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

OBJECTIVES There is a lack of unanimity about (increased) serum levels of creatine kinase (CK) in patients with ankylosing spondylitis (AS), perhaps because of the inclusion of inappropriate controls. Therefore, serum levels of biochemical markers of muscle origin were assessed in AS patients compared with controls. METHODS In a comparative study serum levels of sarcoplasmic proteins indicating muscle cell leakage, creatinine, and C reactive protein (CRP) were measured. Fifty eight AS patients with a mean disease duration of 22 (SD 11) years and 58 age and sex matched controls (without back complaints) were included. RESULTS Lower serum levels in AS patients compared with controls were found for CK (mean (SD): 46 (21) v 76 (44) IU/l; p