Types

• Lobar
  • may involve entire lobe or lung
• Bronchopneumonia
  • patchy distribution involving ≥ 1 lobe involving bronchioles and alveoli
• Interstitial / Atypical pneumonia
  • diffuse distribution involving ≥ 1 lobe involving interstitial areas
• Cryptogenic Organizing Pneumonia (COP) previously called B O O P
  • noninfectious with unknown etiology / idiopathic 
  • ⊝ sputum and blood cultures, no response to antibiotics

 

Characteristics

Lobar

Intra-alveolar exudates cause consolidation

Bronchopneumonia

Acute inflammatory infiltrates from bronchioles into adjacent alveoli

Interstitial

• Diffuse patchy inflammation localized to interstitial areas at alveolar walls
• Indolent course

COP

• Variable dense chronic inflammation
• NO honeycomb change/fibrosis
• Alveolar architecture is usually preserved
• Loose aggregates of fibroblasts in ground substance (Masson bodies)

Microbial Associations

Lobar – S L K

• Strep. pneumonia
  • MCC community-acquired lobar pneumonia
  • middle- aged adults
• Legionella
  •  i/compromised
  • intracellular
  • transmitted via water source
• Klebsiella
  • malnourished debilitated individuals
  • elderly in nursing homes, alcoholics, and diabetics (enteric flora that is aspirated due to gastroparesis)
  • thick mucoid capsule results in gelatinous sputum (currant jelly)
  • often complicated by abscess

Bronchpneumonia

• S pneumoniae, Klebsiella
• H.influenza
• Staph. aureus
  • commonly a secondary superimposed pneumonia (bacterial / viral infection)
  • often complicated by abscess or empyema

Interstitial

• Mycoplasma pneumoniae
  • MCC in young adults
  • classically, military recruits or college students living in a dormitory
  • complications include cold autoimmune hemolytic anemia (IgM against antigens on RBCs) and erythema multiforme
  • not visible on gram stain due to lack of cell wall

• Chlamydophila pneumoniae / Chlamydia psittaci
  • 2nd MCC in young adults
• Respiratory syncytial virus (RSV)
  • MCC in infants
• Cytomegalovirus (CMV)
  • post-transplant + immunosuppressive therapy
• Influenza
  • in the elderly, immunocompromised, and those with preexisting lung disease
  • increases the risk for superimposed S. aureus or H. influenzae bacterial pneumonia

• Coxiella
  • atypical pneumonia with high fever (Q fever)
  • seen in farmers and veterinarians
  • spores deposited on cattle by ticks or are present in cattle placentas
    • a rickettsial organism, but distinct from most rickettsiae because it :
      (1) causes pneumonia
      (2) does not require arthropod vector for transmission [survives as highly heat-resistant endospores), and
      (3) does not produce a skin rash.

Diseases

• COPD
  • Moraxella,
  • H.influenza
  • Legionella (silver staining)
• CF
  • Pseudomonas. aeruginosa