A potential clinical usefulness of measuring serum bilirubin levels in patients with polymyositis.

OBJECTIVE Accumulated data have indicated that bilirubin has antiinflammatory, antioxidative, and immunosuppressive properties. Polymyositis (PM) belongs to an autoimmune disease characterized by chronic inflammation in skeletal muscle. Until now, to the best of our knowledge, there are no literature investigating bilirubin levels in patients with PM. Therefore, the aim of this investigation was to assess a relationship between bilirubin and PM. PATIENTS AND METHODS Our study included newly diagnosed 77 patients with PM who were admitted to the Affiliated Hospital of Youjiang Medical University for Nationalities (Guangxi, China) and 108 healthy subjects as controls. Clinical characteristics and laboratory parameters of patients were analyzed, retrospectively. RESULTS The serum concentrations of total bilirubin (TB), conjugate bilirubin (CB), unconjugated bilirubin (UCB) were significantly lower in patients with PM than healthy controls. Serum concentrations of TB were negatively correlated with erythrocyte sedimentation rate (ESR), creatine kinase (CK) and lactic dehydrogenase (LDH) in patients with PM (r=-0.494, p<0.001; r=-0.274, p=0.017; r=-0.282, p=0.014), and serum concentrations of UCB were negatively correlated with ESR and CK in PM patients (r=-0.424, p<0.001; r=-0.234, p=0.041). Both serum TB and UBC concentrations were positively correlated with manual muscle test (MMT) score in patients with PM (r=0.328, p=0.004; r=0.333, p=0.004). In multiple linear regression analysis, serum UBC levels were independently associated with MMT score (r=0.239, p=0.003). CONCLUSIONS We observed significantly lower serum concentrations of TB, CB and UCB in patients with PM, and suggested a potential association between serum concentrations of UBC and disease activity in PM patients.