Muscle MRI as Complementary Diagnostic Tool for Juvenile Dermatomyositis

Muscle magnetic resonance imaging may complement a physician's objective assessment in juvenile dermatomyositis, although negative MRI findings should not preclude treatment continuation.

Muscle magnetic resonance imaging (MRI) may complement a physician’s objective assessment of juvenile dermatomyositis (JDM), although negative MRI findings should not preclude treatment continuation, according to a study recently published in Pediatric Rheumatology.1

A chronic and common inflammatory myopathy of autoimmune origin, JDM can affect multiple organs, including the skin, muscles, and lungs. The disease can effectively be treated with methotrexate as first-line medication, in order to avoid muscle weakness, an adverse effect of commonly prescribed prednisone.2

The significant morbidity associated with JDM — including interstitial lung disease,3 cardiac disease,4 and calcinosis5 — renders its early diagnosis all the more imperative.

An update to diagnostic criteria for JDM was developed based on responses to an international survey taken by members of the Network for JDM and the Paediatric Rheumatology International Trials Organisation. These criteria include: proximal muscle weakness and characteristic skin rash (100% of respondents) and elevated muscle enzymes (86.8%  of respondents).6 In addition, muscle biopsy and MRI, myopathic changes on electromyogram (EMG), as well as “myositis-specific or -related antibodies, nailfold capillaroscopy, factor VIII-related antigen, muscle ultrasound, calcinosis and neopterin” (35.3% of respondents) are considered for JDM diagnosis.6

Muscle weakness in patients may be due to JDM flare, a result of steroid treatment, or some other cause. In cases in which the underlying cause for muscle flares is unclear, muscle enzyme assays are conducted. As false negative results on these tests are not uncommon, muscle MRI represents an alternative method for investigating the cause of inflammation.7

In the current study, the researchers sought to determine whether MRI of lower extremity muscles could accurately detect disease flares in patients with equivocal clinical assessment and test results.

The records of 45 patients (median age, 5.8; 71.1% girls) with JDM who consulted at the Nationwide Children’s Hospital, Columbus, Ohio, between January 2005 and June 2015 were examined. Patients exhibited the following symptoms: JDM-characteristic rash (100%), muscle weakness (80%), and nail fold capillary changes (73%). Abnormal results were found on the following tests: skin biopsy (100%), muscle biopsy (90%), MRI (77%), aldolase (72%), lactate dehydrogenase (62%), aspartate aminotransferase (54%), creatine kinase (52%), and EMG (38%).

Muscle MRI was carried out at initial presentation as a diagnostic tool for JDM in 40 out of 45 patients; repeat MRI was conducted in 13 patients with equivocal flares, for whom prior history, clinical examination, and muscle enzyme tests were obtained. Decision to repeat a muscle MRI was based on: weakness (n=4), rash (n=3), high levels of muscle enzyme (n=1), nail fold capillary dilation in the absence of flares (n=1), hip pain (n=1), thigh pain (n=1), calf pain (n=1), and remission assessment (n=1).

Two patients had a third MRI to assess whether they were in remission, prompting treatment discontinuation: 1 had a normal MRI, treatment was tapered, and the patient continued without any further flares; the other patient showed “bright T2 signal within the patellar tendons and superficial fasciae bilaterally,” suggesting active myositis, and the patient’s treatment was continued.

“Overall, there was moderate agreement between the second MRI findings and physician’s decision about flares (κ = 0.519). However, based on conditional probability of treatment given MRI findings, the agreement is revealed to be more substantial. When the MRI findings show myositis, physicians tend to treat for myositis 100% of the time, while when MRI findings show no myositis, physicians tapered treatment 70% of the time,” the researchers noted.

No significant association was found between abnormal MRI findings and elevated muscle enzymes (McNemar’s test p-value = 1.0000).

The researchers concluded that “[This] study suggested that a muscle MRI might be valuable as a test to inform a physician’s decision about whether a child with JDM is having a disease flare when other findings or tests may not be helpful.”

Limitations and Disclosures

  • This was a retrospective study
  • The sample size was small (n=45)
  • Flares were subjectively assessed by physicians
  • The cost-effectiveness of MRI was not evaluated

Two of the authors were supported by a grant from the CureJM Foundation.


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