**4.2 Pulmonary involvement**

**4.2.1** Lung changes will occur in up to 50% of patients, and aspiration pneumonia is probably the most common finding seen on chest X-rays (Fig. 1a). Aspiration is due to cough impairment, dysfunction of the pharynx and general weakness relating to body movement (Fig. 3a). Weakness of the respiratory muscles is associated with stiffness of the lungs, small lung volumes and diaphragmatic elevation with basal plate atelectasis. The myositis may, furthermore, affect the diaphragm directly.

**4.2.2** Pulmonary arterial hypertension, with large main and proximal pulmonary arteries, may occur as a complication of interstitial lung disease, hypoventilation or vasculitis, however, may also be seen in isolation.

**4.2.3** Interstitial fibrosis was first described in 1956, is now well recognised and occurs in 5- 10% of patients (Hansell, et al., 2005). (It correlates strongly with the presence of anti-Jo-1, a myositis specific autoantibody.) The illness may be acute, rapidly fatal and resistant to therapy, or benign, indolent and asymptomatic, with favourable response to steroid treatment.

**4.2.4** The more acute patients may demonstrate airspace opacity or even widespread groundglass shadowing, with alveolar opacities earlier in the course and more likely to be steroid responsive. These changes are likely to be predominantly due to organising pneumonia.

**4.2.5** Radiographic changes often consist of symmetric reticulonodular changes, mostly in the base of the lungfields. In time the entire lungfields may be involved and a fine honeycomb pattern may form.

**4.2.6** The chest X-ray may be normal, despite the presence of confirmed clinical disease. Multifocal dystrophic pulmonary ossifications, which have been demonstrated pathologically, are not detected radiographically.

**4.2.7** High-resolution CT changes consist principally of groundglass opacification, diffuse but patchy, mostly peripheral, and also parenchymal bands and consolidation. Bronchiectasis occurs in 40% of patients, though honeycombing was uncommon. Pleural thickening and irregularity was frequently encountered.
