Epidemiological analysis of kidney involvement in systemic lupus erythematosus using the national database of designated intractable diseases of Japan: a cross-sectional study of renewal applicants.

OBJECTIVE

To estimate the prevalence of active kidney involvement and its associations with comorbidities and treatment patterns among patients with systemic lupus erythematosus (SLE) at renewal application for the Designated Intractable Diseases of Japan.

METHODS

We analyzed Medical Certificates of Designated Intractable Diseases that were submitted in 2016 for the renewal of SLE designation. Among 35,207 digitized patients (mean age, 51.1 ± 15.7 years), active kidney involvement was defined as proteinuria (≥ 0.5 g/day) and/or urinary casts (granular casts or red blood cell casts) recorded as Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) items during the 6 months preceding the renewal application.

RESULTS

Active kidney involvement was identified in 8273 patients (23.5%). Compared with those without active kidney involvement, patients with active kidney involvement had a younger mean age at disease onset (32.6 ± 15.3 vs. 34.1 ± 15.2 years) and a lower proportion of females (84.3% vs. 90.5%). They more frequently had comorbid infection (14.6% vs. 10.6%), diabetes mellitus (16.2% vs. 11.2%), and hypertension (43.6% vs. 25.6%), and had higher disease activity (mean SLEDAI, 14.8 ± 9.4 vs. 7.0 ± 6.4). Glucocorticoid use was more common (94.9% vs. 91.8%), fewer patients received ≤ 7.5 mg/day (45.9% vs. 59.2%), and concomitant immunosuppressant use was higher (60.8% vs. 44.1%).

CONCLUSION

Approximately one-quarter of Japanese patients with SLE undergoing renewal had active kidney involvement, which was associated with higher disease activity, more comorbidities (notably hypertension), and greater use of glucocorticoid and immunosuppressants.