SPECIAL SELECTED TOPICS- RESPIRATORY SYSTEM DISORDERS-SSTRSDO-QAA 013

1. Describe the main pathologic characteristics of diffuse interstitial lung disease and classify it according to etiology.

Diffuse interstitial lung diseases are characterized by chronic inflammation and fibrosis involving the pulmonary interstitium and alveolar walls. They reduce lung compliance and impair gas exchange. Histologically, there is varying degrees of interstitial inflammation, fibroblast proliferation, and collagen deposition.

Advanced disease results in honeycomb lung due to cystic fibrotic spaces. Etiologically, they are classified into idiopathic interstitial pneumonias, occupational lung diseases, drug-induced lung disease, connective tissue disease-associated disorders, hypersensitivity pneumonitis, and granulomatous diseases such as sarcoidosis.

Idiopathic pulmonary fibrosis is the most common type. Progressive fibrosis causes restrictive lung disease.

Pulmonary hypertension may develop in advanced cases. Respiratory failure is the major cause of death.

2. What are the morphologic manifestations of diffuse interstitial disease of the lung?

The lungs become firm, stiff, and reduced in compliance because of widespread fibrosis. Gross examination shows diffuse scarring, particularly in the lower lobes in many forms of disease. Microscopically, the alveolar septa are thickened by chronic inflammatory cells and collagen deposition.

Fibroblast proliferation contributes to progressive fibrosis. Type II pneumocyte hyperplasia is often present during repair. Advanced disease produces honeycomb lung with multiple cystic airspaces lined by bronchiolar epithelium.

Pulmonary vessels may show medial hypertrophy due to pulmonary hypertension. Gas exchange is impaired because of increased diffusion distance.

Progressive fibrosis eventually causes respiratory insufficiency. The severity depends on the extent and duration of interstitial damage.

---

DR.C.GANESAN M.D

PROFESSOR OF MEDICINE