title: Higher bone turnover is related to spinal radiographic damage and low bone mineral density in ankylosing spondylitis patients with active disease: a cross-sectional analysis.
abstract: BACKGROUND
  Ankylosing spondylitis (AS) is characterized by excessive bone formation and bone loss. Our aim was to investigate the association of bone turnover markers (BTM) with spinal radiographic damage and bone mineral density (BMD) in AS patients with active disease.
  
  
  METHODS
  201 consecutive AS outpatients of the Groningen Leeuwarden AS (GLAS) cohort were included. Serum markers of bone resorption (C-telopeptides of type-I collagen, sCTX) and bone formation (procollagen type-I N-terminal peptide, PINP; bone-specific alkaline phosphatase, BALP) were measured. Z-scores were used to correct for the normal influence that age and gender have on bone turnover. Radiographs were scored by two independent readers according to modified Stoke AS Spinal Score (mSASSS). The presence of complete bridging (ankylosis of at least two vertebrae) was considered as measure of more advanced radiographic damage. Low BMD was defined as lumbar spine and/or hip BMD Z-score ≤ -1.
  
  
  RESULTS
  Of the 151 patients with complete data, 52 (34%) had ≥ 1 complete bridge, 49 (33%) had ≥ 1 syndesmophyte (non-bridging), and 50 (33%) had no syndesmophytes. 66 (44%) had low BMD. Patients with bridging had significantly higher sCTX and PINP Z-scores than patients without bridging (0.43 vs. -0.55 and 0.55 vs. 0.04, respectively). Patients with low BMD had significantly higher sCTX Z-score than patients with normal BMD (-0.08 vs. -0.61). After correcting for gender, symptom duration, and CRP, sCTX Z-score remained significantly related to the presence of low BMD alone (OR: 1.60), bridging alone (OR: 1.82), and bridging in combination with low BMD (OR: 2.26).
  
  
  CONCLUSIONS
  This cross-sectional study in AS patients with active and relatively long-standing disease demonstrated that higher serum levels of sCTX, and to a lesser extent PINP, are associated with the presence of complete bridging. sCTX was also associated with low BMD. Longitudinal studies are needed to confirm that serum levels of sCTX can serve as objective marker for bone-related outcome in AS.
authors.affiliation: Rheumatology and Clinical Immunology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands; Rheumatology, Medical Center Leeuwarden, Leeuwarden, The Netherlands.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Arends
authors.affiliation: Rheumatology and Clinical Immunology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Anneke
authors.initials: A
authors.lastname: Spoorenberg
authors.affiliation: Rheumatology, Medical Center Leeuwarden, Leeuwarden, The Netherlands.
authors.forename: Monique
authors.initials: M
authors.lastname: Efde
authors.affiliation: Rheumatology, Medical Center Leeuwarden, Leeuwarden, The Netherlands.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Bos
authors.affiliation: Rheumatology and Clinical Immunology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Martha K
authors.initials: MK
authors.lastname: Leijsma
authors.affiliation: Rheumatology and Clinical Immunology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Hendrika
authors.initials: H
authors.lastname: Bootsma
authors.affiliation: Epidemiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Nic J G M
authors.initials: NJ
authors.lastname: Veeger
authors.affiliation: Rheumatology and Clinical Immunology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Brouwer
authors.affiliation: Laboratory Medicine, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Eveline
authors.initials: E
authors.lastname: van der Veer
mesh_terms: D000328:Adult; D015519:Bone Density / Q000502:physiology*; D001862:Bone Resorption / Q000503:physiopathology; D024042:Collagen Type I / Q000097:blood; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000502:physiology*; D008297:Male; D010012:Osteogenesis / Q000502:physiology*; D010446:Peptide Fragments / Q000097:blood; D010455:Peptides / Q000097:blood; D011347:Procollagen / Q000097:blood; D011832:Radiation Injuries / Q000097:blood / Q000503:physiopathology*; D011859:Radiography / Q000009:adverse effects*; D013167:Spondylitis, Ankylosing / Q000000981:diagnostic imaging* / Q000503:physiopathology*
chemical_list: D024042:Collagen Type I; D010446:Peptide Fragments; D010455:Peptides; D011347:Procollagen; C052929:collagen type I trimeric cross-linked peptide; C047202:procollagen Type I N-terminal peptide