Background: Patients with an existing immune mediated inflammatory disease (IMID) may be more likely to develop other IMIDs based on limited research. We sought to compare the risk of developing subsequent IMIDs among patients with and without an existing IMID.
Methods: IMID risk was estimated in a large US insurance claims database (MarketScan Commercial Claims and Encounters, 1/2006–9/2015) for patients with each of 9 initial IMIDs (ankylosing spondylitis [AS], celiac disease [CE], hidradenitis suppurativa [HS], inflammatory bowel disease [IBD]; lupus [LU], psoriatic arthritis [PsA], psoriasis [PsO], rheumatoid arthritis [RA], uveitis [UV]). Up to 1,000 controls were matched with replacement by age, sex, state of residence and insurance type to case patients aged 18–64 who had an initial, incident IMID. Initial IMIDs were identified with ICD-9 diagnosis codes on ≥2 medical service claims ≥30 days apart. A case patient's earliest IMID claim was designated as the index date for the case and all matched controls. The 8 secondary IMIDs were identified by their first claim after the index date. All subjects had to have ≥365 days of continuous health plan enrollment before and after their index date. Risk of developing a secondary IMID (each of 8 and any of the 8) was analyzed by initial IMID with stratified Cox proportional hazards models and clustered standard errors to account for case-control match group.
Results: Among 398,935 cases, mean age was 46 years and 63% were female. Mean number of matched controls per case was 644. Across the 9 initial IMID cohorts, range of median follow-up was 918–1,023 days for cases and 883–971 days for controls. Overall, any secondary IMID occurrence was significantly higher for cases (range: 5.2–47.2%) than for controls (range: 0.8–1.1%). Relative to matched controls, patients with an initial IMID had significantly higher risk of developing any of the other 8 secondary IMIDs (p≤0.002) (Table 1).
Patients with IBD as the primary condition had 7.5 times higher risk of developing a subsequent IMID compared with controls.
Conclusions: The incidence risk for developing a subsequent IMID was significantly higher for patients newly diagnosed with an initial IMID than matched controls without the same initial IMID. Considering the risk of developing a subsequent immune-mediated comorbidity while establishing treatment goals may help maximize patients' long-term health-related quality-of-life.