2021 Volume 61 Issue 4 Pages 322-326
Background. Certain malignancies are known to occasionally occur in patients with polymyositis. Conversely, the occurrence of polymyositis during the treatment of lung cancer is rare. Case. We herein report a case of polymyositis that occurred during the treatment of lung adenocarcinoma with an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI). A 58-year-old woman who was diagnosed with stage IV lung adenocarcinoma with an EGFR mutation (exon 19 deletion) received the EGFR-TKI osimertinib. During treatment, she experienced progressive pain in the proximal muscles. Laboratory findings revealed an increase in creatine kinase (CK) levels. Upon a further examination, she was diagnosed with polymyositis as a paraneoplastic syndrome. Systemic steroids, immunosuppressive agents, and immunoglobulin were administered for polymyositis, and another EGFR-TKI, afatinib, was administered for lung adenocarcinoma. Even though the clinical courses of lung cancer and polymyositis were not parallel, both disease entities subsided. Conclusion. Polymyositis during lung adenocarcinoma treatment is rare; therefore, it should be considered as a coexisting entity when such patients exhibit elevated serum CK levels.
