Page 385 - Concise Pathology for Exam Preparation ( PDFDrive )

370 SECTION II Diseases of Organ Systems

Pathogenesis (Flowchart 13.6)

Epithelial activation/epithelial injury

Senescence and apoptosis Inflammation and induction of T 2 Type T cell response
H

Telomere shortening Accumulation of leukocytes and
immune effector cells in the alveoli

Reduced telomerase Distortion of normal architecture of alveolar walls
Release of TGF- 1 from
Mutation in injured Type I pneumocytes,
telomerase which inhibits caveolin-1
(endogenous inhibitor of
pulmonary fibrosis)
Familial cases Induction of exuberant fibroblastic/
myofibroblastic response

End-stage fibrotic lung (honeycomb fibrosis)
(alveoli are replaced by cystic spaces lined by
Type II pneumocytes and thick bands of collagen)
FLOWCHART 13.6. Pathogenesis of ILD.

Q. Write briefly on idiopathic pulmonary fibrosis (IPF).

Ans. IPF is characterized by the following salient features:
• Causes progressive interstitial fibrosis leading to lung failure
• Usually affects individuals older than 50 years
• Histological picture labelled as UIP but can have overlapping features with other entities
(connective tissue disorders, hypersensitivity pneumonia and asbestosis). Diagnosis
should be based on the complete clinics-radiologic picture and morphology.

Pathogenesis
Both genetic and environmental factors implicated.
1. Environmental factors: Smoking, exposure to toxins such as metal fumes, occupa-
tional exposure (farming, stone polishing and hair dressing) damages alveolar epithe-
lium activates immune responses to generate profibrogenic factors resulting in collagen
production and fibrosis.
2. Genetic factors: Telomerase mutations, surfactant mutations and genetic abnormality
leading to increased secretion of MUC5B, an abnormal mucin that predisposes to
alveolar epithelial injury.

Histopathology
• Prominent fibrosis along the interlobular septae and subpleural region with patchy
interstitial fibrosis.
• Early lesions are cellular, contain plump fibroblasts and late lesions are densely collagenized.
• Fibrosis induces distortion of cellular architecture and formation of cystic spaces resulting
in a ‘honeycoomb appearance’.
• Chronic inflammation may be seen in the areas of fibrosis.

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