Restrictive (interstitial) lung diseases Flashcards
Where is the interstitium of the lung?
Connective tissue space around the airways and vessels. Space between BM and alveolar walls. Normally, type 1 pneumocytes and capillary endothelial BM are in direct contact. In interstitial lung disease, they are pushed apart.
How big should the interstitial space be?
As small as possible to facilitate the exchange of CO2 and O2.
What happens in restrictive/interstitial lung disease?
In restrictive (diffuse) interstitial lung disease:
- Reduced lung compliance leads to stiff lungs/non-stretchy
- Low FEV1 and low FVC but FEV1/FVC normal ratio as there is no airflow limitation
- Reduced gas transfer (Tco or Kco): this shows how fast CO gas is transferred in the blood and there will be a diffusion abnormality
- Ventilation/perfusion imbalance: when small airways are affected by pathology
Normal FEV1/FVC in restrictive lung disease: 0.85; FEV1 is 1.8L and FVC is 2.1L
(Compared to normal ratio which is 0.81; FEV1 4L and FVC 4.9L)
What is the presentation of diffuse lung disease?
Lungs small on CXR, dyspnoea rest/exertion, type 1 respiratory failure (PaO2).
What is the cause of diffuse interstitial lung disease?
Parenchymal (interstitial) tissue injury. There is an acute or chronic response to this. Chronic responses: usual interstitial pneumonitis (UIP), granulomatous responses or others –> all can lead to fibrosis or end-stage honeycomb lung (irreversible).
Describe an acute response to interstitial tissue injury.
DAD (diffuse alveolar damage)/ARDS. Associated with: major trauma, chemical injury/toxin inhalation, circulatory shock, drugs, infection, autoimmune responses, radiation or can be idiopathic.
What is the process of DADS?
Day 1: oedema - massive outpouring of fluid due to damage. Proteins precipitate within the alveolar airspace which leads to the development of hyaline membranes around day 3-5 –> EXUDATIVE STAGE. Next is the PROLIFERATIVE STAGE: interstitial inflammation. Fibroblasts proliferate which causes fibrosis.
What are the histological features of DADS?
Protein rich oedema, fibrin, hyaline membranes, epithelial/fibroblast proliferation and scarring.
Name 2 granulomatous diseases.
Sarcoidosis and hypersensitivity pneumonitis.
Define sarcoidosis.
A multisystem granulomatous disorder of unknown aetiology. Hallmark feature is non-caseating granuloma. The most common of all interstitial lung diseases. A disease of temperate climates and
What are the histopathological features of sarcoidosis?
Epitheliod and giant cell granulomas. Not caused by infection. Little lymphoid inflitrate.
Which organs are commonly involved in sarcoidosis?
Lymph nodes 100%, lungs 90%, spleen 75%, liver 70%.
What is the common presentation of sarcoidosis?
In a young adult: acute arthralgia (sore joints), erythema nodosum and bilateral hilar lymphoadenopathy (CXR) - sore knees and rash on lower limbs. Can also be seen as an incidental finding on CXR. Or, SOB, cough and abnormal CXR.
What is the danger or sarcoidosis?
Infiltration of lungs and pulmonary fibrosis. Treatment (corticosteriods) is given in some cases.
How is sarcoidosis diagnosed?
Clinical findings, imaging findings (CXR), pulmonary function tests, bloods, urinalysis, ECG, TB skin test, eye exam, bronchoscopy. Surgical biopsies may be needed (mediastinoscopy/VATS).
