Doctors studying lung tissue from people with vaping-related injuries have nearly ruled out one diagnosis as a probable explanation of how vaping harms the lungs, but the mystery over the exact cause only deepened.



Pathologists from the Mayo Clinic studied lung biopsies from 17 patients in the vaping-related outbreak that has sickened more than 800 and claimed the lives of 16 people in 13 U.S. states.

In Canada, a Quebec resident has been diagnosed as the country's first case of a severe vaping-related breathing illness.

The U.S. researchers found that none of the cases had evidence of lipoid pneumonia, a rare diagnosis typically associated with people accidentally inhaling oils into their lungs.

In the study published as a letter Wednesday in the New England Journal of Medicine, Mayo's Dr. Brandon Larsen and colleagues found no evidence of lipoid pneumonia in any samples they studied.

They suggest that the presence of oil in the lungs may simply be a marker of vaping exposure and not the cause of vaping-related illnesses.



Their findings differ from early results of a study of five patients in North Carolina, published on Sept. 6 in the Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report.



In those cases, doctors examined lung samples from patients with severe lung injury and found immune system cells called macrophages filled with oil. They diagnosed all five with lipoid pneumonia.



The illnesses have prompted a health scare that has led U.S. officials to urge people to stop vaping, especially products containing tetrahydrocannabinol or THC, the marijuana ingredient that produces a high. Several states have also banned some vaping products and flavourings in response to the outbreak.

New letter describes 17 patients, all of whom vaped, who had lung biopsies after presenting with symptoms and bilateral pulmonary opacities that led to a clinical diagnosis of <a href="https://twitter.com/hashtag/vaping?src=hash&ref_src=twsrc%5Etfw">#vaping</a>-associated lung injury. <a href="https://t.co/n5rF2OOOwq">https://t.co/n5rF2OOOwq</a> —@NEJM



Scientists have been working to understand the role of these oil-filled cells, known as lipid-laden macrophages, to help explain how vaping can cause lung injuries in otherwise healthy adults.



One possibility is that the oil is coming directly from oils inhaled in vaping devices, such as oils containing THC.



So far, 87 per cent of 86 people in Illinois and Wisconsin who got sick from vaping admitted to having used e-cigarette products containing THC, but 71 per cent also reported using nicotine-containing products.



Another theory, backed by studies in mice, is that in some patients, the fat-clogged immune cells are forming as part of the body's natural response to exposure to solvents or other chemicals used in vaping devices. Scientists have been working to understand the role of these oil-filled cells, known as lipid-laden macrophages, to help explain how vaping can cause lung injuries in otherwise healthy adults.One possibility is that the oil is coming directly from oils inhaled in vaping devices, such as oils containing THC.So far, 87 per cent of 86 people in Illinois and Wisconsin who got sick from vaping admitted to having used e-cigarette products containing THC, but 71 per cent also reported using nicotine-containing products.Another theory, backed by studies in mice, is that in some patients, the fat-clogged immune cells are forming as part of the body's natural response to exposure to solvents or other chemicals used in vaping devices.

Chemical irritant

The Mayo Clinic authors said the changes in the lung samples they saw suggest that the vaping-related injuries are caused by inhaling chemical irritants, but the specific agents are not known.

Dr. Jennifer Layden, chief epidemiologist in Illinois, one of the first states to report vaping-related illnesses, said lipid-laden macrophages were not a predominant characteristic in the 53 cases described by Illinois and Wisconsin last month in the New England Journal of Medicine.



Dr. Laura Crotty Alexander, a pulmonologist who studies vaping at University of California San Diego, said the Mayo findings are in line with other studies suggesting the injuries are related to toxic substances entering the lungs.



"This is just putting further emphasis on the fact that lipoid pneumonia is not the pathologic pattern being seen in this epidemic," she said in an email.

Canadian health officials say anyone who has used an e-cigarette or vaping products, and has symptoms such as shortness of breath, cough, chest pain, with or without vomiting, diarrhea, abdominal pain or fever is advised to consult a health-care professional.

People who switched to vaping to cut down on smoking cigarettes should not go back to cigarettes, Canadian health officials said.