Disease frequency, patient characteristics, comorbidity outcomes and immunosuppressive therapy in systemic sclerosis and systemic sclerosis-associated interstitial lung disease: a US cohort study

OBJECTIVES: To investigate prevalence estimates and incidence rates (IRs) for SSc and SSc-associated interstitial lung disease (SSc-ILD) cohorts and describe patient characteristics, immunosuppressive therapy (IST) and comorbid outcomes among incident SSc and SSc-ILD cohorts. METHODS: Data were obtained from the US IBM MarketScan (2008–2017) claims database using algorithms developed with expert consultation. For the SSc cohort, newly diagnosed patients (aged ≥18 years) had one or more diagnostic claim for SSc. For the SSc-ILD cohort, patients had an additional ILD claim. Sensitivity analyses using two or more claims or alternative ILD diagnostic codes were also conducted. RESULTS: When requiring one or more diagnostic claim, the prevalence of SSc and SSc-ILD per 100 000 persons was 72.1 and 19.0. The IR for SSc and SSc-ILD per 100 000 person-years was 18.3 and 4.3. Sensitivity analyses requiring two or more claims yielded much lower prevalence (SSc: 41.5; SSc-ILD: 13.3) and IR (SSc: 8.8; SSc-ILD: 1.6) estimates. Patients with SSc-ILD were older, with increased comorbidities and diagnostic procedures at baseline. MTX and MMF were the most common ISTs; 12.7% of the SSc-ILD cohort received therapy at baseline vs 8.2% for SSc. A total of 42.5% and 45.0% of the SSc and SSc-ILD cohorts, respectively, started a stable IST regimen and 21.7% and 19.4% of these had an escalation. Skin disorders were the most common comorbid outcome in both cohorts during follow-up. CONCLUSIONS: SSc, with or without associated ILD, is a rare disease in the US. Newly diagnosed patients with SSc-ILD had received more IST and had more comorbidities compared with newly diagnosed SSc.