Malignant Peritoneal Mesothelioma Presenting with Polymyalgia Rheumatica-like Syndrome

A 30-year-old man was admitted to our hospital because of pain in his proximal extremities. The pain mimicked polymyalgia rheumatica (PMR) and it temporarily improved by a low dose of glucocorticoids, but his symptoms relapsed many times. After six years of glucocorticoid treatment, he developed abdominal pain and ascites, for which he was diagnosed with malignant peritoneal mesothelioma (MPM). His PMR-like symptoms improved with cytoreductive surgery and chemotherapy for MPM. Finally, we diagnosed this PMR-like syndrome to be paraneoplastic syndrome with MPM. Although cases of MPM complicated by PMR-like syndrome are rare, MPM should be taken into account in the differential diagnosis.