title: MR-defined fat infiltration of the lumbar paravertebral muscles differs between non-radiographic axial spondyloarthritis and established ankylosing spondylitis.
abstract: OBJECTIVE
  The aim of our study was to compare the magnetic resonance imaging (MRI)-defined cross-sectional area and semi-quantitative grading of fatty degeneration of lumbar paravertebral muscles in patients with non-radiographic axial spondyloarthritis (nr-axSpA) and established ankylosing spondylitis (AS).
  
  
  METHODS
  Cross-sectional area (CSA) of lumbar paravertebral muscles, including the right and left multifidus (MF), erector spina (ES), psoas (PS), vertebral body and muscle:vertebra ratio (MVr), was measured. Fat infiltration of the paravertebral muscles was graded semi-quantitatively.
  
  
  RESULTS
  The CSA of the MF, ES and PS muscles and the MVr (at the L2, L3, L4 and L5 levels) were quite similar between patients with nr-axSpA (n = 14) and AS (n = 22). However, patients with AS had higher grades of fat infiltration than those with nr-axSpA (Right L4 grading of MF + ES muscles: 1.4 ± 0.73 vs. 0.51 ± 0.52, respectively, p = 0.001; left L4 grading: 1.36 ± 0.65 vs. 0.38 ± 0.50, respectively, p < 0.0001). This difference remained significant after adjusting for age and symptom duration. The inter-rater reliability was good (intraclass correlation coefficient 0.75 and 0.85).
  
  
  CONCLUSIONS
  This is first study demonstrating that MRI-defined fatty degeneration differs between patients with nr-axSpA and established AS. Semi-quantitative grading is reliable, and fatty degeneration of paravertebral muscles seems to be related to chronicity and spinal functions in patients with nr-axSpA and AS.
authors.affiliation: Division of Rheumatology, Department of PMR, Faculty of Medicine, Gevher Nesibe Hospital, Erciyes University, 38039 Kayseri, Turkey. ozgur.akgul.md@gmail.com
authors.forename: Ozgur
authors.initials: O
authors.lastname: Akgul
authors.forename: Arif
authors.initials: A
authors.lastname: Gulkesen
authors.forename: Gurkan
authors.initials: G
authors.lastname: Akgol
authors.forename: Salih
authors.initials: S
authors.lastname: Ozgocmen
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D000328:Adult; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae; D008161:Lumbosacral Region / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D064170:Paraspinal Muscles / Q000473:pathology*; D015203:Reproducibility of Results; D025241:Spondylarthritis / Q000473:pathology*; D013167:Spondylitis, Ankylosing / Q000473:pathology*