Background/Purpose:   Few studies describe the natural course and long term outcomes of myositis in childhood in large, prospectively-followed patient cohorts, treated in the modern era. We aimed to describe long term patient-reported outcomes in adolescents and young adults (≥ 16 y) who had myositis in childhood and to find outcome predictors from data in the Juvenile Dermatomyositis Cohort and Biomarker Study, UK and Ireland (JDCBS)

Methods: Participants in the JDCBS, previously diagnosed with idiopathic inflammatory myopathy and now aged 16 years or over, completed the SF36 v2, HAQ and a newly developed questionnaire to collect information on current disease features and damage, medication use and side effects, and education and employment opportunities.  

Results: Of 205 sets of questionnaires sent, 84 (41%) were returned. Average age of respondents was 21.5 years (maximum 30.8y). Average disease duration was 11.8 y (SD 5.1), age at onset 9.2y (SD 4.3) and female to male ratio 4.25:1. Most patients were white (82.1%) and had a diagnosis of Definite Juvenile Dermatomyositis (69%). Of the 68 who had Myositis-Specific Autoantibody testing, eight (11.8%) had TIF1γ and eight had NXP2. Six (8.8%) were positive for Mi2. Nine (13.2%) had unknown bands and 14 (20.6%) were negative. Of note, 49 (59%) reported persistently active disease and 54 (65%) were still taking immunosuppressive medication for myositis. Among respondents at school or in higher education, 13 out of 29 (44.8%) reported that their academic results were adversely affected by myositis, and that time missed, muscle weakness and fatigue were all significant contributors. Around two-thirds of respondents found that myositis had made it difficult to study. Fourteen of 50 (28%) reported career compromise caused by myositis; of these, 10/37 (27%) were employed and 4/13 (30.8%) were unemployed. Among 47 patients aged 18 to 24 there were 21 (44.7%) who were employed; patients in this study were twice as likely to be unemployed compared to the corresponding age group in the UK population (p=0.001, OR 0.456, 95% CI 0.24, 0.84). SF36 Physical Composite Scores (PCS) were significantly better in those who did not report current myositis (p=0.0003) arthritis (p=0.002) or muscle weakness (p=0.0001). Mental Composite Scores (MCS) were also better in those who did not report current arthritis (p=0.03) or muscle weakness (p=0.013). Intensity indices were calculated for skin DAS, CMAS and MMT by dividing area under the curve (AUC) of score trajectories by the duration (y) of study follow-up. There was significant correlation between MCS and MMT index scores (p=0.007, rho 0.328). This association remained significant after fitting a quantile regression model to predict changes in the median MMT intensity score as a function of MCS after adjusting for education/employment status.  

Conclusion: We found high patient-reported rates of persistently active disease and medication use in long term follow-up of juvenile myositis, although response bias exists. The young people had reduced rates of employment compared to the UK general population. Persistent muscle disease affected quality of life outcomes in this cohort.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/juvenile-dermatomyositis-what-comes-next/