Outcomes and prognostic factors in Juvenile Dermatomyositis

Abstract

Background: Juvenile Dermatomyositis is a rare, presumably autoimmune disease of childhood, with an annual incidence of 1.9-3.2 per million children. Lately, validated measures for disease activity and damage in myositis have been developed, but scarce data about long-term outcome is available. Objectives: To investigate outcomes and predictors for outcomes in a Norwegian inception cohort of Juvenile Dermatomyositis patients, and to see how measures for muscular, pulmonary and health outcomes in JDM patients differ from that of matched controls from the general population. Methods: Patients with probable or definite JDM according to the Bohan-Peter criteria, diagnosis after 1970, disease onset < 18 years of age and disease duration > 2 years were identified from Norwegian hospital registries. The patients were clinically examined median 16.8 years (range 2.0-38.1) after symptom onset and were compared with age- and sex-matched controls (randomly selected from the Norwegian population register). Muscle strength was measured by the Manual Muscle Test (MMT) and Child Myositis Assessment Scale (CMAS); physical health by SF-36 PCS and pulmonary function by spirometry, body plethysmography and diffusion capacity for CO (DLCO). In patients, high resolution computed tomography (HRCT) and magnetic resonance imaging (MRI) of thigh muscles were carried out, and disease activity and damage was measured by Disease Activity Score (DAS), Myositis Damage Index (MDI) and Health Assessment Questionnaire (HAQ/child-HAQ). Early disease characteristics were assessed by chart review. Results: Sixty seven JDM patients were identified, which correspond to an average annual incidence of at least 1.8/million children in Norway from 1970-2005. 4 patients had died (6%); the remaining 63 could all be tracked, and 60 (95%) of those participated in the study (60% female). In patients, cumulative organ damage was found in 90% (included calcinosis in 47%), and physical disability in 40% (HAQ/child-HAQ>0). Muscle strength and physical function was lower in patients than controls (P`s < 0.001 and 0.014, respectively). Muscle weakness was found in 31% (CMAS) and 42% (MMT), but the impairment was mostly mild. MRI detected muscular damage was found in 52% (included muscular atrophy, calcinosis and fatty infiltration), and correlated with CMAS and MDI (P`s < 0.01). Patients had smaller lung volumes than controls (P=0.011). In patients, restrictive ventilatory defects and reduced diffusion capacity were found in 26% and 49%, respectively. HRCT abnormalities were found in 37%, and included interstitial lung disease (14%), calcinosis in the chest wall (14%) and airways disease (15%). High disease activity and damage 6 and 12 months post-diagnosis, predicted cumulative organ damage, calcinosis, muscle weakness and MRI detected muscle damage at follow-up. Conclusions: After median 16.8 years disease duration, a substantial portion of our JDM patients had cumulative organ damage, mild physical disability and unfavorable muscular outcomes. Although mostly subclinical, pulmonary involvement was found in the majority of patients. Our findings show that JDM patients have impaired function many years after diagnosis and that sustained early disease activity and damage predict an unfavorable outcome; also our study highlights the systemic nature of the disease. Hopefully, JDM outcomes will improve with advances in treatment.