsiella, pseudomonas
• aspiration of infected material from URT or gastric contents
• distal to a bronchial obstruction by tumours
• septic emboli to the lung (eg in infective endocarditis)

Question 17

What are the causes of pneumonia with interstitial inflammation?

Answer 17

• viruses
• bacteria (atypical pneumonia)
• inflammatory responses to drugs
• immunological diseases
• collagen vascular diseases (lupus, vasculitis)
• radiation

Question 18

What is the pathology of infective pneumonia with interstitial inflammation caused by bacteria and viruses?

Answer 18

• widened alveolar septa
• infiltrated with lymphocytes, plasma cells, and macrophages
• bronchioloits

Question 19

What is the histologic presentation of interstitial pneumonia?

Answer 19

• may be oedema fluid, red cells, and fibrin in alvelolar spaces
• there are no alveolar neutrophils or inflammatory cells tf no consolidation
• macroscopically the lung appears wet, dark, and heavy

Question 20

What are the causes of atypical pneumonia?

Answer 20

• mycoplasma pneumoniae
• coxiella burnetti
• legionella spp
• chlamydia pneumoniae

Question 21

What is atypical pneumonia?

Answer 21

• community acquired pneumonia lacking clinical and radiological signs of consolidation

Question 22

What are the symptoms of atypical pneumonia?

Answer 22

• systemic symptoms predominate over respiratory
• malaise
• aches and pains
• headaches
• diarrhoea
• dry/non-productive cough or no cough at all
• often ambulatory despite extensive radiological signs of pneumonia
• clinical presentation follows intersitial pneumonia pathology eg no consolidation

Question 23

How does atypical pneumonia present on CXR?

Answer 23

• no consolidation pattern
• widespread changes throughout both lung fields
• reticulonodular infiltrate (dots and dashes)

Question 24

What is tuberculosis?

Answer 24

• chronic granulomatous pneumonia due to infection with Mycobacterium tuberculosis
• tubercle = granuloma

Question 25

What is primary TB?

Answer 25

* typically in childgood * pathology is characterised by a **Ghon's complex** * area of inflammation (peripheral mid-zone of lung) called a **Ghon focus** * mediastinal or hilar lymphnodes = granulomatous lymphadenopathy * **Ghon focus + enlarged lymph nodes = Ghon's complex** * granuloma consists of: * multinucleated giant cells * epitheliod macrophages * lymphocytes * central caseuous (cheesy) necrosis * usually asymptomatic * heals, often involving calcification * remains dormant until secondary infection arises

Question 26

Answer 26

tuberculous granuloma

Question 27

What are epitheliod macrophages?

Answer 27

* large, rounded pink cells * form aggregates

Question 28

What is the large arrow pointing to? The small arrow?

Answer 28

* large: caseous necrosis * small: multinucleated macrophages/giant cells

Question 29

What causes the formation of granulomas in TB?

Answer 29

* cell-mediated immune reaction type IV hypersensitivity * monocytes exit peripheral blood in the area of the infection * enter the tissue * stimulated by cytokines (IFNy) to become epitheloid macrophages * this forms a lump

Question 30

What is secondary TB?

Answer 30

* reactivation of dormant TB or reinfection * lobar pneumonia involving upper lobe * much more extensive caseation than primary due to stronger cell-mediated immune response * can erode bronchi causing cavitation

Question 31

What are the complications of secondary pulmonary TB?

Answer 31

* spread of caseation into surrounding lung * erosion of blood vessels --\> haemoptisis * erosion of the bronchial tree --\> cavitation and widespread infection to other parts of the lung via airways * pleural inflammation and fibrosis * lung scarring

Question 32

What are the clinical features of TB?

Answer 32

* variable weight loss * mailaise * fevers * night sweats * haemoptyisis * dyspnoea * chronic cough * **more severe and more acutely developed in pt with miliary and bronchopneumonia TB**

Question 33

How does TB spread within the body?

Answer 33

* via lymphatics * pleura * other parts of lung * other lung * via bronchial tree (infective caseous material in bronchial tree) * extensive TB bronchopneumonia * can be coughed up --\> laryngeal TB * then swallowed --\> intestinal and oesophageal TB * haematogenous spread * bia bloodstream to other organs * brain, urogenital tract, bones

Question 34

What is miliary TB?

Answer 34

* **most important form of extra-pulmonary TB** * occurs in primary and secondary TB * more common in secondary unles immuno-compromised * bacteria disseminates via bloodstream * can involve lung and/or multiple other organs: * liver, spleen, bone marrow, brain

Question 35

What is the pattern of miliary TB?

Answer 35

* numerous small granulomas (~2-3mm) in lung and other organs

Question 36

What is single-organ TB?

Answer 36

* usually caused by secondary TB with caseation * other organs can be seeded with TB from primary infection * seen in **spine (Potts disease)** and **urogenital tract** * in kidney, see butterfly-shaped lesions of caseous necrosis in upper pole * some cavitation occurs due to caseous material entering the collecting system