Muscle MRI at the time of questionable disease flares in Juvenile Dermatomyositis (JDM).

BACKGROUND: The course of JDM has improved substantially over the last 70 years with early and aggressive treatments. Yet it remains difficult to detect disease flares as symptoms may be mild; signs of rash and muscle weakness vary widely and are often equivocal; laboratory tests of muscle enzyme levels are often normal; electromyography and muscle biopsy are invasive. Alternative tools are needed to help decide if more aggressive treatment is needed. Our objective is to determine the effectiveness of muscle Magnetic Resonance Imaging (MRI) in detecting JDM flares, and how an MRI affects physician's decision-making regarding treatment.

METHODS: This study was approved by the Institutional Review Board of Nationwide Children's Hospital. JDM patients were consulted between 1/2005 and 6/2015. MRIs were performed on both lower extremities without contrast sequentially: axial T1, axial T2 fat saturation, axial and coronal inversion recovery, and axial diffusion weighted. The physician decision that a JDM patient was in a flare was considered the gold standard. MRI results were compared with physician's decisions on whether a relapse had occurred, and if there was a concordance between the assessment methods.

RESULTS: Forty-five JDM patients were studied. Eighty percent had weakness at diagnosis, 100% typical rash, and 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 was abnormal in 3/8, muscle biopsy typical of JDM in 10/11, and MRI abnormal demonstrating myositis in 31/40. Thirteen patients had a repeat MRI for possible flares with differing indications. Three repeat MRI's were abnormal, demonstrating myositis. There was moderate agreement about flares between MRI findings and physician's treatment decisions (kappa = 0.59). In each abnormal MRI case the physician decided to increase treatment (100% probability for flares). MRI was negative for myositis in 10 patients, by which 7/10 the physicians chose to continue or to taper the medications (70% probability for non-flares).

CONCLUSION: A muscle MRI would facilitate objective assessments of JDM flares. When an MRI shows myositis, physicians tend to treat 100% of the time. When an MRI shows no myositis, physicians continued the same medications or tapered medications 70% of the time. Further studies would help confirm the utility and cost-effectiveness of MRI to determine JDM flares.