Dermatomyositis and polymyositis are associated with the development of antibodies to nuclear and cytoplasmic antigens. One group of these autoantibodies, the antisynthetases, is associated with interstitial lung disease (80% of the patients with associated interstitial lung disease have these autoantibodies).  The most common antisynthetase antibody is Anti-Jo1, which was positive in this patient.

Antisythetase lung disease results in a nonspecific diffuse interstitial lung disease with superimposed consolidations from organizing pneumonia.

The 5-year mortality rate in one series of 182 patients who had dermatomyositis followed in Japan was 27%. The most common causes of death were malignancy and interstitial lung disease.