Restrictive lung disorders
Pulmonary fibrosis and honeycomb lung
Pulmonary fibrosis is the end result of many diseases.
A useful mnemonic for the main causes of pulmonary fibrosis is Breast Ca.
· Bleomycin, busulphan (and other cytotoxic drugs) Radiation
· Extrinsic allergic alveolitis
· Ankylosing spondylitis and other connective tissue diseases (scleroderma, rheumatoid arthritis, systemic lupus erythematosus)
· Sarcoidosis, berylliosis (exposure to this industrial alloy mimics sarcoidosis)
· Cryptogenic fibrosing alveolitis (idiopathic pulmonary fibrosis)
The other main groups of causes are the pneumoconioses, which are occupational lung diseases in response to fibrogenic dusts such as coal and silicon, and drug-induced, such as amiodarone.
The lung has limited ability to regenerate following a severe noxious insult. Fibrosis may be localised, bilateral or widespread depending on the underlying cause. Honeycomb lung represents late-stage fibrosis. Patients are at an increased risk of secondary infection and even if the original insult is removed may develop progressive fibrosis and subsequent respiratory failure. The alveolar wall fibrosis greatly reduces the pulmonary capillary network, leading to the development of pulmonary hypertension, right ventricular hypertrophy, with eventual right heart failure (cor pulmonale).
Chest X-ray shows reticulonodular shadowing in the areas affected, and high-resolution CT shows reticular changes and the cysts seen in honeycomb lung. Lung function testing shows a restrictive defect (reduced lung volumes with relatively preserved peak flows and FEV1.
Treatment or removal of underlying cause. See also individual conditions.