The objective was to estimate the incidence of lung disease among patients with systemic lupus erythematosus (SLE).
Using Swedish register data, we identified patients with SLE and pulmonary diagnoses from the National Patient Register through ICD codes. We matched patients with SLE with individuals from the general population. Patients with SLE with a history of pulmonary disease were excluded. Incidence rates (IR) and 95% confidence intervals (CI) were calculated overall and by type of pulmonary disease for incident (2003-2013) and prevalent SLE separately. Hazard ratios (HR) and 95% CI of the association between SLE and pulmonary disease were estimated using adjusted Cox regression models. Sensitivity analyses using a semi-automated approach to quantitative probabilistic bias analysis accounted for potential bias due to unmeasured confounding by smoking.
There were 3209 incident and 6908 prevalent cases of SLE identified. The IRs for pulmonary disease were similar in prevalent and incident SLE (∼14 cases per 1000 person-years). Patients with incident SLE had a nearly sixfold higher rate of pulmonary disease compared to the non-SLE population (HR 5.8 (95% CI 4.8-7.0)). Incident and prevalent SLE was associated with an increased rate of interstitial lung disease (HR 19.0 (95% CI 10.7-34.0) and 14.3 (95% CI 10.8-18.8), respectively). Bias due to unmeasured confounding by smoking was unlikely to explain our findings.
Lung disease is relatively common in patients with SLE compared to the general population. Clinicians caring for patients with SLE should have heightened suspicion of lung disease, including interstitial lung disease, even early within the disease course or at the time of diagnosis of SLE.