T2 mapping and fat quantification of lumbar paraspinal muscle in ankylosing spondylitis: a case control study

BACKGROUND: To compare changes in the composition of paraspinal muscles of patients with ankylosing spondylitis (AS) and matched healthy controls using T2 mapping and T2 IDEAL and correlate the quantitative magnetic resonance imaging (qMRI) results with clinical assessments of AS patients. METHOD: In total, 37 AS patients and 37 healthy controls were enrolled in the case control study. T2 mapping with and without fat saturation and IDEAL imaging were used to assess the multifidus (MF) and erector spinae (ES) at the levels of L3/L4 and L4/L5 for all subjects. Mean T2(non-fatsat), T2(fat), T2(fatsat), cross-sectional area (CSA), and fat fraction (FF) were compared between AS and healthy controls. Correlations of qMRI results with clinical assessments were analyzed in AS. RESULTS: Significantly elevated mean T2(non-fatsat) values and the FF of the MF and ES at both levels were observed in AS and compared to the controls (p < 0.05). The mean T2(fatsat) values of ES and MF were significantly higher only at the level of L3/L4 in AS compared to healthy controls (p < 0.05). A loss of muscle CSA compatible with atrophy was present in MF and ES at both levels in AS compared to the controls (p < 0.05). Weak to moderate positive correlations were found between FF and age and disease duration in AS (r = 0.318–0.415, p < 0.05). However, such positive correlation was not observed between FF and disease duration after adjusting for age (p > 0.05). CONCLUSIONS: Our findings indicate that using a combination of IDEAL and T2 mapping may provide deeper insights into the pathophysiological degeneration of paraspinal muscles in AS. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12891-022-05570-9.