Discussion
UIP, emphysema, IPF, lung cancer, CPFE, interstitial lung abnormalities
LUNG CANCER, UIP, COMBINED PULMONARY FIBROSIS AND EMPHYSEMA, EMPHYSEMA
In this study, we found that interstitial lung abnormalities identified on CTLS exams were associated with increased mortality. Such association had been demonstrated in a number of other previous studies on ILA, and our study in the CTLS population is consistent with those previous reports. Despite finding a lower prevalence of ILA in the current study, the association of mortality (HR 3.87) was similar to that in the various cohorts investigated by Putman et al. [5] where the risk of mortality ranged from HR 1.3–2.7.Our study demonstrated two additional key findings. First and most importantly, there remains a significant delay to diagnosis of ILD including progressive fibrotic ILD or IPF. Though most subjects with ILA in this cohort were referred to a pulmonologist after their baseline CT, the time to referral was on the order of years and the majority of patients were not referred for ILA but rather lung nodules. Similarly, in the quarter of individuals with ILA who were subsequently diagnosed with ILD during the study period, the mean time to diagnosis was nearly five years with earliest time to diagnosis of 1.14 years. When we specifically reviewed subjects categorized as typical or probable UIP by CT, 5 of the 10 patients did not receive a clinical diagnosis of ILD during the study period. Of the remaining 5, the mean time to diagnosis was 4.7 years. This long diagnostic delay could have been due to a number of factors including delay in referral, delay in recognizing ILA as ILD, and lack of symptoms at time of initial pulmonology evaluation. A recent study from Denmark evaluated reasons for diagnostic delay in IPF patients. They reported a median delay of 2.1 years and found that the largest contributors were delayed referral to a pulmonologist and subsequently to an ILD center [Second, our study also demonstrated that almost half of individuals with ILA have progression on follow-up CT scans. Other studies also have shown significant rates of progression, varying from 20% in the NLST [The findings of significant diagnostic delays and high incidence of progression highlight the need and opportunity to develop a system to identify individuals with ILD and bring them to specialist care earlier. CTLS programs may provide an opportunity to accomplish that goal as the CTLS population are at higher risk of ILD given their history of heavy smoking and serial CTs allow early identification of a progressive phenotype. Additionally, given the high prevalence of emphysema in this population, there may be a higher risk of combined pulmonary fibrosis and emphysema (CPFE) and the potential for worse outcomes [This study has several limitations. Although it is a large cohort, it is a single-center study and our sample is not ethnically diverse, which reflects the patient population of our center. This lack of diversity may limit the generalizability of our study. Another limitation is that our analysis was limited to the in-network participants due to lack of follow-up data in the out-of-network cohort (~ 80% of participants) for some primary outcomes (hospitalizations, pulmonary referral) and covariates. Our hospitalization data was also limited to in-network hospitalizations, so hospitalizations outside our network were likely missed. This most likely resulted in an underestimation of the true hospitalization rates. Further, the percentage of participants with ILA in our study was small which may have limited our ability to determine some significant associations (e.g., risk of lung cancer and hospitalization). There may be several reasons for the lower prevalence of ILA in our study compared to other CT lung screening cohorts. In the study by Jin, et al., ILA prevalence was nearly 10% [