Cryptogenic fibrosing alveolitis (CFA) / Idiopathic pulmonary fibrosis (IPF)
- Most common RLD
- Diffuse fibrosis throughout the interstitium of the lung fields
- If clear RLD = but no obvious cause: CFA/IPF
- Late-middle age (occurs in 6th decade >50).
- Progressive dyspnoea
- Gross finger clubbing
- Fine bilateral end-inspiratory crackles
- Acute interstitial pneumonitis/acute CFA = Hamman-Rich syndrome (a form of ARDS)
- Chest xray shows ground-glass appearance, progressing to obvious small nodular shadows with streaky fibrosis and honeycomb lung.
- o Irregular bilateral reticulonodular shadowing in lower zones
- High resolution CT scan
- o Characteristic changes of peripheral reticular and ground-glass opacification.
- o Seen best in the basal regions but extending over the lungs
- Respiratory function tests
- o Restrictive ventilatory defect
- o Low TLV, FEV1:FVC is normal to high = RLD!!
- o Carbon monoxide gas transfer is reduced
- Blood gases
- o Arterial hypoxaemia caused by alveolar-capillary block and ventilation-perfusion mismatch
- o Normal or low PaCO2 due to hyperventilation
- Blood tests
- o Antinuclear antibodies and rheumatoid factors +ve! (in 1/3rd of patients).
- o ESR and immunoglobulins are mildly elevated.
- Bronchoalveolar lavage
- o Increased numbers of cells, particularly neutrophils and macrophages.
- Histological confirmation
- o Transbronchial lung biopsy is rarely diagnostic but can exclude other conditions such as sarcoidosis or lymphangitis carcinomatosa.
Aetiology – cause, risk factors
Occupational exposure to metal or wood dust
Many patients show features of autoimmunity
Reported in association with:
- Coeliac disease
- Ulcerative colitis
- Renal tubular acidosis
- Primary biliary cirrhosis
Macrophages and alveolar epithelial cells are activated.
Produce growth factors:
- Platelet-derived growth factor (PDGF)
- Transforming growth factor-beta (TGF-beta)
- Insulin-like growth factor-1 (IGF-1)
Stimulate deposition of type 1 and type 3 collagens.
Histologically there are 2 main features:
- 1. Cellular infiltration with T lymphocytes and plasma cells and thickening and fibrosis of alveolar walls
- 2. Alveolitis – increased cells within the alveolar space (mainly macrophages and type II pneumocytes shed from the alveolar walls)
Treatment with prednisolone
Add Azathioprine, methotrexate or cyclophosphamide if no response – same approach as silicosis!
Median survival time is approximately 5 years = poor prognosis.