Interstitial lung disease includes many conditions that cause inflammation and fibrosis of the lung parenchyma (lung tissue). Fibrosis involves the replacement of elastic and functional lung tissue with non-functional scar tissue.
The conditions we will cover here are::
- Idiopathic pulmonary fibrosis (the most important to remember)
- Secondary pulmonary fibrosis
- Hypersensitivity pneumonitis
- Cryptogenic organising pneumonia
- Asbestosis
Presentation
The key presenting features are:
- Shortness of breath on exertion
- Dry cough
- Fatigue
Patients with idiopathic pulmonary fibrosis have typical findings on examination:
- Bibasal fine end-inspiratory crackles
- Finger clubbing
TOM TIP: Remember clubbing and bibasal fine inspiratory crackles in idiopathic pulmonary fibrosis. These patients are ideal for OSCEs as they are stable and have good signs.
Diagnosis
Diagnosis of interstitial lung disease involves:
- Clinical features
- High-resolution CT scan (HRCT) of the thorax (showing a typical “ground glass” appearance)
- Spirometry
Spirometry may be normal or show a restrictive pattern:
- FEV1 and FVC are equally reduced
- FEV1:FVC ratio greater than 70%
Other investigations where there is doubt about the diagnosis include:
- Lung biopsy
- Bronchoalveolar lavage
General Management
Generally, there is a poor prognosis and limited management options in interstitial lung disease, and treatment is primarily supportive. Options include:
- Remove or treat the underlying cause
- Home oxygen where there is hypoxia
- Stop smoking
- Physiotherapy and pulmonary rehabilitation
- Pneumococcal and flu vaccine
- Advanced care planning and palliative care where appropriate
- Lung transplant is an option, but the risks and benefits need careful consideration
Idiopathic Pulmonary Fibrosis
Idiopathic pulmonary fibrosis features progressive pulmonary fibrosis with no apparent cause. It presents with an insidious onset of shortness of breath and dry cough over more than 3 months. It usually affects adults over 50 years old. The prognosis is poor, with a 2-5 years life expectancy from diagnosis.
Two medications are licensed that can slow the progression of the disease:
- Pirfenidone reduces fibrosis and inflammation through various mechanisms
- Nintedanib reduces fibrosis and inflammation by inhibiting tyrosine kinase
Secondary Pulmonary Fibrosis
Several drugs can cause pulmonary fibrosis:
- Amiodarone (also causes grey/blue skin)
- Cyclophosphamide
- Methotrexate
- Nitrofurantoin
Pulmonary fibrosis can occur secondary to other conditions:
- Alpha-1 antitrypsin deficiency
- Rheumatoid arthritis
- Systemic lupus erythematosus (SLE)
- Systemic sclerosis
- Sarcoidosis
Hypersensitivity Pneumonitis
Hypersensitivity pneumonitis, also called extrinsic allergic alveolitis, involves type III and type IV hypersensitivity reaction to an environmental allergen. Inhalation of allergens in patients sensitised to that allergen causes an immune response, leading to inflammation and damage to the lung tissue.
Bronchoalveolar lavage is performed during a bronchoscopy procedure. The airways are washed with sterile saline to gather cells, after which the fluid is collected and analysed. Raised lymphocytes (lymphocytosis) are suggestive of hypersensitivity pneumonitis.
Management involves removing the allergen, oxygen where necessary and steroids.
Examples of specific causes:
- Bird-fancier’s lung is a reaction to bird droppings
- Farmer’s lung is a reaction to mouldy spores in hay
- Mushroom worker’s lung is a reaction to specific mushroom antigens
- Malt worker’s lung is a reaction to mould on barley
Cryptogenic Organising Pneumonia
Cryptogenic organising pneumonia was previously known as bronchiolitis obliterans organising pneumonia. It involves a focal area of inflammation of the lung tissue. It can be idiopathic or triggered by infection, inflammatory disorders, medications, radiation, environmental toxins, or allergens.
Presentation is similar to infectious pneumonia, with shortness of breath, cough, fever and lethargy. Inspiratory crackles may be heard on auscultation.
Chest x-ray findings are also similar to pneumonia, with a focal consolidation. A lung biopsy is the definitive investigation. Diagnosis is often delayed due to the similarities to infectious pneumonia.
Treatment is with systemic corticosteroids.
Asbestosis
Asbestosis refers to lung fibrosis related to asbestos exposure. Asbestos is fibrogenic, meaning it causes lung fibrosis. It is also oncogenic, meaning it causes cancer. The effects of asbestos usually take several decades to develop. Asbestos inhalation causes several problems:
- Lung fibrosis
- Pleural thickening and pleural plaques
- Adenocarcinoma
- Mesothelioma
Patients may be eligible for compensation if they develop asbestos-related health conditions. All deceased patients with occupational asbestos exposure must be referred to the coroner.
Last updated June 2023
Now, head over to members.zerotofinals.com and test your knowledge of this content. Testing yourself helps identify what you missed and strengthens your understanding and retention.
