Pneumonias (Nagella) - 12/1/16

Question 1

What is pneumonia?

Answer 1

Infection of the lung parenchyma

Occurs when normal defenses are impaired (e.g. impaired cough reflex, damage to mucociliary escalator, or mucus plugging)

Question 2

Clinical features of pneumonia (5)

Answer 2

• Fever and chills
• Productive cough with yellow-green (pus) or rusty (bloody) sputum
• Tachypnea w/ pleuritic chest pain
  
  • Pt inspires → Stretches pleura → Bradykinin & PGE2 generated by inflammatory response
• Dullness to percussion (b/c of exudate)
• Elevated WBC count

Question 3

How is diagnosis made?

Answer 3

• CXR
• Sputum gram stain and culture
• Blood cultures

Question 4

What three patterns are classically seen on CXR?

Answer 4

1. Lobar pneumonia
   
   1. Consolidation that takes over entire lobe
2. Bronchopneumonia
   
   1. Consolidation that runs along small airways
3. Interstitial pneumonia
   
   1. No consolidation but inflammation within interstitium of lung (CT)

Question 5

Lobar pneumonia

Characterization

Bacterial or viral?

Classic gross phases

Answer 5

Characterization

• Consolidation of entire lobe of lung

Bacterial or viral

• Usually bacterial
  
  • Most common causes:
    
    • Steptococcus pneumoniae (95%)
      
      • Most common cause of community-acquired pneumonia and secondary pneumonia (bacterial pneumonia superimposed on a viral URT infection)
    • Klebsiella pneumoniae
      
      • ​Enteric flora that is aspirated
      • Affects malnourished and debilitated individuals, especially elderly, alcoholics, diabetics
      • Often accompanied by abscess

Classic gross phases

1. Congestion–due to congested vessels and edema
   
   1. Infection → congestion of vessels → dilation of vessels → inc. amt of blood in them → edema
2. Red hepatization–due to exudate, neutrophils, hemorrhage filling alevolar air spaces (gives normally spongy lung a solid consistency)
3. Gray hepatization–due to degradation of red cells within exudate
4. Resolution–healing
   
   1. Type II pneumocyte helps regenerate lining of alveolar air sacs

Question 6

Bronchopneumonia

Characterization

Bacterial or viral?

Answer 6

Characterization

• Scattered patchy consolidation centered around bronchioles
• Often multifocal and bilateral

Bacterial or viral:

• Caused by a variety of bacterial organisms
  
  • Staphylococcus aureus
    
    • ​2nd most common cause of secondary pneumonia
    • Often complicated by abscess or empyema
  • Haemophilus influenzae
    
    • ​Common cause of secondary pneumonia and pneumonia superimposed on COPD (leads to exacerbation of COPD)
  • Pseudomonas aeruginosa
    
    • Pneumonia in CF patients
  • Moraxella catarrhalis
    
    • ​Community acquired pneumonia and pneumonia superimposed on COPD (leads to exacerbation of COPD)
  • Legionella pneumophila
    
    • ​Community acquired pneumonia and pneumonia superimposed on COPD, or pneumonia in immunocompromised states
    • Transmitted from water source
    • Intracellular organism that is best visualized by silver stain

Question 7

Interstitial (Atypical) Pneumonia

Characterization

Bacterial or viral?

Answer 7

Characterization

• Diffuse interstitial infiltrates
• Presents with relatively mild upper respiratory symptoms (minimal sputum and low fever)
• ‘Atypical’ presentation

Bacterial or viral?

• Caused by bacterial or viruses
  
  • ​Bacteria
    
    • Mycoplasma pneumoniae
      
      • Most common cause of atypical pneumonia
      • Usually affects young adults (military, college dorms)
      • Complications: autoimmune hemolytic anemia (IgM against I antigen on RBCs cause cold hemolytic anemia) and erythema multiforme
      • Not visible on garm stain due to lack of cell wall
    • Chlamydia pneumoniae
      
      • Second most common cause of atypical pneumonia in young adults
    • Coxiella burnetii
      
      • Atypical pneumonia with high fever (Q fever)
      • Seen in farmers/veterinarians (Coxiella spores deposited on cattle by ticks or are present in cattle placenta)
      • RIckettsial organism, but distinct from most rickettsiae b/c it:
        
        • 1. Causes pneumonia
        • 2. Does not require arthropod vector for transmission (survives as highly heat-resistant endospores)
        • 3. Does not produce skin rash (whereas most ricketsial organisms do)
  • ​​​Virus
    
    • Influenza virus
      
      • Atypical pneumonia in elderly, immunocompromised, and pre-existing lung disease pts
      • ALso inc. risk for superimposed S. aureus or H. influenza bacterial pneumonia
    • Cytomegalovirus (CMV)
      
      • Atypical pneumonia with post-transplant immunosuppressive therapy
    • Respiratory syncytial virus (RSV)
      
      • Most common cause of atypical pneumonia in infants