CASE 12: A SCHOOLMASTER WITH PROGRESSIVE BREATHLESSNESS

History

A 64-year-old man is referred to the respiratory outpatient clinic for assessment. He gives a history of a shortness of breath which has been insidious in onset over the last 4 years. Over the last year, this has been associated with a dry cough which he cannot seem to clear despite several courses of antibiotics. He feels fatigued and had found it more difficult to complete a round of golf, which he used to do twice a week. His weight has remained steady and he denies orthopnoea. There is no relevant past medical history. He is a non-smoker and admits to social drinking only. He takes 75 mg aspirin daily on advice of his general practitioner (GP) but is not on any other regular medication. Occupationally, he is nearing retirement as a school headmaster and denies any history of occupational dust exposure. He lives at home with his wife and keeps no pets.

Examination

On examination, he is well perfused and not cyanosed, but has evidence of nail clubbing bilaterally. Lung expansion is reduced and auscultation demonstrates fine inspiratory crackles, more marked at the bases.

Prearranged lung function studies demonstrate a restrictive lung defect and a chest radio- graph was taken for assessment (Figure 12.1).

Figure 12.1 Chest radiograph.

Questions

• How would you describe the chest radiograph appearances?

• What would be the differential for these appearances?

ANSWER 12

This is a posterior–anterior (PA) chest radiograph of an adult male patient. There is good alignment, inspiration and penetration. The heart and hila are of normal size with an ill- defined ‘shaggy’ heart boarder. The lungs demonstrate volume loss, most marked at the bases with depression of the horizontal fissure on the right. There is reticular shadowing to the lung parenchyma in a subpleural distribution with relative sparing of the apices. There is no evidence of calcified lymph nodes or air–fluid levels within the oesophagus. Correlation with old radiographs is recommended, but the appearances are suggestive of pulmonary fibrosis.

Many people have difficulty with the descriptive terms of ‘reticular’ and ‘nodular’ shad- owing. They are commonly used in chest radiograph reporting, implying clear differen- tials and distinction between infective and interstitial causes of lung disease. Reticulation describes lines that branch and interlace as a result of thickened interstitial septa between secondary pulmonary lobules. Nodularity, however, describes well-defined ‘dots’, which can vary in size and are predominantly caused by airspace opacification and imply an infective focus. Just to confuse matters, some conditions (e.g. sarcoidosis) can be both reticular and nodular in appearance.

In this scenario, the reticular pattern implies an underlying diagnosis of interstitial lung disease, with volume loss suggesting a fibrotic component. The causes of these appear- ances are numerous, and it is important to scrutinize the distribution of disease to help narrow the differential. The causes of lung fibrosis, divided between an apical and basal distribution, are listed in Table 12.1.

Table 12.1 Causes of lung fibrosis

Upper zone fibrosis Lower zone fibrosis

Allergic bronchopulmonary aspergillosis Idiopathic pulmonary fibrosis

Radiation Drugs (e.g. amiodarone)

Extrinsic allergic alveolitis Rheumatoid disease

Ankylosing spondylitis Scleroderma

Sarcoidosis Asbestosis

Silicosis Dermatomyosytis

Tuberculosis Histocytosis X

By history alone and in the absence of ancillary features associated with connective tissue disease, a diagnosis of idiopathic pulmonary fibrosis is made in this patient. To confirm and subclassify the diagnosis, the patient should be referred for a high-resolution com- puted tomography (HRCT) chest scan. This is different from a normal ‘volume’ computed tomography (CT) scan of the chest and is an unenhanced study, providing high-resolution thin (1 mm) cuts of the lung parenchyma at 1 cm intervals (Figure 12.2).

This single image of the patient’s HRCT obtained within the lower zones of the chest demonstrates areas of disruption to the normal lung parenchyma with thickening of the interlobular septa causing a ‘honeycomb’ like appearance. These changes are predomi- nantly confined to a subpleural distribution with preservation of the normal lung paren- chyma centrally. This is characteristic of usual interstitial pneumonitis (UIP), a subtype of idiopathic pulmonary fibrosis. There is clinical importance in determining the likely

subtype, as UIP is relatively insensitive to steroid therapy with a 45 per cent 5-year mor- tality.1 _{The other broad subtypes are:}

• Non-specific interstitial pneumonitis (NSIP): Despite an often normal chest radio- graph, appearances on HRCT are of patchy ground glass opacification with no clear zonal distribution. There is no evidence of honeycomb fibrosis and this subtype is more likely to respond to steroid therapy with an overall 5-year mortality of 11 per cent.1

• Desquamative interstitial pneumonitis (DIP): Seen predominantly in patients who smoke, appearances on chest radiograph and HRCT are of both subpleural ground glass opacification and honeycomb fibrosis. This is confined to the lower zones but is not associated with significant volume loss. DIP has a variable steroid response with a 50 per cent 5-year survival.1

Figure 12.2 High resolution chest CT scan.

KEY POINTS

• Reticular shadowing with parenchymal volume loss is the characteristic feature of pulmonary fibrosis on chest radiograph.

• It is important to scrutinise the distribution of disease within the lungs to help make the causative diagnosis.

• HRCT is integral in characterizing the type and extent of pulmonary fibrosis.

Reference

1. Dahnert, W. (2007) Radiology Review Manual, 6th edn. Philadelphia: Lippincott Williams and Wilkins.