Semi-quantitative thigh magnetic resonance imaging scores in assessing disease activity and determining long-term clinical outcome in idiopathic inflammatory myopathies: a causal mediation analysis
Authors' conclusion
Baseline fatty infiltration and muscle atrophy resulting from older age, female sex, longer disease duration and absent anti-synthetase antibodies, partly mediate muscle recovery in IIM.
Study context
- Population
- In inflammatory myositis (IIM) patients with semi-quantitatively scored thigh MRI (muscle oedema, fascial oedema, muscle atrophy, fatty infiltration)38 with follow-up
- Participants
- 59 patients
- Outcome
- Follow-up MMT-8 (dependent variable), with t-MRI scores as mediators of age, sex, symptom duration, autoantibodies, diabetes and BMI
Methodological detailssingle-centre, causal mediation analysis, Spearman correlation
- Single-centre
- Causal mediation analysis
- Spearman correlation
Main finding
As reported in the abstract
Total effects on follow-up MMT-8 via baseline t-MRI scores (estimate (95%CI)) · Median follow-up 31 (10-57) months
- Male sex, via atrophy
- 2.93 (0.44, 4.89)
- Male sex, via fatty infiltration
- 2.08 (0.54, 3.71)
- Antisynthetase antibody, via fatty infiltration
- 4.50 (0.37, 7.59)
- Age, via atrophy
- −0.09 (0.19, −0.01)
- Age, via fatty infiltration
- −0.07 (−0.15, −0.01)
- Disease duration, via fatty infiltration
- −0.18 (−0.27, −0.02)
Observational data: associations, not effects.
Further findings
Correlation of baseline MMT-8 with thigh MRI (t-MRI) scores (Spearman)
- Muscle oedema
- r = −0755
- Fascial oedema
- r = −0.443
- Muscle atrophy
- r = −0.343
Correlation of muscle enzymes with muscle oedema (Spearman) · baseline
- Creatinine kinase
- r = 0.422
- Aspartate transaminase
- r = 0.480
Correlation of follow-up MMT-8 with baseline t-MRI scores (Spearman) · median follow-up
- Baseline atrophy
- r = −0.497
- Baseline fatty infiltration
- r = −0.531
Original publication
Semi-quantitative thigh magnetic resonance imaging scores in assessing disease activity and determining long-term clinical outcome in idiopathic inflammatory myopathies: a causal mediation analysis. Rheumatology (Oxford). Published 20 April 2023. doi:10.
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