Subjects undergoing LT for OLD manifested a 2-fold increased mortality risk in the first post-transplantation year. This risk was limited to the stratum of non-silicotics and attenuated after the first year post-LT. Importantly, our observations differ from an earlier single-centre report of poorer post-LT survival in silicotics compared with idiopathic pulmonary fibrosis, an analysis that did not adjust for covariates accounted for in our analysis [7
By using US national data, employing a reasonable strategy to select registry-based referents consistent with prior lung transplant analyses, and controlling for multiple cofactors [9
], we were able to unmask a previously unidentified pattern of poorer survival following LT for OLD. Our findings provide epidemiological context to prior case reports (including one of the first reported human lung transplants with extended post-surgical survival) and two single-centre analyses of LT performed for OLD [2
Even in such a large cohort of LT recipients, transplantation for OLD is relatively rare. We cannot exclude, however, that other cases of OLD might have been obscured within the OPTN-R diagnostic coding schema. For example, a separate code allows for hypersensitivity pneumonitis without allowance for a specific cause. Also, the OPTN-R does not capture potentially relevant recipient characteristics and has limited information on cause of post-transplant death. Indeed, cause of death was missing for 38% of non-silicotic OLD cases. These limitations make it challenging to identify causal mechanisms for the observed pattern of risk. Potential explanations may be that non-silicotic OLD cases had concurrent co-morbidities such as secondary pulmonary hypertension or were exposed to empiric immunosuppressive therapy prior to LT, thereby increasing the risk for infectious complications post-transplant. Nevertheless, while the excess early mortality risk appears to be contributed by non-silicosis OLD, assigning a cause for this, as well as the later convergence in mortality risk among the three groups, would be highly speculative. Lastly, the non-silicotic OLD group was heterogeneous. Thus, it is not possible using an epidemiological approach to isolate individual characteristics that might have accounted for the observed grouped differences in mortality risk. It is unlikely, although not impossible, that unmeasured confounding played a role. If it did, it would have had to operate uniformly across this very same heterogeneity. Given the myriad of factors that impact individual post-transplant survival, including post-operative technical and infectious complications, it is unlikely that other approaches to referent selection or stratified sub-analyses would better control for such confounders, if indeed they were present.
In sum, practitioners should be cognizant that persons with end-stage non-silicosis OLD may have an increased mortality risk in the first year after LT. There is, however, insufficient evidence to modify current clinical practice in regard to such LT candidates. For persons with end-stage OLD, LT may be the only therapeutic option.
- Lung transplantation for occupational lung diseases is relatively rare in the USA, representing 0.5% of all transplants performed.
- Subjects undergoing lung transplantation for occupational lung diseases appear to be at risk for poorer survival in the first post-transplant year.
- This first post-transplant year risk appears to be restricted to those subjects undergoing lung transplantation for non-silicotic occupational lung diseases.