Objective: Pneumomediastinum (PnM), a rare complication of dermatomyositis and polymyositis (DM/PM), is sporadic and has an unclear pathogenesis. PnM is almost always associated with interstitial lung disease (ILD), and is a poor prognostic factor in inflammatory myositis patients. We studied the prevalence of PnM in Korean DM/PM and its clinical significance. Methods: We retrospectively studied the medical records of 161 patients diagnosed with DM/PM meeting Bohan-Peter's criteria at Hanyang University Hospital for Rheumatic Diseases from 1995 to 2010. We collected following findings; demographic data, diagnosis, lung involvement, cause of death, and duration from diagnosis to death.
Results: One hundred nineteen patients (73.9%) were DM and 42 patients (26.1%) were PM. Eighty three patients (51.6%) developed ILD at diagnosis or during follow up. Eighteen patients (11.2%) died because of ILD aggravation, infection, or malignancy. The mean duration from diagnosis to death was 11.5 months, with 10 patients (6.2%) dying from from ILD aggravation but none with spontaneous PnM. 6 patients (3.7%) presented with PnM, and it was associated with ILD worsening in all cases. PnM resolved with O₂ inhalation, corticosteroids, and/or immunosuppressive agents after 11 weeks (mean) of therapy
Conclusion: PnM is rare but associates with DM and aggravation of ILD. PnM does not usually cause fatalities and can be cured by appropriate therapy.

Keywords: Pneumomediastinum, Dermatomyositis/polymyositis, Interstitial lung disease, Prognosis