CHICAGO, Oct 2 (Reuters) - Doctors studying lung tissue from people with vaping-related injuries have 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.
They found that none of the cases had evidence of lipoid pneumonia, a rare diagnosis typically associated with people accidentally inhaling oils into their lungs.
Their finding, published on Wednesday as a letter in the New England Journal of Medicine, contradicted early results of a study of five patients in North Carolina, published on Sept. 6 in the CDC'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 THC. Several states have also banned some vaping products and flavorings in response to the outbreak.
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 the marijuana ingredient tetrahydrocannabinol or THC.
So far, 87 percent of 86 people in Illinois and Wisconsin who got sick from vaping admitted to having used e-cigarette products containing THC, but 71 percent 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.
In the study published on Wednesday, 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.
In their view, the changes in the lung samples 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 pulmonlogist 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 a toxin 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. (Reporting by Julie Steenhuysen; Editing by Cynthia Osterman)