INTRODUCTION
Systemic juvenile idiopathic arthritis (sJIA), the least common subtype of juvenile idiopathic arthritis (JIA), is a chronic inflammatory disease characterized by fever, arthritis, and at least one of the following: rash, generalized lymphadenopathy, hepatomegaly/splenomegaly, and/or serositis 1. Compared to other subtypes of JIA, sJIA can cause more severe systemic complications including pericarditis and pleuritis. Pulmonary complications of sJIA such as pulmonary hypertension, interstitial lung disease, and pulmonary alveolar proteinosis are rare, but can cause significant morbidity and mortality2,3. Childhood interstitial lung disease (chILD) in general is a rare and heterogenous group with prevalence ranging from 0.8 - 2.1 per million in Australia and Asia to 3.6 cases per million in the United Kingdom and Ireland 4,5. Since the early 2010s, researchers identified an increased incidence of interstitial lung disease (sJIA-LD) in pediatric patients with sJIA, with a 2020 cohort estimating a new prevalence of almost 7% 6. This is a new development in the clinical presentation of sJIA, as prior to 2000, published literature on sJIA-LD were primarily case reports7. In 1980, Athreya et al reported a rough estimate of 4% of patients with juvenile rheumatoid arthritis had pleuropulmonary disease, but they did not describe percentage of lung disease in sJIA8. Given the high mortality rate of sJIA-LD6, researchers have attempted to identify the pathophysiology and underlying risk factors of sJIA-LD. Identified demographic risk factors include disease onset at less than 2 years of age and presence of trisomy 21 2,9. Common clinical features were minimal respiratory symptoms, lymphadenopathy, hepatosplenomegaly, and clubbing 6,10. Radiographic findings included septal thickening and ground glass opacities6,9.
Therapeutic management plans are complicated in children with sJIA-LD. Some studies have identified a correlation between increased use of anti-cytokine therapy for sJIA in the early 2010s and the increase in sJIA-LD 6, 9, 10. However, one confounding factor is that patients with sJIA-LD often have increased severity of systemic symptoms, which could require increased medication exposures. For instance, a history of macrophage activation syndrome (MAS), a life-threatening complication of rheumatic disease, appears to be a common finding in those with sJIA-LD, highlighting the severity of these patients’ disease 2, 6, 10. Despite the increase in prevalence of sJIA-LD, little is known about this disease process, and we seek to broaden the field of knowledge on this subject. In this single-center, retrospective case series of 9 patients, we analyzed demographic, clinical, radiographic, and laboratory data to corroborate common clinical characteristics and present our clinical guidelines for diagnosis and monitoring of interstitial lung disease in children with sJIA.