OBJECTIVES: We compared comorbidities and healthcare cost and resource utilization (HCRU) in patients with juvenile idiopathic inflammatory myopathy (JIIM) and juvenile idiopathic arthritis (JIA) in the US.

METHODS: Deidentified patient claims data from children (2-17 years) with JIIM or JIA diagnosed between Jan 01, 2018-Dec 31, 2021 (first date of diagnosis [index]) were retrieved from IQVIA PharMetrics^® Plus, a US healthcare insurance medical claims database. Patients (≥2 claims) in any setting and continuous enrollment in healthcare insurance plans (≥12-months pre-and post-index) were included. Patients diagnosed with both JIIM and JIA were excluded. Baseline covariate adjustment through propensity scores and stabilized inverse probability treatment weighting was performed. Comorbidities, total costs, and pharmacy burden were assessed 12-months post-index (JIIM=105;JIA=1841). Standardized mean differences (SMD)≥0.1 were considered noteworthy.

RESULTS: Post-index comorbidities were reported more frequently in patients with JIIM vs JIA: Sjogren's syndrome (2.2% vs 0.3%; SMD:0.17), dysphagia (7.9% vs 0.9%;SMD:0.34), dysphonia (2% vs 0.4%;SMD:0.15), interstitial lung diseases (3.2% vs 0.2%;SMD:0.24), and other juvenile comorbidities (7.7% vs 4.8%;SMD:0.12). Total (medical+pharmacy) encounters (47 vs 28;SMD:0.59) and costs (Total:$21,245 vs $11,643;SMD:0.44; medical:$15,212 vs $4612;SMD: 0.43; pharmacy:$3975 vs $2198;SMD:0.31) were higher for patients with JIIM vs JIA. In patients with JIIM vs JIA: (i) for corticosteroids, more encounters (8 vs 2;SMD:1.05), higher utilization (69.5% vs 41.8%;SMD:0.58), higher costs ($300 vs $23;SMD:0.77), and more days on corticosteroids (180 vs 14;SMD:1.24) (ii) for immunomodulators, more encounters (11 vs 7;SMD:0.93), higher utilization (64% vs 46.2%;SMD:0.36), and higher costs ($378 vs $142;SMD:0.44) (iii) for intravenous immunoglobulin (IVIG), more encounters (10 vs 7;SMD:0.30), higher utilization (40.6% vs 0.4%;SMD:1.15), and higher costs ($67,512 vs $35,156;SMD:1.15) were reported.

CONCLUSIONS: Comorbidities, HCRU, and treatment utilization evidenced by a disproportionate use of corticosteroids, immunomodulators, and IVIG were higher in patients with JIIM vs JIA. IVIG utilization, a big driver of cost, was~100-fold higher in JIIM vs JIA.