Reduced Diffusing Capacity in Humidifier Disinfectant-Associated Asthma Versus Typical Asthma: A Retrospective Case...

Humidifier disinfectant-related lung injury (HDLI) is a severe form of toxic inhalational pulmonary parenchymal damage found in residents of South Korea previously exposed to specific guanidine-based compounds present in humidifier disinfectants (HD). HD-associated asthma (HDA), which is similar to irritant-induced asthma, has been recognized in victims with asthma-like symptoms and is probably caused by airway injury. In this study, diffusing capacity of the lung for carbon monoxide (DL_CO) in individuals with HDA was compared to that in individuals with pre-existing asthma without HD exposure.

We retrospectively compared data, including DL_CO values, of 70 patients with HDA with that of 79 patients having pre-existing asthma without any known exposure to HD (controls). Multiple linear regression analysis and logistic regression analysis were performed to confirm the association between HD exposure and DL_CO after controlling for confounding factors. The correlation between DL_CO and several indicators related to HD exposure was evaluated in patients with HDA.

The mean DL_CO was significantly lower in the HDA group than in the control group (81.9% vs. 88.6%; P = 0.021). The mean DL_CO of asthma patients with definite HD exposure was significantly lower than that of asthma patients with lesser exposure (P for trend = 0.002). In multivariable regression models, DL_CO in the HDA group decreased by 5.8%, and patients with HDA were 2.1-fold more likely to have a lower DL_CO than the controls. Pathway analysis showed that exposure to HD directly affected DL_CO values and indirectly affected its measurement through a decrease in the forced vital capacity (FVC). Correlation analysis indicated a significant inverse correlation between DL_CO% and cumulative HD exposure time.

DL_CO was lower in patients with HDA than in asthma patients without HD exposure, and decreased FVC partially mediated this effect. Therefore, monitoring the DL_CO may be useful for early diagnosis of HDA in patients with asthma symptoms and history of HD exposure.