A vaper in the US has been diagnosed with a rare form of irreversible lung scarring usually caused by ingesting metals.
The diagnosis comes after a wave of deaths and illnesses linked to e-cigarettes, and has prompted calls for a rethink on whether the devices should be encouraged as a smoking cessation strategy.
The 49-year-old woman went to the doctor reporting shortness of breath and a dry cough, according to a case report in the latest issue of the European Respiratory Journal.
Doctors examining her soon found the cause - hard-metal pneumoconiosis, usually found in metal workers who regularly handle cobalt or tungsten.
"When we diagnose it, we are looking for occupational exposure to metal dust or vapour, usually cobalt, as a cause," said Kirk Jones, clinical professor of pathology at the University of California San Francisco.
"This patient did not have any known exposure to hard metal, so we identified the use of an e-cigarette as a possible cause."
Like most of those who have fallen ill or died in the US in recent months, the patient was vaporising a cannabis-based liquid.
While research into those cases has pinpointed vitamin E acetate as the culprit -a thickening agent used to dilute liquids to make them go further - this time it appears that metals in the e-cigarette device itself are being mixed into the toxic cloud the patient inhaled, thanks to the higher temperatures required to vaporise THC, the ingredient in cannabis which delivers the high.
"The presence of cobalt in the e-cigarette in this case could be related to differences in the material composition of the reservoir casing or the heating coil," the study said.
"Notably higher temperatures are required to aerosolise the active ingredient of cannabis oil, tetrahydrocannabinol (∼230C), in comparison to e-cigarettes, which aerosolise nicotine, ethylene glycol and glycerine at temperatures ranging from 110C to 185C."
No cobalt was found in the patient's lungs, but that's common in hard-metal pneumoconiosis cases as the body easily excretes it. Testing on the device showed cobalt was present in the vapour it produced, as well as other toxic metals such as nickel, aluminium, manganese, lead and chromium.
"This is the first known case of a metal-induced toxicity in the lung that has followed from vaping and it has resulted in long-term, probably permanent, scarring of the patient's lungs," said Rupal Shah, assistant professor of medicine at the University of California San Francisco.
The researchers said there are likely other people out there yet to be diagnosed with similar scarring, which often isn't noticed until it's too late to fix.
In an editorial published alongside the case study, European Respiratory Society president Jørgen Vestbo - a professor of respiratory medicine at the University of Manchester - said e-cigarettes "are harmful, they cause nicotine addiction and can never substitute for evidence-based smoking cessation tools".
"The medical profession as well as the public should be concerned about a new wave of lung diseases caused by a product which is heavily promoted by the tobacco industry."
As for the patient, she quit vaping immediately. Follow-up tests showed her lungs had lost volume and were showing signs of fibrosis and other evidence of lung disease.