The clinical features of juvenile dermatomyositis: A single-centre inception cohort.

Introduction: Juvenile Dermatomyositis (JDM), a severe and rare autoimmune disease, is the most common idiopathic inflammatory myopathy in children. We describe the clinical features of a large single-centre cohort.

Methods: We studied an inception cohort (0-18 years old) referred for diagnosis to the JDM clinic at The Hospital for Sick Children (SickKids), between January 1989 and September 2017. Probable or definite diagnosis of JDM was done according to the 2017 ACR/EULAR Criteria. We excluded children who had treatment started at another hospital. The data were collected retrospectively from clinical charts and the SickKids JDM database.

Results: 172/230 (74.8%) patients were included. They were most often female (female:male = 1.8:1); the age at diagnosis was 8.5±4.3 years. There was a positive family history for autoimmune disease in 52%, mainly rheumatoid arthritis. No patient died. The most common signs at inception were muscle weakness (85.5%), nailfold capillary abnormalities (83.4%), Gottron papules (78.5%), heliotrope rash (66.3%), abnormal gait (55.8%), and malar/facial rash (54.7%). The prevalence of Gottron papules, heliotrope rash, facial/malar rash, nailfold capillary abnormalities, Raynaud phenomenon, dysphonia/dysphagia (a frequent cause of hospitalization), mouth ulcers, calcinosis, eye problems, joint involvement, acanthosis nigricans and lipodystrophy increased during follow-up. Muscle enzymes, namely CK, ALT, AST, were often normal or only slightly raised despite active muscle disease; conversely LD was often high. Anti-Nuclear Autoantibodies were positive in 49.7% of patients at diagnosis. The course of the disease was: 29.1% monocyclic, 5.3% polycyclic, 33.1% chronic. The course of 56 patients (32.5%) was not classifiable due to length of follow-up. Corticosteroids were used as treatment in almost all our patients and 30% required intravenous therapy due to the severity of the presentation; methotrexate was added in 64%, more often in recent years. Unresponsive patients were treated mostly with intravenous immunoglobulins (IVIG).

Conclusions: The information obtained from this relatively large number of patients adds to the growing knowledge base of this rare disease.

Trial Registration: SickKids Research Ethics Board approved the study.