In 1935, Hamman and rich first described cases with rapidly progressing pulmonary fibrosis of unknown etiology. After that, the eponym, Hamman-Rich syndrome have been used to describe idiopathic pulmonary fibrosis. In 1975, Liebow came up with classification to distinguish between pulmonary fibrosis and idiopathic interstitial lung diseases. In 1986, Katzenstein used the term acute interstitial pneumonitis. Further studies helped to differentiate acute interstitial pneumonitis from pulmonary fibrosis.

The historical perspective of the acute interstitial pneumonitis is as follows:

• In 1935, the two pathologists Hamman and Rich have reported four cases of very rapidly progressing pulmonary fibrosis with identical histologic appearances.^[1]
• After this, the eponym, Hamman-Rich syndrome used to describe the cases of progressive pulmonary fibrosis of no identifiable etiology.
• After that Hamman-Rich syndrome used synonymously with idiopathic pulmonary fibrosis.
• In 1975, to avoid confusion between idiopathic pulmonary fibrosis and idiopathic interstitial lung diseases, Liebow proposed a classification.
  • Classification includes five distinct entities:
    • Usual interstitial pneumonia
    • Desquamative interstitial pneumonia
    • Bronchiolitis obliterans with interstitial pneumonia
    • Lymphoid interstitial pneumonia
    • Giant cell interstitial pneumonia.
  • He described more rapidly progressing pulmonary fibrotic diseases including Hamman-Rich syndrome under usual interstitial pneumonia.
• In 1986, eight cases of acute respiratory failure of unknown etiology, showing organizing diffuse alveolar damage on histopathological specimens were reported by Katzenstein.^[2]
  • They likened the disease to the acute interstitial fibrosis first reported by Hamman and Rich in 1935.
  • Then he proposed the term acute interstitial pneumonitis to differentiate from the acute respiratory distress syndrome, which has same pathology of organizing diffuse alveolar damage.
• Olson et al reviewed three of Hamman and Rich’s original cases. They confirmed the histopathologic lesion in those cases is diffuse alveolar damage. Those studies helped in establishing both acute interstitial pneumonitis and Hamman-Rich syndrome have same clinical and pathogical presentations and helped to distinguish pulmonary fibrosis from acute interstitial pneumonitis.
• In 2000, the American Thoracic Society and the European Respiratory Society international consensus published a statement stating acute interstitial pneumonitis is distinct from pulmonary fibrosis.^[3]