Sarcoid Myositis with Anti-Ku Antibody Consistent with both Sarcoidosis and Polymyositis

We herein describe a case of sarcoid myositis with anti-Ku antibody positivity. Pathological findings of the muscle were compatible with sarcoidosis, but could not be completely distinguished from myositis diseases that arise from other causes. According to a physical examination, pathological findings, the detection of anti-Ku antibody and the human leukocyte antigen (HLA)-DPB1 allele, we strongly suspected that the patient developed both sarcoidosis and polymyositis. Sarcoidosis is often complicated by autoimmune diseases. This case suggests the possibility that sarcoidosis and other autoimmune diseases may have common causal genetic factors.