Objective: Large, population-based assessments of systemic sclerosis (SSc) prevalence and comorbidity in the United States (US) are rare. We explored autoimmune disease and other comorbidity patterns among SSc patients in the US from 2001 to 2002 and compared these with controls.
Research design and methods: Two US datasets with patient-level medical and drug claims were used to assess SSc prevalence and comorbidity: IMS Health Integrated Administrative Claims Database (IMS Health) and the MarketScan Commercial Claims and Encounters Database (MarketScan). SSc patients and comorbidities were identified by International Classification of Diseases (ICD), 9th revision diagnostic codes appearing on medical claims. Patients without SSc diagnostic codes (controls) were selected and matched 4:1 to SSc patients based on sex, age, Census Bureau region, and previous insurance coverage. The prevalence relative risk (RR) statistic compared comorbidity occurrence between SSc patients and controls, with 95% confidence intervals estimated using the Mantel-Haenszel method. Several sensitivity analyses tested methods used for identifying SSc cases and the prevalence of comorbidities.
Results: In both databases, SSc prevalence was 0.05% using the standard population model, 0.03% under sensitivity analysis. Among SSc patients the risks for inflammatory bowel disease (IBD) and multiple sclerosis (MS) were notably higher across datasets than for those without SSc: RR 3.2-6.6 for MS, RR 2.1-2.2 for IBD, in MarketScan and IMS Health, respectively (p < 0.05 for all). The chronic disease burden of SSc patients was much higher than that of controls, as confirmed by two chronicity measures (Chronic Disease Score, Elixhauser Comorbidity Index). The risks for cardiovascular, renal, liver and several neuropsychiatric diseases were higher for SSc patients across both datasets. Sensitivity analyses supported these findings.
Conclusions: These data provide a population-based estimate of US prevalence of SSc and document the higher risk for certain other autoimmune diseases among SSc patients when compared to controls. Patients with SSc also had a higher chronic disease burden than those without SSc. These findings are limited by the unknown validity of ICD-9 codes for SSc case identification, unbalanced regional representation, and a likely 'healthy worker' effect in these databases.