Background Juvenile dermatomyositis (JDM) is a rare autoimmune disease in childhood and the only available diagnostic criteria currently used are those defined by Bohan and Peter in 1975 1-3. Potential pitfalls occur in the laboratory diagnosis of JDM because serum levels of muscle enzymes are not elevated in every case, electromyography (EMG)presents with sampling errors and even muscle biopsy specimens may be normal due to patchy muscle involvement. Changes in clinical practice have resulted in the use of non-invasive techniques, such as magnetic resonance (MR) imaging, in place of EMG and muscle biopsy in the diagnosis of JDM 4-6.
Objectives 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 tests, laboratorial exams, nailfold capillaroscopy and muscle biopsy.
Methods Twenty-three patients aged 6-19 years, 17 girls and 6 boys with a diagnostic of JDM were prospectively evaluated at any point during their illness course. All patients were evaluated 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 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 three (13%) patients. Muscle biopsy confirmed inflammatory myositis in these three patients. All three patients had elevation of at least one muscle enzyme and the nailfold capillaroscopy showed scleroderma (SD) pattern. CMAS was <52 in all three patients; MMT was <80 and DAS <20 in two patients (not done in one patient). Twenty patients had inactive disease. Nailfold capillaroscopy was normal in twelve patients and with SD pattern in six patients (not done in two patients). Muscle strength tests (CMAS and MMT) were normal in twelve out of twenty patients (MMT not done in four patients).
Conclusions Whole-body MR allows us to evaluate the extent and symmetry of muscle disease in a single exam by revealing muscles groups not seen with standard protocols. Muscle strength tests do not evaluate the accumulated effects in muscles over time in patients with JDM.
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Disclosure of Interest None Declared
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