Background/Purpose : The course of juvenile dermatomyositis (JDM) has improved greatly over the last 70 years with early and aggressive use of corticosteroids, immunosuppressive medications, and biologics. Yet it remains difficult to detect disease flare-up because symptoms may be mild, signs of the rash and muscle weakness vary widely and are often equivocal, and laboratory tests, including muscle enzyme levels are often normal. Electromyography and muscle biopsy are invasive and not reliable so alternative tools are needed to detect disease flare-up and decide if further treatment is needed. The objective of this study is to determine the effectiveness of muscle Magnetic Resonance Imaging (MRI) in detecting JDM flare-up and affecting physician’s decision-making regarding treatment.

Methods: Approval was obtained from the Internal Review Board of Nationwide Children’s Hospital. Subjects were included if they met the modified Bohan and Peter dermatomyositis criteria and were seen between 1/2005 and 6/2015. The MRI was performed on both lower extremities without contrast with the following sequences: Axial T1, axial T2 fat saturation, axial and coronal inversion recovery, and axial diffusion weighted. The physician decision that a subject with JDM was in a flare-up was considered as the gold standard, using rash, muscle weakness by childhood myositis assessment scale, muscle enzymes, and myositis on MRI. We compared the MRI result with the physician’s decision of relapse or not and evaluated whether there was a concordance or discordance between the MRI findings and the subsequent treatment decision.

Results: Forty-five JDM children were identified, of which 32 were females. The median age at diagnosis was 5.8 years. Eighty percent had weakness at diagnosis, 100% typical rash, 73% typical nail fold capillary changes. At diagnosis, muscle enzymes were compatible with JDM generally (CK 52%, LDH 62%, aldolase 72%, AST 54% abnormal), EMG abnormal in 3/8, muscle biopsy typical of JDM in 10/11, and MRI abnormal demonstrating myositis in 31/40. Thirteen of the 45 subjects had a repeat MRI for a possible flare-up with differing indications: general proximal weakness in 4 subjects, hip, thigh or calf pain in 3 subjects, rash in 3 subjects, worsening nail fold changes in one subject, elevated enzymes in one subject, and to confirm remission in one subject. Three of 13 repeat MRI’s were abnormal, demonstrating myositis. There was moderate agreement between the flare-up MRI findings and the physician’s treatment decision (kappa=0.59); in each abnormal MRI case the physician decided to increase treatment (Bayes rule 100% agreement). When the MRI was negative for myositis in 10 patients, 7/10 physicians chose to continue same medications or to taper medications (70% agreement).

Conclusion: Our study suggests that MRI at a time of a JDM flare-up is useful, yielding a sensitivity of 50% and a specificity of 100% for flare-up using a physician’s assessment of disease flare-up as the gold standard. Using Bayes rule, when an MRI shows myositis, physicians tend to treat 100% of the time and when an MRI shows no myositis, physicians in this study continued the same medications or tapered medications 70% of the time.  

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-role-of-muscle-mri-in-detecting-a-flare-up-of-juvenile-dermatomyositis/