Acute Interstitial Pneumonia

(aka Hamman-Rich syndrome)

Epidemiology

  • Mean Age of Onset: 50’s (Range: 7-83 y/o)
  • Rare fulminant form of acute onset lung injury (ALI)
  • Usually occurs in a previously healthy individual
  • Probably represents what Hamman and Rich described as Acute Diffuse Interstitial Fibrosis (Hamman-Rich Syndrome)
  • Relationship to Smoking: unknown
  • Sex: no sex predilection
  • Prodrome: prodromal illness lasting 7-14 days is common

Etiology

  • Unknown

Physiology

  • [[Diffuse Alveolar Damage]] -> [[Acute Lung Injury-ARDS]], and/or [[Diffuse Alveolar Hemorrhage]]
    • Exudation of serum proteins and RBC into alveolar spaces
    • Necrotic, sloughed alveolar epithelium
    • Edematous interstitium
    • Hyaline membranes (eosinophilic debris consisting of necrotic epithelial cells, protein, and fibrin) form within alveoli
  • Reparative/Organizing Phase:
  • Irreversible Fibrosis/Honeycombing: may occur with protracted or repeated injury

Pathology

  • Diffuse Alveolar Damage
  • Pathologic Features:
    • Temporal Appearance: uniform
    • Interstitial Inflammation: scant
    • Collagen Fibrosis: none
    • Fibroblast Proliferation: diffuse
    • Microscopic Honeycombing: none
    • Intra-Alveolar Macrophage Accumulation: none
    • Hyaline Membranes: occasional, focal

Diagnosis

  • FOB:
  • ABG: hypoxemia
  • OLB: usually required for diagnosis
  • CXR/Chest CT Patterns:
    • Diffuse Bilateral Airspace Opacification (similar to ARDS): may be predominantly subpleural in location
      • Bilateral, Patchy, Symmetric Ground-Glass:
      • Bilateral Airspace Consolidation: may be seen
      • Mild Honeycombing (Usually <10%): may occur
  • CBC: not helpful in diagnosis

Clinical

  • Interstitial Pulmonary Fibrosis (see [[ILD-Etiology]])
    • Acute onset: symptoms may progress over days-weeks
    • Dyspnea:
    • Fever:
    • Cough:
  • Acute Lung-ARDS (see [[Diffuse Alveolar Damage]], [[Acute Lung Injury-ARDS]], and [[Diffuse Alveolar Hemorrhage]]

Treatment

  • Poor response to steroids (62% mortality rate)

Prognosis

  • Mortality Rate: 62%
  • Most patients die within 3 months of presentation
  • Complete recovery is possible though (unlike UIP)
  • In those that recover, substantial recovery of lung function occurs
  • Some survivors manifest recurrences and chronic, progressive ILD

References

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