Pulmonary fibrosis describes a group of diseases which produce interstitial lung damage and can ultimately lead to:
- Fibrosis (scarring) of the lung tissue
- Restrictive pattern in lung function tests - Fev1/FVC ratio is greater than 80%
- Formation of cystic spaces, leading to 'honeycomb lung' appearance.
Pulmonary fibrosis may be associated with a known cause (i.e. occupational lung disease), due to systemic illness (i.e. sarcoidosis) or idiopathic.
The key presenting features of pulmonary fibrosis can be recognised as the Four D's:
- Dry cough
- Diffuse inspiratory crackles
- Digital clubbing
Other symptoms may vary depending on the causative condition.
Conditions Causing Pulmonary Fibrosis
Idiopathic Pulmonary Fibrosis
This is a relatively rare type of idiopathic interstitial pneumonia, but is the most common cause of interstitial lung disease. It is known to also affect the lower lung lobes. Important extra-pulmonary symptoms include fatigue and sometimes considerable weight loss. Patients are at an increased risk of lung cancer. Investigations: IPF is a diagnosis made when all other causes of pulmonary fibrosis are excluded. FBC may indicate mild anaemia or raised ESR, whilst CXR will display bilateral basal and peripheral infiltrates.
Conditions under this umbrella include:
- Coal worker's pneumoconiosis: related to inhalation of coal dust over 15–20 years. In progressive massive fibrosis, round fibrotic nodules may present, which can become infected with TB, resulting in severe emphysema, sepsis and the production of black sputum. The combination of coal worker's pnemoconiosis and rheumatoid arthritis is known as Caplan's Syndrome.
- Asbestosis: caused by long term inhalation of asbestos fibres usually encountered at construction sites or in old buildings. Presentation is similar to other fibrotic lung conditions, with progressive dyspnoea, fine inspiratory crackles and digital clubbing. Asbestosis can cause pleural plaques and increases a patient's risk of developing malignant mesothelioma or bronchial adenocarcinoma.
- Extrinsic Allergic Alveolitis: Otherwise known as 'hypersensitivity pneumonitis', this is caused by inhalation of allergens by sensitised individuals, provoking a widespread inflammatory reaction. Conditions specific to certain allergens include Farmer's Lung (mould in hay), Bird-fancier's lung (bird droppings) and Bagassosis (sugar cane).
See article on sarcoidosis.