Abstract

Recent case series and related commentary published in the AJRCCM, highlights the recent epidemic of acute lung injury associated with e-cigarettes use, and its remaining obscure nature. While this cluster is novel, pulmonary illness associated with e-cigarette use is not new: there are at least seven published case reports from 2012-2018 describing similar conditions in e-cigarette users and with no identifiable infectious etiology (i.e., acute lung injury, atypical pneumonitis, eosinophilic pneumonia, hypersensitivity pneumonia, lipoid pneumonia). Interestingly, of these seven reported cases, lung cell samples obtained via lavage or biopsy were available for five3-7, and all five exhibited abnormally lipid-laden macrophages. Lipid-laden macrophages were also a prominent feature (> 50%) in BAL of more recent case series from Utah. Such macrophages can trigger an inflammatory immune response leading to lipoid pneumonia, and other pneumonitis-like reactions. One report suggested that vegetable glycerin (VG) derived from vegetable oil and found in virtually all e-cigarette liquids is likely to be the exogenous source of lipid in an e-cigarette user diagnosed with lipoid pneumonia. However, most of the publications related to this new entity focused on tetrahydrocannabinol (THC), and a recent case series from the Mayo Clinic suggests chemical pneumonitis as a more probable etio-pathology. The fact that not all e-cigarette related lung injury cases were associated with THC use, and that THC “vaping” usually involves an oil vehicle (e.g. butane hash oils) do not rule out an important role for lipid-mediated lung injury in this clinical entity. This is particularly important to keep in mind given that most e-cigarette liquids contain VG as an essential component (helps make the e-cigarette aerosol visible). The implication is that many e-cigarette users, currently asymptomatic (or experiencing milder symptoms for which they do not seek medical attention), maybe undergoing lipid deposition in their airway, with concomitant inflammatory changes induced by lipid-laden macrophages and other immune cells. Therefore, we urge clinicians treating patients with acute and unexplained pulmonary complaints to identify if the patient is an e-cigarette user and, if so, to obtain detailed history about their use, and when possible to collect cell samples to determine if evidence of lipid exposure is present. Similarly, we urge researchers to investigate lipid exposure and inhaled toxic substances in e-cigarette users systematically. Most importantly, we call for regulators to implement immediately strict regulation that prevents lipid and inhaled toxicants emissions from all e-cigarettes sold in the US.

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