Evaluation of Changes in Peri-Pelvic Musculature in Ankylosing Spondylitis Using mDixon-Quant and T2 Mapping.

RATIONALE AND

OBJECTIVES

This study employed mDixon-Quant and T2 mapping to assess quantitative changes in peri-pelvic muscles in patients with ankylosing spondylitis (AS).

MATERIALS AND

METHODS

Between June 2023 and July 2024, 60 patients with ankylosing spondylitis (AS group) and 46 healthy controls matched for age, gender, and body mass index (BMI) underwent routine MRI of the sacroiliac joints as well as mDixon-Quant and T2 mapping. Fat fraction (FF) and T2 values were measured in the gluteus maximus (Gmax), gluteus medius (Gmed), gluteus minimus (Gmin), and iliopsoas muscles. Clinical data (disease duration, ESR, CRP) and disease activity scores (BASDAI, ASDAS) were recorded. Inter-reader agreement was assessed using the intraclass correlation coefficient (ICC). Group differences and correlations were evaluated using ANOVA and Spearman's rank correlation, respectively.

RESULTS

AS patients exhibited significantly higher FF values in all assessed peri-pelvic muscles, with the most pronounced elevation in the Gmax (P < 0.05). Iliopsoas T2 values were elevated in the AS group (P < 0.05), whereas no significant differences were observed in Gmed, Gmin, or Gmax T2 values. FF values were higher in patients with grade III/IV sacroiliitis than in those with grade I/II; additionally, grade IV patients showed elevated Gmed T2, and grade III patients showed elevated iliopsoas T2 (P < 0.05). FF of the bilateral Gmax and left Gmin correlated positively with disease duration and ASDAS, while right iliopsoas FF correlated with BASDAI (P < 0.05). No significant correlations were found between T2 values and clinical indices.

CONCLUSION

mDixon-Quant enables reliable, non-invasive quantitative assessment of peri-pelvic muscle fatty infiltration in patients with AS, whereas T2 mapping shows limited additional value in this clinical context.