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What constitutes the fat signal detected by MRI in the spine of patients with ankylosing spondylitis? A prospective study based on biopsies obtained during planned spinal osteotomy to correct hyperkyphosis or spinal stenosis
  1. Xenofon Baraliakos1,
  2. Heinrich Boehm2,
  3. Reza Bahrami2,
  4. Ahmed Samir2,3,
  5. Georg Schett4,
  6. Markus Luber4,
  7. Andreas Ramming4,
  8. Juergen Braun1
  1. 1 Rheumazentrum Ruhrgebiet, Ruhr-University Bochum, Herne, Germany
  2. 2 Department for Spinal Surgery, Zentralklinik Bad Berka, Bad Berka, Germany
  3. 3 Orthopedics and Trauma Department, Cairo University, Cairo, Egypt
  4. 4 Department of Internal Medicine 3 - Rheumatology and Immunology, Friedrich-Alexander-University (FAU) Erlangen-Nürnberg and Universitätsklinikum Erlangen, Erlangen, Erlangen, Germany
  1. Correspondence to Associate Professor Dr. Xenofon Baraliakos, Rheumazentrum Ruhrgebiet, Ruhr-University Bochum, Herne 44649, Germany; xenofon.baraliakos{at}


Objective Study the MRI signal of fatty lesions (FL) by immunohistological analysis of vertebral body biopsies of patients with ankylosing spondylitis (AS) compared with degenerative disc disease (DDD).

Methods Biopsies obtained during planned surgery from vertebral edges where MRI signals of FL was detected were stained with H&E. Immunofluorescence (IF) staining was performed to quantify osteoblasts and osteoclasts. Bone marrow (BM) composition, grade of cellularity and quantification of cells were analysed on six randomly chosen high-power fields (HPF; 0.125 mm2) at 200-fold magnification per patient by two experienced researchers in a blinded manner.

Results Biopsies of 21 patients with AS and 18 with DDD were analysed. Adipocytes were found in the BM of 19 patients with AS (90.5%) versus 5 with DDD (27.8%) (p<0.001), while inflammatory infiltrates were found in in the BM of 8 patients with AS (38.1%) versus 14 with DDD (77.8%) (p=0.035) and fibrosis in 6 patients with AS (28.6%) versus 4 with DDD (22.2%) (p=n .s.). The most frequently detected cells were adipocytes in AS (43.3%) versus DDD (16.1%, p=0.002) and inflammatory mononuclear cells in DDD (55%) versus AS (11.0%, p=0.001). Using IF staining, there was more osteoblastic than osteoclastic activity (6.9 vs 0.17 cells/HPF) in FL as compared with inflammatory BM (1.3 vs 7.4 cells/HPF), respectively.

Conclusion MRI FL correspond to presence of adipocytes, resulting to change of cellular homeostasis towards diminution of osteoclasts in the BM of patients with AS. The cross-talk between the different cell types and osteitis, fat and new bone formation needs further study.

  • axial spondyloarthritis
  • magnetic resonance imaging
  • fatty lesions
  • biopsy

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  • Handling editor Josef S Smolen

  • Contributors XB and JB: concept, coordination of the study, data analysis, data interpretation, writing of the manuscript. HB, RB and AS: collection of biopsies, data interpretation and editing of the manuscript. GS, ML and AR: immunohistological analyses, data interpretation and editing of the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Ethics approval The study was approved by the Ethical Committee of the Ruhr-University Bochum, Germany (Reg. Nr. 4360-12).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement The exact steps of all analyses, including the tissue analyses, are included in the manuscript. For additional information, please contact the corresponding author.