Cryptogenic Organizing Pneumonia Is Associated With Increased Mortality Risk in Hospitalizations for Systemic Lupus Erythematosus (SLE): A National Inpatient Sample Analysis

Background This study analyzed the incidence, characteristics, and mortality risk associated with cryptogenic organizing pneumonia (COP) among hospitalizations for systemic lupus erythematosus (SLE) with lung involvement. Methods Adult hospitalizations from the 2016-2020 nationwide inpatient sample were analyzed using relevant International Classification of Diseases (ICD)-10 codes for SLE with lung involvement (M32.13) and COP (J84.116). We compared baseline characteristics of individuals with SLE and COP to those of other lung involvements using Chi-square tests for categorical variables and the Wilcoxon rank sum test for continuous variables. A Cox proportional hazards model was used to assess the risk of developing COP in the pooled cohort of SLE patients. The impact of COP on SLE mortality was assessed using multivariate logistic regression adjusting for illness severity, baseline risk of mortality at admission, and patient- and hospital-level covariates. Results Of 40,356 admissions for SLE, 3,175 (7.9%) were due to lung involvement, with COP identified in 570 cases (17.9%). Compared with other lung involvement in SLE, individuals with COP were significantly older (mean age: 65 vs. 44.3 years; p<0.001), mostly female (515; 90.4% vs. 2,305 males; 88.5%; p=0.572), had a greater baseline risk of mortality [diagnosis-related groups (DRG) major or extreme likelihood of dying: 360; 63.1% vs. 1,133; 43.5%; p<0.001], and had a higher prevalence of peripheral vascular disease (25; 4.4% vs. 39; 1.5%; p<0.001), and lower prevalence of lymphocytopenia (45; 7.9% vs. 359; 13.8%; p=0.001), and hypothyroidism (44; 7.8% vs. 357; 13.7%; p=0.001). Predictors of COP included female sex [adjusted hazard ratio (AHR): 1.46; 95% confidence interval (CI): 1.12-2.96; p=0.022]; hospitalizations occurring in the third quarter of the year (AHR: 1.37; 95% CI: 1.05-2.23; p=0.038); hospital stays of six days or longer (AHR: 1.71; 95% CI: 1.06-2.77; p=0.029); undergoing five or more procedures during the same hospitalization (AHR: 1.56; 95% CI: 1.26-3.56; p=0.041); coexisting lymphocytopenia (AHR: 1.92; 95% CI: 1.16-3.19; p=0.011); need for mechanical ventilation (AHR: 1.60; 95% CI: 1.48-3.93; p=0.049), presence of another autoimmune disorder (AHR: 1.37; 95% CI: 1.15-4.29; p=0.040), and being hospitalized at private, investor-owned hospitals (AHR: 2.62; 95% CI: 1.03-6.64; p=0.043). Mortality in SLE with lung involvement was correlated with age ≥ 60 years [hazard ratio (HR) (95% CI) 1.16 (1.05-1.56); p=0.012], coexisting lupus nephritis [HR (95% CI), 2.44 (2.04-3.49); p=0.031], cancer [HR (95% CI), 3.49 (2.19-5.79); p<0.001], liver disease [HR (95% CI), 9.82 (4.79-12.57); p<0.001]; immune deficiency [HR (95% CI), 2.22 (2.02-3.11); p=0.031], hypothyroidism [HR (95% CI), 4.67 (1.47-7.75); p=0.009], and high blood pressure [HR (95% CI), 3.15 (2.83-4.51); p<0.001]. In the multivariable analysis, COP remained significantly associated with an increased risk of mortality [AHR (95% CI), 1.43 (1.16-2.74); p=0.031]. The incidence of COP did not significantly impact hospitalization costs ($US 94,772 ± 14,759 vs. 95,982 ± 32,625; p=0.954) or length of stay (mean length of hospital stay: 8.3 vs.6.8 days; p=0.147). Conclusion Cryptogenic organizing pneumonia was associated with 1% of all hospitalizations for SLE and 18% of cases involving lung complications in SLE. The presence of COP significantly increased the risk of mortality in SLE patients with lung involvement.