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RS Pathology

Respiratory System Pathology - Hypersensitivity Pneumonitis & Fibrosing Diseases

What is hypersensitivity pneumonitis? an immunologically mediated inflammatory lung disease that primarily affects the alveoli and is often called allergic alveolitis
The damage occurs at the level of: Alveolar sacs
What are the syndromes and their adjacent antigens? Farmer's lung -Moldy hay--Micropolyspora Maple bark disease-Moldy maple bark -Cryptostroma Pigeon breeder's lung-Pigeon droppings-Pigeon serum proteins
How is hypersensitivity pneumonitis immunologically mediated? Increased T lymphocytes of CD4+ / CD8+ Specific Abs in serum Complement and Igs demonstrated within vessels by immunofluorescence- type III Noncaseating granulomas in two thirds of patients - role for type IV
Morphology of hypersensitivity pneumonitis: Patchy mononuclear cell infiltrates in the pulmonary interstitium- mainly lymphocytes Interstitial non-caseating granulomas are present in about 2 thirds In advanced cases, diffuse interstitial fibrosis
Clinical manifestations of hypersensitivity pneumonitis: 1) Acute reaction 2) Chronic disease
What symptoms appear in the case of an acute reaction? Fever Cough Dyspnea 4 to 8 hours after exposure
In case of chronic disease, what symptoms appear? Insidious onset of cough Dyspnea Malaise Weight loss Failure to remove the inciting agent eventually results in an irreversible chronic interstitial pulmonary disease
Idiopathic pulmonary fibrosis (IPF) is also known as: cryptogenic fibrosing alveolitis
IPF is characterized by: Patchy but progressive bilateral interstitial fibrosis
In advanced cases, IPF is caused by: Severe hypoxemia Cyanosis
Epidemiology of IPF: Males are affected more often than females Two thirds of patients are older than 60 years of age at presentation
The radiologic and histologic pattern of fibrosis is referred to as: Usual interstitial pneumonia (UIP)
Pathogenesis of IPF: Repeated cycles of epithelial activation/injury by unidentified agent Histopathologic features include inflammation and induction of TH2 type T cell response with eosinophils, mast cells, IL-4, and IL-13 in the lesions
Abnormal epithelial repair at the sites of damage and inflammation gives rise to exuberant fibroblastic or myofibroblastic proliferation leading to characteristic fibroblastic foci
Actions of TGF-B1 in IPF: Induces transformation of fibroblasts into myofibroblasts leading to excessive and continuing deposition of collagen and ECM . Downregulates fibroblast caveolin-1, which acts as an endogenous inhibitor of pulmonary fibrosis
Morphology in UIP; Over time these areas become more collagenous and less cellular Existence of both early and late lesions (temporal heterogeneity)
The dense fibrosis causes collapse of alveolar walls Formation of cystic spaces lined by hyperplastic type II pneumocytes or bronchiolar epithelium (honeycomb fibrosis)
What secondary hypertensive pulmonary changes are also seen in IPF? Intimal fibrosis Medial thickening of pulmonary arteries
What are the clinical features of IPF? IPF usually manifests insidiously, with gradual onset of a nonproductive cough and progressive dyspnea Dry crackles during inspiration. Cyanosis, cor pulmonale, and peripheral edema may develop in later stages of the disease
How is IPF diagnosed? The clinical and radiologic findings are diagnostic Surgical lung biopsy
Treatment of IPF: Progression of IPF is relentless despite medical therapy, and the mean survival is 3 years or less Lung transplantation is the only definitive therapy available
What is pneumoconioses? Non-neoplastic lung reaction to inhalation of mineral dusts, organic, and inorganic materials
Mineral dust pneumoconioses results most commonly from: Coal dust Silica Asbestos
If a particle of 5-10 microns enters the lung, what happens? Particles are unlikely to reach distal airways
If a particle is smaller than 0.5 microns enters the lung, what happens? Particles move into and out of alveoli, often without substantial deposition and injury
If a particle of 1-5 microns enters the lung, what happens? These particles are the most dangerous, because they get lodged at bifurcation of the distal airways
What is the reactivity of coal dust in the lungs? Coal dust is relatively inert, and large amounts must be deposited before lung disease is clinically detectable
What is the reactivity of Silica, asbestos, and beryllium in the lungs? More reactive than coal dust, resulting in fibrotic reactions at lower concentrations
What is the key cellular element in the initiation and perpetuation of lung injury and fibrosis? Alveolar macrophages
How do alveolar macrophages initiate and perpetuate fibrosis? Particles activate inflammasome and induce IL-1 Reactive particles trigger macrophages Release inflammatory mediators Initiate fibroblast proliferation/ collagen deposition Reach lymphatics directly or by migrating macrophages- initiate immune resp.
How does tobacco smoke affect inhaled particles? Tobacco smoking worsens the effects of all inhaled mineral dusts, more with asbestos than other particles
Different categories of coal workers' pneumonoconioses: 1) Pulmonary anthracosis 2) Simple coal worker's pneumoconiosis (CWP) 3) Complicated CWP or (PMF)
What is pulmonary pneumoconioses? The most benign coal-induced pulmonary lesion in coal miners
Pulmonary pneumoconioses is seen in: 1) Coal miners 2) Urban dwellers 3) Tobacco smokers
What occurs in pulmonary pneumoconioses? Inhaled carbon pigment is engulfed by alveolar or interstitial macrophages, which then accumulate in the connective tissue along the lymphatics, including the pleural lymphatics, or in lymph nodes The pigment accumulates without cellular reaction
What occurs in simple coal workers' pneumoconioses? Accumulations of macrophages occur with little to no pulmonary dysfunction
Coal macules consist of: Dust-laden macrophages
Coal Nodules consist of: Dust-laden macrophages Small amounts of collagen fibers arrayed in a delicate network
Which zones of the lung in CWP are mostly affected? The upper lobes and upper zones of the lower lobes
What occurs in Complicated CWP or (PMF)? Fibrosis is extensive and lung function is compromised and Occurs on a background of simple CWP by coalescence of coal nodules and generally requires many years to develop
Morphology of Complicated CWP or PMF? Multiple, blackened scars larger than 2 cm, sometimes up to 10 cm in diameter On microscopic examination- lesions are seen to consist of dense collagen and pigment Less than 10% of cases of simple CWP progress to PMF
Progressive massive fibrosis (PMF) applies to: Confluent fibrosing reaction in the lung
Clinical features of Complicated CWP: Benign disease Little decrement in lung function Increasing pulmonary dysfunction, pulmonary hypertension, and cor pulmonale
Progression from CWP to PMF has been linked to A variety of conditions including coal dust exposure level and total dust burden Unfortunately, PMF has a tendency to progress even in the absence of further exposure
Once smoking-related risk has been taken into account No increased frequency of lung carcinoma in coal miners Distinguishes CWP from both silica and asbestos exposures
Created by: Ulaisl



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