Decreased serum biochemical markers of muscle origin in patients with ankylosing spondylitis

Objectives-There is a lack of unanimity about (increased) serum levels of c reatine kinase (CK) in patients with ankylosing spondylitis (AS), perhaps b ecause of the inclusion of inappropriate controls. Therefore, serum levels of biochemical markers of muscle origin were assessed in AS patients compar ed with controls. Methods-In a comparative study serum levels of sarcoplasmic proteins indica ting muscle cell leakage, creatinine, and C reactive protein (CRP) were mea sured. Fifty eight AS patients with a mean disease duration of 22 (SD 11) y ears and 58 age and sex matched controls (without back complaints) were inc luded. Results-Lower serum levels in AS patients compared with controls were found for CK (mean (SD): 46 (21) v 76 (44) IU/l; p<0.001), aldolase (0.43 (0.36) v 0.58 (0.32) IU/l; p=0.001), creatinine (91 (13) v 96 (11) mu mol/l; p=0. 02), alanine aminotransferase (2.8 (1.5) v 4.1 (2.9) IU/l; p=0.001) and asp artate aminotransferase (7.0 (2.7) v 8.4 (3.5) IU/l; p=0.02). Also the lean body mass, as estimated by a formula using height, weight, age and sex, sh owed lower values in patients versus controls (56 (9) v 59 (9) kg; p=0.004) , but creatinine clearance (by Cockcroft and Gault formula) was not differe nt (p=0.48). Partial correlation coefficients adjusted for age and sex show ed that CRP levels correlated negatively with CK and aldolase levels in AS patients (r=-0.48, p<0.001 and r=-0.37, p=0.005, respectively). Conclusion-Serum levels of biochemical markers of muscle origin were lower in AS patients compared with controls. Patients with active AS, as reflecte d by high CRP levels, may have an increased protein degradation, predominan tly in skeletal muscle.