Progression of Interstitial Lung Disease Upon Overlapping of Systemic Sclerosis with Polymyositis

We describe a 73-year-old woman with systemic sclerosis (SSc)-polymyositis (PM) overlap syndrome, primarily SSc followed by PM. She had suffered from SSc and had interstitial pneumonia (IP), which was stable. Eight years after the initial diagnosis of SSc, proximal muscle weakness, myalgia, and dyspnea on effort developed. A chest computed tomography (CT) showed reticular shadows, and serum markers of IP such as KL-6 and surfactant protein-D were elevated at 1,170 U/mL and 176 ng/mL, respectively. Bronchoalveolar lavage fluid showed a remarkably increased number of lymphocytes. Exacerbation of SSc-IP 8 years after the initial diagnosis of SSc is not usual, and a marked increase in the number of lymphocytes in bronchoalveolar lavage fluid is also uncommon in SSc-IP, indicating overlap of another connective tissue disease. The diagnostic criteria for PM were satisfied; thus, SSc-PM overlap syndrome was diagnosed. We emphasize the need to investigate whether another connective tissue disease has developed when symptoms or laboratory findings cannot be explained by the usual clinical course of an existing connective tissue disease.