Polymyositis (pulmonary manifestations)

Lung involvement in polymyositis can have a number of manifestations including those resembling interstitial lung disease.

For a general discussion of polymyositis, please refer to the parent article.

Radiographic features

The lungs may present with a mixture of different fibrotic patterns, e.g. UIP or NSIP patterns, with the latter considered commoner. Cryptogenic organizing pneumonia (COP) pattern of pulmonary consolidations may be present simultaneously ⁷.

Plain radiograph

The frequency of a radiographic parenchymal abnormality in an individual with polymyositis is low (ranges around 5%). If present and not complicated with any other problem, it is usually appreciated as asymmetrical basal predominant reticular pattern which can progress to being more diffuse with time. Areas of consolidation (often bilateral) may develop in some patients.

Some patients may have an elevated diaphragm from diaphragmatic paralysis.

CT

Initial findings

Initial CT findings of pulmonary involvement in patients can include:

• considered characteristic and reversible CT findings ²
  • patchy consolidation
  • parenchymal bands
  • irregular peribronchovascular thickening
• other findings
  • prominent interlobular septa
  • ground-glass attenuation
  • subpleural lines

Later findings

• honeycombing: may develop in some patients

A proportion of patients may have a pattern somewhat resembling that of cryptogenic organizing pneumonia.

Differential diagnosis

Imaging features can often overlap pulmonary manifestations of dermatomyositis.