Correlation analysis. Relationships between serum creatinine level and body weight (A), creatine phosphokinase and arthritis score (B), change in body weight and arthritis score (C), and serum creatinine level and arthritis score (D). Pearson’s correlation coefficients between the parameters (arthritis score, serum creatinine, serum CPK, and body weight) were calculated. The concentration of serum creatinine, a marker to reflect muscle mass, was positively correlated with body weight (A). CPK levels were not well related with arthritis score (B), but arthritis score showed a weak correlation with body weight change (C). Arthritis score showed a strong correlation with creatinine levels (D).