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Chapter 3: Restrictive lung disorders 117

true obstructive sleep apnoea is unproven and it changes and the cysts seen in honeycomb lung. Lung
maymakefutureCPAPviaanasalmaskimpossible. function testing shows a restrictive defect (reduced lung
volumes with relatively preserved peak flows and FEV 1 .

Restrictive lung disorders Management
Treatment or removal of underlying cause. See also in-
Pulmonary fibrosis and dividual conditions.
honeycomb lung

Definition Idiopathic pulmonary fibrosis – usual
Pulmonary fibrosis is the end result of many diseases. interstitial pneumonia

Definition
Aetiology
This condition was previously known as cryptogenic
A useful mnemonic for the main causes of pulmonary
fibrosing alveolitis (CFA) characterised by interstitial in-
fibrosis is Breast Ca.
filtrates mainly in the lung bases causing progressive dys-
Bleomycin, busulphan (and other cytotoxic drugs)
pnoea. It has been reclassified as usual interstitial pneu-
Radiation
monia, a form of idiopathic interstitial pneumonia.
Extrinsic allergic alveolitis
Ankylosing spondylitis and other connective tissue
diseases (scleroderma, rheumatoid arthritis, sys- Prevalence
temic lupus erythematosus) Uncommon.
Sarcoidosis, berylliosis (exposure to this industrial al-
loy mimics sarcoidosis) Age
Tuberculosis Usually late middle age.
Cryptogenic fibrosing alveolitis (idiopathic pul-
monary fibrosis) Sex
Asbestosis Slightly M > F
The other main groups of causes are the pneumoco-
nioses, which are occupational lung diseases in response
Aetiology
to fibrogenic dusts such as coal and silicon, and drug-
Unknown, but an indistinguishable disease is seen in
induced, such as amiodarone.
association with a number of other diseases such as
asbestosis, rheumatoid arthritis and systemic sclerosis.
Pathophysiology
Antinuclear factor is positive in one third of patients
The lung has limited ability to regenerate following a se-
and rheumatoid factor is positive in 50%. Up to 75%
vere noxious insult. Fibrosis may be localised, bilateral
of patients are current or former smokers, and smoking
or widespread depending on the underlying cause. Hon-
appears to be an independent risk factor.
eycomb 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 Pathophysiology
fibrosis and subsequent respiratory failure. The alveo- There appear to be areas of fibroblast activation, which
lar wall fibrosis greatly reduces the pulmonary capillary lay down matrix, and healing of these leads to fibrosis. It
network, leading to the development of pulmonary hy- is not clear what causes the acute lung injury or the ab-
pertension, right ventricular hypertrophy, with eventual normal healing process, but increased levels of cytokines
right heart failure (cor pulmonale). and immune cells are found.

Investigations Clinical features
Chest X-ray shows reticulonodular shadowing in the Patients present with dry cough and gradually increas-
areas affected, and high-resolution CT shows reticular ing breathlessness. They may present with secondary