Juvenile idiopathic arthritis (JIA) represents the most common chronic inflammatory musculoskeletal disease in children. It is characterised by the onset of inflammatory arthritis prior to the 16th birthday and can follow many patterns ranging from oligoarthritis to polyarthritis to the most severe subtype, systemic juvenile idiopathic arthritis (sJIA). 1 The disease course can be variable with many children achieving drug-free remission. It is estimated that at least 60% of children will require systemic drug therapy with methotrexate, primarily but not limited to those with polyarthritis and systemic arthritis, and of these at least 20% will go on to require additional treatment with a biologic. 2 Mortality rates in JIA are reported to be increased when compared with the general population, but likely vary by subtype and disease severity. 3–5 It is important, however, to understand the potential mortality risk of this disease to ensure that children with JIA are referred early to specialist care. To this end, we investigated the mortality rates of children with sJIA and non-sJIA requiring immunosuppressant treatment with methotrexate and/or biologic therapy. A total of 1556 patients with JIA (196 with sJIA) recruited at the point of starting methotrexate(n= 542) or biologics (n= 1014) in the British Society for Paediatric and Adolescent Rheumatology Etanercept Cohort Study (BSPAR-ETN) or the Biologics for Children with Rheumatic Disease study (BCRD) were included. Patients were followed until death or 31 November 2014, whichever came first. Deaths were identified through regular study follow-up and linkage to the National Death Register. Standardised mortality rates (SMRs) were calculated using population rates per 1000 of the population of England and Wales, taken from the Office of National Statistics website from 2001 to 2013 as a comparator. 6 Ten deaths were reported, five in patients with sJIA and five in non-systemic patients. Median age at death was 11years, six patients were girls, and three had received stem cell transplants. Causes of death were varied and included infection (five patients including one septicaemia post stem cell transplant for rheumatoid factor-positive JIA), other complications post stem cell transplant (two patients with sJIA), macrophage activation syndrome, asthma and an accidental overdose.

The overall mortality rate was 1.1 per 1000 person-years with an SMR of 2.8 (95% CI 1.4 to 5.2)(table 1). Patients with sJIA had a higher mortality rate at 3.9/1000 person-years compared with 0.6/1000 person-years in those with nonsystemic disease. The SMR was highest in