Osteoporosis in ankylosing spondylitis - prevalence, risk factors and methods of assessment
1 Department of Rheumatology and Inflammation Research, Sahlgrenska Academy at University of Gothenburg, Guldhedsgatan 10A, S-413 46 Göteborg, Sweden
2 Centre for Bone and Arthritis Research, Institute of Medicine, Sahlgrenska Academy at University of Gothenburg, Sahlgrenska University Hospital, Vita stråket 11, S-413 45 Göteborg, Sweden
3 Centre for Medical Imaging and Physiology, Skåne University Hospital, Lund University, Getingevägen 4, S-221 85 Lund, Sweden
4 Department of Radiology, Sahlgrenska University Hospital/Mölndal, Göteborgsvägen 31, S-431 30 Mölndal, Sweden
5 Department of Rheumatology, Alingsås Lasarett, Södra Ringgatan 30, S-441 83 Alingsås, Sweden
6 Department of Rheumatology, SÄS Borås, Brämhultsvägen 53, S-501 82 Borås, Sweden
Arthritis Research & Therapy 2012, 14:R108 doi:10.1186/ar3833Published: 8 May 2012
Osteoporosis can be a complication of ankylosing spondylitis (AS), but diagnosing spinal osteoporosis can be difficult since pathologic new bone formation interferes with the assessment of the bone mineral density (BMD). The aims of the current study were to investigate prevalence and risk factors for reduced BMD in a Swedish cohort of AS patients, and to examine how progressive ankylosis influences BMD with the use of dual-energy x-ray absorptiometry (DXA) of the lumbar spine in different projections.
Methods of assessment were questionnaires, back mobility tests, blood samples, lateral spine radiographs for syndesmophyte grading (mSASSS), DXA of the hip, radius and lumbar spine in anteroposterior (AP) and lateral projections with estimation of volumetric BMD (vBMD).
AS patients (modified New York criteria), 87 women and 117 men, mean age 50 ± 13 years and disease duration 15 ± 11 years were included. According to World Health Organization (WHO) criteria 21% osteoporosis and 44% osteopenia was diagnosed in patients > = 50 years. Under age 50 BMD below expected range for age was found in 5%. Interestingly lateral lumbar DXA showed significantly lower BMD and revealed significantly more cases with osteoporosis as compared with AP DXA. Lumbar vBMD was not different between sexes, but women had significantly more lumbar osteoporosis measured with AP DXA (P < 0.001). Men had significantly higher mSASSS (P < 0.001). Low BMD was associated with high age, disease duration, mSASSS, Bath Ankylosing Spondylitis Metrology Index (BASMI), inflammatory parameters and low body mass index (BMI). Increasing mSASSS correlated significantly with decreasing lateral and volumetric lumbar BMD, while AP lumbar BMD showed tendency to increase.
Osteoporosis and osteopenia is common in AS and associated with high disease burden. Lateral and volumetric lumbar DXA are more sensitive than AP DXA in detecting osteoporosis and are less affected by syndesmophyte formation.