The prevalance of osteoporosis and fractures in ankylosing spondylitis and its association with HLA-B27 status and clinical activity

Purpose: Bone loss is a well-known feature of inflammatory arthritides including Ankylosing spondylitis(AS). However, bone loss measured by Dual-energy x-ray absorpsiometry (DEXA) can be masked due to syndesmphytes in AS. In this study we aimed to investigate the association between the prevalence of osteoporosis and compression fractures and HLA-B27 status, clinical and laboratory activity and to determine the method of measurement best reflecting bone loss.Materials and methods: Eighty-six patients with AS and 50 control patients were included to our study. Bone mineral measurements of PA and lateral spine and hips of patients and controls were carried out with DEXA method. HLA-B27 status of patients was recruited from patients? records. AS patients were grouped into two according to each of these parameters; disease stage, disease activity, presence of osteoporosis, presence of syndesmofites and fractures and then subgroup analyses with regard to bone loss were performed. BASDAİ, BASMİ, BASFİ and BASRİ were used for disease activity, limitation of mobilization, functional status and radiological involvement respectively.Results: Sixty-nine(80.2%) AS patients and 35(70.0%) control patients were male. PA spinal BMD was not significantly different between patients and controls, however hip BMD and lateral spinal BMD values were significantly lower in patient group. Although not statistically significant, bone loss according to femoral and lateral spinal DEXA values were greater in late stage AS patients when compared to early stage patients. PA spinal measures, on the contrary, showed greater bone loss in early AS patients. Low body mass index, high BASMI and BASFI scores and high erythrocytes sedimentation rate were found as factors associated with osteoporosis in AS patients. Compression fractures were present in 28% of patients. Presence of sindesmofit, presence of osteoporosis according to femoral and lateral spinal BMD values, age, diagnostic delay, high BASMİ and BASRİ scores were found as factors associated with the presence of fractures. Osteoporosis rate in spine, hip or any site of measurement were higher in HLA-B27+ patients when compared to HLA-B27- patients, however this difference did not reach a statistically significant point.Conclusion: Bone loss is more increased in AS patients than in controls. Although PA spinal BMD measurement can disclose bone loss correctly in early AS, bone loss can be masked due to sindesmofites in late AS patients. BMD measured by lateral spinal projection reflects increased bone loss and risk of fractures more correctly/properly than PA spinal and femoral measures. Bone loss and risk of fracture do not change with the HLA-B27 status.