Objectives To describe the characteristics, outcome and predictive factors of juvenile mixed connective tissue disease (JMCTD) in a nationwide cohort of patients.

Methods We examined 55 patients with JMCTD after a mean disease duration of 16.2 years (SD 10.0). Patients were registered according to Kasukawa's criteria. Remission criteria were defined according to those for juvenile idiopathic arthritis, plus absence of cytopenia, myositis, progressive sclerodactyly, lung and oesophageal manifestations. Organ damage was assessed with the Systemic Lupus International Collaborating Clinics (SLICC)/American College of Rheumatology (ACR) Damage Index and the Juvenile Arthritis Damage Index (JADI). Medical records were reviewed for early predictors for outcome, which were assessed by multivariate logistic regression analyses.

Results Three patients developed systemic lupus erythematosus (SLE). Fifty-two patients had continuous JMCTD; the most common manifestations were: Raynaud (100%), arthritis (94%), puffy hands (77%) and pulmonary manifestations (58%). SLE-like, systemic sclerosis (SSc)-like and polymyositis (PM)-like findings were found in 98%, 77% and 48%, respectively. Over time, SLE-like and PM-like manifestations decreased, and SSc-like findings increased. At follow-up, 35 patients (67%) had active disease and 17 (33%) were in remission. In 34 patients (65%), SLICC or JADI≥1 assessments indicated organ damage. Active disease was associated with higher anti-ribonucleoprotein antibody titres at follow-up and positive rheumatoid factor (RF) at diagnosis and follow-up.

Conclusions Most patients with JMCTD had active disease and organ damage after a mean follow-up of 16.2 years. Active disease was associated with higher anti-ribonucleoprotein antibody levels and positive RF. The presence of RF at diagnosis predicted persistent disease activity.