Significant loss of bone mass in patients with early, active ankylosing spondylitis - A followup study

Objective, To analyze whether inflammatory disease activity plays a substan tial role in the loss of bone mass observed in ankylosing spondylitis (AS) patients who have not yet developed ankylosis. Methods. A longitudinal cohort study of 34 patients with early AS (duration <10 years) without ankylosis was conducted. The mean followup was 19 month s. Loss of bone mass in defined regions of the lumbar spine and femoral nec k was analyzed by dual x-ray absorptiometry, Patients were grouped accordin g to biologic parameters of disease activity (erythrocyte sedimentation rat e or C-reactive protein level). Group 1 consisted of 14 patients with activ e disease; group 2 comprised 20 patients with inactive disease, Serum level s of interleukin-6 (IL-6) and of hormones (sex, thyroid, and calciotropic), vertebral mobility (Schober test), daily physical activity, and treatment administered were recorded every 6 months for all patients. Results, At the end of the followup period, patients with active AS showed a significant reduction in bone mass in the lumbar spine (mean 1.01 gm/cm(2 ) at study entry versus 0.961 gm/cm(2) at followup [P = 0.005]) and femoral neck (0.849 gm/cm(2) versus 0.821 gm/cm(2) [P = 0.015]), which represented losses of 5% and 3%, respectively. In contrast, no significant reduction i n bone mass was observed in patients with inactive AS, As expected, serum I L-6 levels were significantly higher in patients with active AS than in tho se with inactive disease (mean +/- SD 8.3 +/- 9 pg/ml versus 2.8 +/- 5 pg/m l [P = 0.008]). No significant differences were observed between the 2 grou ps in any of the other variables analyzed. Conclusion. The observation that loss of bone mass in AS occurred only in p atients with persistent active disease strongly suggests that inflammatory activity of the disease itself plays a major role in the pathophysiology of the early bone mineral disorders observed in these patients.