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Juvenile idiopathic inflammatory myopathy: exercise-induced changes in muscle at short inversion time
R M Summers1, A M Brune, P L Choyke
1Dept. of Diagnostic Radiology, U.S. Food and Drug Administration, National Institutes of Health, Bethesda, MD 20892-1182, USA.
Purpose:
To study the effect of exercise on short inversion time inversion-recovery (STIR) magnetic resonance (MR) images of thigh muscles in children with juvenile idiopathic inflammatory myopathy.
Materials And Methods:
Thirty-two MR studies were performed in 19 patients with juvenile idiopathic inflammatory myopathy who performed stair-stepping exercise for up to 10 minutes (mean, 5.7 minutes). Baseline T1-weighted (n = 32) and STIR (n = 32) images and STIR images immediately (n = 32) and at 30 (n = 24) and 60 (n = 29) minutes after exercise were obtained at 0.5 T. Four radiologists graded STIR signal intensity changes, in observer performance experiments in which they were blinded to the order of image acquisition in relation to exercise.
Results:
Changes in muscle signal intensity were observed on STIR images obtained immediately after exercise in 20 of 32 (63%) studies. The mean signal intensity score immediately after exercise (1.7 +/- 1.0 [SD]) increased compared with the mean baseline score (1.4 +/- 1.1) (P = .0005) and resolved by 30 minutes after exercise. The magnitude of exercise-induced changes correlated with the amount of work performed (r = 0.51, P = .003) but not with disease activity or baseline signal intensity when the changes were corrected for work (r < 0.17, P > .35). Radiologists demonstrated moderate to substantial agreement in the grading of signal intensity changes after exercise (kappa = 0.60-0.84).
Conclusion:
In patients with juvenile idiopathic inflammatory myopathy, stair-stepping exercise induces signal intensity changes on STIR MR studies of muscle for approximately 30 minutes after exercise, in a distribution that may mimic active muscle inflammation.
Insights
Exercise causes temporary changes in thigh muscle MRI scans for children with juvenile idiopathic inflammatory myopathy. These signal intensity changes on short inversion time inversion-recovery (STIR) images resolve within 30 minutes post-exercise.
Area of Science:
- Pediatric Rheumatology
- Musculoskeletal Imaging
- Medical Imaging Techniques
Background:
- Juvenile idiopathic inflammatory myopathy (JIIM) is a condition causing muscle inflammation in children.
- Magnetic Resonance Imaging (MRI) is crucial for diagnosing and monitoring JIIM.
- Short inversion time inversion-recovery (STIR) sequences are sensitive to edema, a marker of inflammation.
Purpose of the Study:
- To investigate the impact of physical exercise on STIR MRI findings in the thigh muscles of children with JIIM.
- To determine if exercise-induced changes can be differentiated from active muscle inflammation on STIR MRI.
Main Methods:
- Thirty-two STIR MRI studies were conducted on 19 pediatric patients with JIIM.
- Patients performed stair-stepping exercise, with MR images acquired at baseline and at intervals post-exercise.
- Four radiologists assessed STIR signal intensity changes in a blinded observer performance study.
Main Results:
- Exercise induced significant STIR signal intensity increases in thigh muscles in 63% of studies immediately post-exercise.
- These exercise-related changes correlated with the amount of work performed.
- Signal intensity changes resolved by 30 minutes after exercise and did not correlate with disease activity.
Conclusions:
- Stair-stepping exercise can cause transient STIR MRI signal intensity changes in the thigh muscles of children with JIIM.
- These post-exercise findings may mimic active muscle inflammation, potentially complicating MRI interpretation.
- Understanding these exercise-induced changes is important for accurate diagnosis in JIIM patients.
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