Respiratory: Pathology of Interstitial Lung Disease Flashcards
What is the interstitial part of lungs?
Where gas exchange occurs and includes the alveolar lining cells:
Type 1
Type 2
Lung facilitation of gas exchange?
Thin elastin-rich connective component containing capillary blood vessels
Stages of interstitial lung disease?
Early stage - alveolitis (inflammation of alveoli with inflammatory cell infiltration)
Late stage - characterised by FIBROSIS
Why do clinical effects of ILD arise?
Hypoxia (respiratory failure) - not maintaining normal arterial PO2
Cardiac failure - long-standing hypoxia leads to pulmonary hypertension and thus to cardiac failure
Example of acute ILD?
Adult Respiratory Distress Syndrome (ARDS) - widespread inflammation in the lungs, triggered by trauma, pneuomonia, sepsis, etc
Causes of ILD?
Environmental - minerals, drugs, radiation (with radiotherapy can develop long-standing radiation pneumonitis characterised by ILD and scarring), post-ARDS and also due to hypersensitivity on exposure, to for example mouldy hay, avian proteins
Unknown (idiopathic) - e.g: connective tissue diseases and fibrosing alveolitis
Diagnosis of ILD?
Based on clinical features often with BIOPSY:
Transbronchial biopsy - special forceps used at bronchoscopy (good for sarcoidosis)
Thoracoscopic biopsy - more invasive but more reliable and generates more tissue
Types of CHRONIC ILD?
Fibrosing alveolitis Sarcoidosis Extrinsic allergic alveolitis (HYPERSENSITIVITY PNEUMONITIS) Pnuemoconiosis Connective tissue disease
What is fibrosing alveolitis?
AKA IDIOPATHIC PULMONARY FIBROSIS, Cryptogenic Fibrosing Alveolitis (CFA) and Usual Interstitial Pneumonia (UIP)
Progressive interstitial fibrosis of unknown cause with variable associated inflammation
Signs - finger clubbing, scarring on CXR, RESTRICTIVE pattern with pulmonary function tests and breathlessness
Pathology of fibrosing alveolitis?
Subpleural and basal fibrosis
Variable inflammatory component
Terminally, lung structure replaced by dilated spaces surrounded by fibrous walls (HONEYCOMBING)
Scar tissue fails to stretch like lung tissue and becomes splinted (vital capacity decreases as lung cannot expand)
What is extrinsic allergic alveolitis?
AKA hypersensitivity pneumonitis
Chronic INFLAMMATORY disease characterised by small airways, inflammatory interstitial expansion (tissue between the pulmonary alveoli and the bloodstream) and occasional granulomas
Allergic origin of extrinsic allergic alveolitis?
Types III hypersensitivity (immune complexes deposited in lung cause inflammation)
Type IV hypersensitivity
Causes of extrinsic allergic alveolitis?
Many are occupational:
Thermophilic bacteria - in Farmer’s Lung
Avian proteins - Bird Fancier’s Lung
Fungi - Malt Worker’s Lung
Diagnosis of extrinsic allergic alveolitis?
Precipitins (antibodies) often detectable in serum
Unusual cases come to biopsy
What is sarcoidosis?
Multi-system GRANULOMATOUS disorder (not of infective origin) of unknown causes with common pulmonary involvement (granulomatous inflammation in lungs - Type IV hypersensitivity)
