Co-morbidity and mortality among patients with interstitial lung diseases: A population-based study

Co-morbidities are frequent among patients with interstitial lung diseases (ILD). The objective of this study was to investigate their impact on mortality.

We used the Danish National Patient Registry (DNPR) to identify all patients with a first-time diagnosis of ILD between 1998 and 2010. Patients with ILD were matched 1:4 with controls from the background population. The burden of co-morbidity was assessed using the Deyo-Charlson co-morbidity score (DCcs). Mortality risks were assessed using Kaplan-Meier survival curves, and hazard rate ratios (HRR) for death were estimated using Cox proportional hazards regression models.

We identified 10 629 patients with ILD with a corresponding incidence estimate of ILD in Denmark of 17.6 per 100 000 inhabitants (95% CI: 16.5-18.7). Mean age was 72 years and 45.6% of the patients were females. Co-morbidity (DCcs ≥ 1) was present in 30% of the ILD patients and 12% of the controls (P < 0.001). The 5-year survival was 56.0% (95% CI: 54.6-56.6) among ILD patients and 84.0% (95% CI: 83.7-84.4) among controls. HRR for death among patients with ILD was 3.82 for males (95% CI: 3.63-4.02) and 3.85 for females (95% CI: 3.62-4.09) with matched controls as reference. Decreasing survival was seen with increasing DCcs for both groups. The 5-year survival for DCcs = 0 was 61% for ILD and 87% for controls compared with 41% versus 58% for DCcs = 2.

Survival was impaired for patients with ILD for all levels of the DCcs, although increasing burden of co-morbidity tended to close the mortality gap.