Background and aims Elevated serum Krebs von den Lungen-6 (KL-6) is a biomarker of interstitial pneumonia and some types of cancers. Because patients with dermatomyositis (DM) may accompany interstitial pneumonia and malignancies, serum KL-6 level has been commonly examined for patients with DM in Japan.

Methods A 62-year-old woman developed myalgia in bilateral thighs in November 2014. She was admitted to our hospital in the following month because of progressive bilateral proximal muscle weakness and myalgia, elevated serum creatine kinase (CK: 5569 U/L), and Gottron’s papule. Although muscle biopsy had not been done, the diagnosis as DM was further supported by muscle MRI, electromyogram and skin biopsy. The body CT revealed pelvic mass with ascites, but not interstitial pneumonia.

Results Although prednisolone 50 mg/day and intravenous immunoglobulin therapy against progressive muscle weakness including severe dysphagia only showed a partial response, the surgical resection of ovarian mass, identified as ovarian serous adenocarcinoma stage II c, followed by chemotherapy resulted in clinical remission of DM. Serum KL-6 level, as well as CA-125 decreased below the upper normal limit.

Conclusions The present case suggests that the measurement of serum KL-6 may be useful in the evaluation of patients with DM.