Respiratory Pathology of ILD Flashcards
What is the pulmonary interstitium composed of?
- alveolar lining cells (types 1 and 2)
- thin elastin-rich connective component, containing capillary blood vessels
the interstitium is normally small and thin. True/ False?
True
It is very thin so that efficient gas exchange can occur.
Interstitial Lung diseases are characterised by 2 stages: early stage and late stage. Describe these stages.
Early stage: alveolitis (injury with inflammatory cell infiltration). Acute ILD is exemplified by ARDS
Late stage is characterised by fibrosis
What causes the clinical effects of ILDs?
hypoxia (respiratory failure) and cardiac failure
Name some causes of ILD
- environmental (minerals, drugs, radiation)
- idiopathic (connective tissue diseases, fibrosing alveolitis AKA IPF)
transbronchial biopsy
special forceps used at bronchoscopy (biopsy helps diagnose ILD)
thoracoscopic biopsy
more invasive than transbronchial biopsy, but more reliable and generates far more tissue
Name some chronic ILDs.
- fibrosing alveolitis (IPF)
- sarcoidosis
- pneumoconiosis
- extrinsic allergic alveolitis
- connective tissue diseases
fibrosing alveolitis AKA Idiopathic Pulmonary Fibrosis
AKA usual interstitial pneumonia (UIP)
This is a progressive interstitial fibrosis of unknown cause. Associated inflammation (variable). Finger clubbing. There is subpleural and basal fibrosis. Terminally, the lung structure is replaced by dilated spaces surrounded by fibrous walls. These walls are very thick (difficult gas exchange).
In late stages, IPF is characterised by “honeycombing” histology (thick fibrosed walls).
SCARRING IS BASAL. There will be dense fibrous tissue (not very elastic) around the edges - this acts as a splint, which decreases lung volume
Extrinsic Allergic Alveolitis (hypersensitivity pneumonitis)
This is a chronic INFLAMMATORY disease of the small airways, interstitium, with occasional granulomas. (There is a bit of fibrosis).
Allergic origin: type 3 and type 4 hypersensitivity reaction
Causes of EAA
-thermophilic bacteria (Farmer’s lung)
-Avian proteins (Bird fancier’s lung)
-fungi (malt worker’s lung)
Preciptins (antibodies) are usually detectable in serum, but unusual cases are biopsied.
Sarcoidosis
A multisystem granulomatous disorder of unknown cause (defined histologically). Pulmonary involvement is common (other symptoms are uveitis, erythema nodosum, lymphadenopathy, hypercalcaemia). Most cases are mild and self-limiting. There may be enlarger hilar lymph nodes on CXR. Transbronchial biopsy will show granulomas, but NOT MUCH INFLAMMATION Must also use a stain and look for organisms e.g. TB (TB can also cause erythema nodosum, but in TB the people are usually much sicker). There is a “honeycomb” lung in sarcoidosis, with APICAL SCARRING. Scarring is due to long-standing sarcoid. Calcifications may form after long-term.
Pulmonary involvement in connective tissue diseases?
-interstitial fibrosis (milder than fibrosing alveolitis)
-pleural effusions
-rheumatoid nodules (these look like TB, but no organisms are identified - so it is a nodule)
Connective tissue disease affect all body systems and are mostly autoimmune.
Pneumoconiosis
This is lung disease caused by mineral dust exposure e.g:
- asbestosis
- coal worker’s lung
- silicosis
Why do some people get pneumoconiosis and others who are exposed to the same dusts are fine?
Disease depends on:
- particle size (small get trapped in the lung, smaller go in and out and cause little damage)
- reactivity of particle (asbestos is very reactive, carbon pigment isn’t)
- clearance of particle (e.g. by coughing)
- host response
