Biochemical markers of bone turnover in seronegative spondylarthropathy: relationship to disease activity

To investigate bone turnover in patients with seronegativespondylarthropathy, a bone formation marker, type 1 procollagen carboxy-terminal propeptide (P1CP), and resorption markers, the pyridiniumcross-links of collagen [urinary free (f) PYR and DPYR], were measured. Themedian f-PYR, f-DPYR and P1CP (+/-interquartile range) were 15.8 (6.00)nmol/mmol creatinine, 3.8 (2.2) nmol/mmol creatinine and 101.5 (38)micrograms/1, respectively. There was a positive correlation betweenresorption markers and acute-phase reactants such as C-reactive protein (r= 0.42 for PYR, r = 0.42 for DPYR, P < 0.05), and a negative correlationobserved between P1CP and the erythrocyte sedimentation rate (r = -0.64, P< 0.05). In the subgroup of patients with an elevated CRP concentration,the concentration of PYR and DPYR was significantly increased (f-PYR 25.7vs 15.8 and f-DPYR 6.6 vs 3.8, P < 0.01 for f-PYR, P < 0.05 forf-DPYR). This study suggests than an elevation in acute-phase response inpatients with seronegative spondylarthropathy is associated with increasedconcentration of bone resorption markers with a tendency for reduction inbone formation markers. This may represent uncoupling of bone formation andresorption, leading to bone loss in such patients.