Respiratory System Pathology - Hypersensitivity Pneumonitis & Fibrosing Diseases
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| What is hypersensitivity pneumonitis? | an immunologically mediated inflammatory lung
disease that primarily affects the alveoli and is often
called allergic alveolitis
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| The damage occurs at the level of: | Alveolar sacs
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| 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
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| 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
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| 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
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| Clinical manifestations of hypersensitivity pneumonitis: | 1) Acute reaction
2) Chronic disease
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| What symptoms appear in the case of an acute reaction? | Fever
Cough
Dyspnea
4 to 8 hours after exposure
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| 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
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| Idiopathic pulmonary fibrosis (IPF) is also known as: | cryptogenic fibrosing alveolitis
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| IPF is characterized by: | Patchy but progressive bilateral interstitial fibrosis
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| In advanced cases, IPF is caused by: | Severe hypoxemia
Cyanosis
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| Epidemiology of IPF: | Males are affected more often than females
Two thirds of patients are older than 60 years of age at presentation
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| The radiologic and histologic pattern of fibrosis is referred to as: | Usual interstitial pneumonia (UIP)
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| 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
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| Abnormal epithelial repair at the sites of damage and inflammation gives rise to exuberant fibroblastic or myofibroblastic proliferation leading to | characteristic fibroblastic foci
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| 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
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| Morphology in UIP; | Over time these areas become more collagenous and less cellular
Existence of both early and late lesions (temporal heterogeneity)
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| The dense fibrosis causes | collapse of alveolar walls
Formation of cystic spaces lined by hyperplastic type II pneumocytes or bronchiolar epithelium (honeycomb fibrosis)
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| What secondary hypertensive pulmonary changes are also seen in IPF? | Intimal fibrosis
Medial thickening of pulmonary arteries
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| 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
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| How is IPF diagnosed? | The clinical and radiologic findings are diagnostic
Surgical lung biopsy
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| 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
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| What is pneumoconioses? | Non-neoplastic lung reaction to inhalation of mineral dusts, organic, and inorganic materials
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| Mineral dust pneumoconioses results most commonly from: | Coal dust
Silica
Asbestos
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| If a particle of 5-10 microns enters the lung, what happens? | Particles are unlikely to reach distal airways
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| 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
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| 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
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| 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
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| What is the reactivity of Silica, asbestos, and beryllium in the lungs? | More reactive than coal dust, resulting in fibrotic reactions at lower concentrations
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| What is the key cellular element in the initiation and perpetuation of lung injury and fibrosis? | Alveolar macrophages
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| 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.
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| How does tobacco smoke affect inhaled particles? | Tobacco smoking worsens the effects of all inhaled mineral dusts, more with asbestos than other particles
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| Different categories of coal workers' pneumonoconioses: | 1) Pulmonary anthracosis
2) Simple coal worker's pneumoconiosis (CWP)
3) Complicated CWP or (PMF)
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| What is pulmonary pneumoconioses? | The most benign coal-induced pulmonary lesion in coal miners
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| Pulmonary pneumoconioses is seen in: | 1) Coal miners
2) Urban dwellers
3) Tobacco smokers
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| 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
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| What occurs in simple coal workers' pneumoconioses? | Accumulations of macrophages occur with little to no pulmonary dysfunction
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| Coal macules consist of: | Dust-laden macrophages
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| Coal Nodules consist of: | Dust-laden macrophages
Small amounts of collagen fibers arrayed in a delicate network
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| Which zones of the lung in CWP are mostly affected? | The upper lobes and upper zones of the lower lobes
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| 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
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| 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
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| Progressive massive fibrosis (PMF) applies to: | Confluent fibrosing reaction in the lung
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| Clinical features of Complicated CWP: | Benign disease
Little decrement in lung function
Increasing pulmonary dysfunction, pulmonary hypertension, and cor pulmonale
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| 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
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| 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
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