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Other interstitial pneumonitis / fibrosis

Usual interstitial pneumonitis (UIP) / Idiopathic pulmonary fibrosis

Reviewers: Elliot Weisenberg, M.D. (see Reviewers page)
Revised: 25 September 2011, last major update September 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.

Clinical features

● Also called chronic interstitial pneumonitis, cryptogenic fibrosing alveolitis (in Europe)
● Clinicopathologic syndrome is known as idiopathic pulmonary fibrosis
● Pathologic pattern occurs in a variety of clinical settings
● Patients usually 40-70 years old at presentation
● 50% have unknown cause with insidious onset (exertional dyspnea with non-productive cough) and chronic evolution
● Complications include secondary pulmonary hypertension, cor pulmonale, cardiac failure
● Some cases may represent a form of immune-complex lung disease associated with collagen vascular diseases or autoimmune diseases (Sjogren’s, ulcerative colitis, rheumatoid disease, scleroderma, Raynaud’s disease and thyroid disease)
● Most cases have circulating immune complexes; 30% have serum antinuclear antibodies (ANA)
● May be associated with neurofibromatosis, pulmonary veno-occlusive disease or adenocarcinoma if atypical foci of acinar and squamous proliferation are present
● May represent a common pathway following repeated alveolar wall injury from various causes with inflammation and fibroblastic/myofibroblastic proliferation
● An aberrant Wnt/B-catenin signaling pathway may be related to abnormal remodeling
● Increased TGF-B1 activity likely has role in abnormal fibrosis
● Reduced diffusing capacity is mainly due to ventilation-perfusion mismatch from ventilation of lung tissue with capillary destruction and perfusion of underventilated alveoli; smaller component due to reduced diffusion across a fibrotic alveolar septa
Diagnosis: in the appropriate clinical setting, high resolution CT scanning is diagnostic and biopsy is seldom performed


● Steroids (20% improve); eosinophilia is associated with a poor response, more functional abnormalities and worse prognosis
● Mean survival 3-5 years, mortality 66%

Gross description

● Shrunken lung with "hobnailed" pleura due to retraction by underlying fibrous scarring

Gross images

Honeycomb pattern

Micro description

● Characteristic temporal and regional heterogeneity of morphologic changes
Major features: established fibrosis, patchy parenchymal involvement with subpleural/paraseptal predominance, fibroblastic foci, typically mild interstitial chronic inflammation and honeycomb change when advanced
Minor (or secondary) changes: alveolar macrophage accumulation, follicular hyperplasia, smooth muscle hypertrophy/hyperplasia, endartertitis, alveolar neutrophil accumulation, bronchiolar, bony, fatty and squamous metaplasia, mild pleuritis and pleural fibrosis, cholesterol clefts, subpleural blebs, prominent eosinophil accumulation and focal alveolar fibrin
Pertinent negative features: lack of inorganic dusts, lack of granulomas and lack of Langerhans’ cells

EM description

● Fibrosis due to migration of activated mesenchymal cells through defects in epithelial lining and its basement membrane from interstitial to intraluminal compartment
● Replacement of alveolar type I cells by hyperplastic alveolar type II cells

Differential diagnosis

● Pneumoconiosis
● Hypersensitivity pneumonitis
● Bronchiolitis obliterans organizing pneumonia
● Oxygen toxicity pneumonitis
● Scleroderma
● Radiation injury
● Non-specific interstitial pneumonia (NSIP)

Additional References

Am J Surg Pathol 2002;26:1567, Am J Respir Crit Care Med 2000;161:646

End of Lung-nontumor > Other interstitial pneumonitis / fibrosis > Usual interstitial pneumonitis (UIP) / Idiopathic pulmonary fibrosis

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