Autoimmune pulmonary alveolar proteinosis during the treatment of nonspecific interstitial pneumonia complicated by clinically amyopathic dermatomyositis: A case report.

A 46-year-old male was treated with corticosteroids for nonspecific interstitial pneumonia (NSIP). He was referred to our hospital and admitted for worsening dyspnea and diffuse ground-glass opacity on chest computed tomography (CT) during corticosteroid treatment. Gottron's sign was observed, and the patient was diagnosed with clinically amyopathic dermatomyositis on skin biopsy. We increased the corticosteroid dose and added immunosuppressive agents; however, the opacity on the chest CT worsened. Based on periodic-acid-Schiff-positive granular material in the bronchoalveolar lavage fluid and the presence of anti-GM-CSF antibodies, the patient was diagnosed with autoimmune pulmonary alveolar proteinosis (APAP). The concentration of anti-GM-CSF antibodies in preserved serum was also elevated when the patient was diagnosed with NSIP. Thus, we assumed that NSIP and APAP coexisted, and that APAP manifested during immunosuppressive therapy. When exacerbation is observed during the treatment of interstitial pneumonia with immunosuppressive agents, it is necessary to consider APAP.