Longitudinal assessment of disease activity and muscle strength in juvenile dermatomyositis: a multicentre registry study.

Objectives: To define disease activity measures, muscle strength and functional assessments in new-onset juvenile dermatomyositis (JDM) patients, at disease onset and follow up.

Methods: A registry was set up in 18 hospitals, enrolling patients over 3-years (2015-2018). Clinical assessments were performed at baseline, and at 6, 12, 18 and 24 months after diagnosis. Disease Activity Score (DAS20), skin and musculoskeletal DAS sub-scales; Manual Muscle Test (MMT8); Childhood Myositis Assessment Scale (CMAS); Childhood Health Assessment Questionnaire disability index (CHAQ_DI 0-3) and 10 cm Visual Analog Scale (VAS) for overall wellbeing scores were compared by Poisson Model and Wald post-test for repeated measures.

Results: Ninety-six cases, being 61 (64%) females, median age 10 years had JDM diagnosis and 12 (13%) onset calcinosis. Mean ±SD scores at diagnosis and 6 months intervals for DAS20 (0-20) were 7.8±5, 6.3 ±4.8, 5±4, 4.9 ±5 and 0.5 ±2.3; with significant difference from baseline (p<0.01). Skin DAS subscales were 2.8±3.3, 1.8±2.9, 1,1±2.2, 0.6±1.8, 0.4±1.5. MMT (0-80) 62.6±20.4, 70.2±13.5, 73.3±11, 75.7±7.9 and 74.8±7.8, with significant difference from baseline up to 6 months (p=0.016); CMAS (0-53) 29.5±11.4, 33.1±8.3, 34.2±5.8, 34±6 and 33.3±5.4. CHAQ-DI (0-3) 1±0.9, 0.6±0.7, 0.8±0.8, 1±0.8 and 1±0.3; parents VAS 4.1±2.5, 2±2.1; 1.3±2.8, 4.1±3.1, 1.7±2.2. There was no significant difference for CMAS, CHAQ-DI and parents VAS from baseline up to 24-month assessment.

Conclusions: DAS20 scores improved gradually during follow up, MMT8 improved significantly during the first 6 months and CMAS, CHAQ-DI and parents VAS scores had no significant improvement with persistent functional impairment over 2-years.