Background/Purpose: Juvenile dermatomyositis (JDM) is a rare autoimmune disorder, but remains the most commonly chronic inflammatory myopathy among children. A redefinition of the diagnostic criteria is currently underway and is likely to lead to non-invasive exams such as magnetic resonance (MR) imaging, in place of electromyography and muscle biopsy in the diagnosis of the disease.  Our goal was to demonstrate the benefit of whole-body MR imaging as a diagnostic tool in the detection of muscle inflammatory activity in JDM and to correlate these findings with clinical evaluation including muscle strength, laboratorial exams, nailfold capillaroscopy and muscle biopsy.

Methods: Thirty-three patients aged 6-19 years (median age, 12.1 years), 22 girls with a diagnose of JDM according to Bohan & Peter criteria were evaluated at any point during their illness course using clinical examination, muscle enzymes determination, muscle strength tests such as Childhood Myositis Assessment Scale (CMAS) and Manual Muscle Testing (MMT), nailfold capillaroscopy and short tau inversion recovery (STIR) whole-body MR imaging. JDM activity was evaluated by Disease Activity Score (DAS). An open muscle biopsy was performed in deltoids or biceps braquialis if muscle disease activity was detected on MR exam.

Results: Whole-body scanning gave a complete assessment of all muscles groups and disease activity was detected in STIR MR imaging in four (12.1%) patients confirmed by muscle biopsy. All four patients had elevation of at least one muscle enzyme and the nailfold capillaroscopy showed scleroderma (SD) pattern in these patients. CMAS, MMT and DAS means were 25.7, 32.3 and 9 respectively in patients with altered MR, and 48.1, 77 and 2.35 respectively in patients whose MR were normal. Twenty-nine patients had inactive disease (24 with medication and five without medication). Nailfold capillaroscopy was normal in 16 patients and with SD pattern in nine patients (not done in four patients). Muscle strength tests (CMAS and MMT) were normal in 16 out of 29 patients (MMT not done in four patients). 

Conclusion: Whole-body MR allows us to evaluate the extent and symmetry of muscle disease and inflammatory activity in a single exam by revealing muscles groups not seen with standard protocols. Nailfold capillaroscopy is an important additional exam to assess disease activity. Muscle strength tests are important to evaluate not only the disease in the acute phase, but the accumulated effect over the same time.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/whole-body-magnetic-resonance-imaging-a-new-diagnostic-tool-in-the-assessment-of-activity-in-juvenile-dermatomyositis-patients/