Infections of the lung

Question 1

Pneumonitis vs pneumonia

Answer 1

• Pneumonitis: inflammation and consolidation of the lung parenchyma, but not necessarily caused by infection (hypersensitivity)
• Pneumonia (PNA): inflammation and exudative solidification of the lung (consolidation) due to an infectious agent
• Possible types of PNA: community acquired acute/atypical, hospital acquired, aspiration, chronic PNA, necrotizing PNA and lung abscesses

Question 2

Community acquired acute PNA (CAAcP)

Answer 2

• Usually due to bacteria: strep pneumo (most common), H influenza, Moraxella Catarrhalis, S aureus, P aeruginosa, L pneumophila (legionella)
• Can be either bronchopneumonia or lobar pneumonia pattern
• Bronchopneumonia: diffuse foci of consolidation affecting multiple lobes
• Lobar: globally/uniformly affects a single lung
• Sx: fever, chills, cough, dyspnea, chest pain, coryza

Question 3

Pathogenesis of CAAcP

Answer 3

• 4 stages of CAAcP
• First there is congestion of the vasculature
• Then there is red hepatization, in which there is exudation of inflammatory cells (mostly PNMs into alveolar lumens), along w/ congested capillaries
• Inflammation will eventually leave behind necrotic inflammatory debris in the alveoli
• The lung becomes gray and fibrosed (gray hepatization)
• Micoscopically during gray hepitization there are fibrous plugs resulting in organizing of the necrotic exudate
• If the organization occurs quickly there can be resolution (final stage) and return to normal lung

Question 4

Community acquired atypical PNA (CAAtP)

Answer 4

• An infectious interstitial PNA that most commonly affects children and young adults
• Most common etiology is Mycoplasma pneumonia (also viruses and chlamydia pneumonia can)
• Organisms attach to the upper respiratory tract and extend distally
• Once in alveoli there is inflammation, which is predominantly interstitial w/ widened septa and scattered PMNs (patchy or lobar)
• Atypical b/c of lack of classic PNA presentation (less sputum, no cough, may think they have a cold)

Question 5

Hospital acquired PNA (HAP)

Answer 5

• Usually in pts who are under ventilators, have IV caths, severe underlying disease, immunosuppression or prolonged antibio Rx
• Organisms: E Coli, P Aeruginosa, S aureus

Question 6

Aspiration PNA

Answer 6

• Debilitated pts and unconscious individuals at risk for aspirating gastric or oral contents
• Possibly produces granulomatous alveolar exudate
• But more often produces abscesses: aspiration PNA is most common cause of lung abscesses

Question 7

Chronic PNA

Answer 7

• Usually a localized process that usually causes chronic granulomatous inflammation
• Most commonly TB, but can also be fungal (histoplasma, blastomycoses, coccidiomycoses)

Question 8

Mycobacterium tuberculosis complex

Answer 8

• Unpasteurized milk: M bovis
• Initial 1o Sx characteristically ASx, but indefinitely at risk for reactivation
• Risk factors: blacks, native american, diabetes, etoh, malnutrition, heart disease, chronic lung disease, ARDS
• Pathogenesis: host response is type IV delayed hypersensitivity, causes caseous necrosis granulomatous reaction
• Acid-fast bacillus are resistant to intracellular digestion
• ASx disease resides in lower lungs, upon activation and Sx showing the disease is seen in upper (apices) lungs
• Caseous necrosis: Ghon focus
• Can spread hematogenously to anywhere, especially to meninges in children

Question 9

TB vs sarcoidosis

Answer 9

• TB has necrotizing granulomas, sarcoid has non-necrotizing

- Sarcoid tends to cluster around lymphatics and airways