gms | German Medical Science

Introduction: Patients with inflammatory rheumatic diseases such as rheumatoid arthritis, ankylosing spondylitis or systemic lupus erythematosus can develop a secondary immunodeficiency (SID) due to drug therapy and/or suffer from an underlying primary immunodeficiency (PID). Although these patients show an increased susceptibility to severe infections, little is known about immunodeficiency prevalence in patients with underlying rheumatic diseases. This study describes the prevalence of PID in the German statutory health insurance (SHI) system and investigates SID diagnosis in patients with hematologic as well as autoimmune diseases including rheumatic patients.

Methods: The study used SHI claims data from Germany, including data from almost 4 million insured patients from 2013 to 2019. To estimate the prevalence of PID, we used ICD-10-GM codes proposed by [1], including patients with immunoglobulin replacement therapy, excluding patients with underlying diseases (cf. Table 1 [Tab. 1]). To investigate SID in rheumatic patients, we included patients with rheumatic disease diagnoses and screened for ICD-10-GM codes for immunodeficiency and severe infection occurrence.

Results: Extrapolated to the German SHI population, 6,116 patients suffered from PID in 2019, with prevalence slightly increasing between 2017 and 2019. SID prevalence was significantly higher: 10,839 patients were estimated to have SID and rheumatic disease in 2019. Of all investigated SID patients, a comparable amount have rheumatic diseases and underlying oncological diseases (42% vs 41.5%, respectively).

The proportion of SID diagnoses, however, was strikingly low: only 1,661 out of 121,414 patients with SID-relevant underlying diseases in our sample of 3,876,859 patients, had an immunodeficiency diagnosis. In contrast, 24,412 out of these 121,414 patients had at least one severe infection as inpatients, or three infections within four quarters as outpatients. Around 70% of all patients with severe infections were patients with rheumatic diseases (cf. Table 1 [Tab. 1]), which is significantly higher than the proportion of patients with both rheumatic disease and a concomitant diagnosis for immunodeficiency.

Conclusion: The study shows that in patients with rheumatic diseases, SID is generally more prevalent than PID. Many patients with rheumatic diseases suffer from severe infections but are not diagnosed with immunodeficiency. Our study provides a good starting point for future research in the link between rheumatic disease, SID and patient diagnostics and monitoring.

Disclosures: The study was funded by Takeda.