Hundreds or thousands of cases of severe lung inflammation may be going undiagnosed by doctors failing to recognise a potential hidden trigger for dangerous breathing problems: feather bedding.
In a new case report, doctors describe the painful saga of a 43-year-old man in the UK who turned up to his doctor after experiencing three months of malaise, fatigue, and breathlessness.
Initially, he was thought to have a respiratory tract infection, but his symptoms soon worsened, to the point where he had to take weeks off work, and even walking between rooms in his house could leave him gasping for breath.
"I started getting dizzy spells on exertion," the anonymous patient recalls.
"I was unable to stand or walk for more than a few minutes at a time without feeling like I was going to pass out. Going upstairs to bed was a 30-minute activity, as I could only manage two stairs at a time and then needed to sit and rest."
After numerous visits to his doctor, the man's mysterious breathing problem remained unidentified. He lived in a warm, dry house, and his living environment was almost entirely free of mould.
The man owned a cat and a dog, but no birds, which is significant, since exposure to organic dust from bird feathers is a known trigger for hypersensitivity pneumonitis – an immune system disorder where the lungs become inflamed by substances that are breathed in.
In this case, living birds may not have been the issue, but feathers nonetheless were still the likely source of his problem.
Interviews with a respiratory specialist, Owen Dempsey from Aberdeen Royal Infirmary, revealed that the man had recently acquired a duvet and pillows containing feathers, which had replaced his previous synthetic bedding. That sole change is suspected to be the cause of the patient's subsequent misery.
"FDL is caused by inhalation of organic dust from duck or goose feathers found in duvets and pillows," Dempsey and team explain in the case report.
"Antigen inhalation triggers an immunological cascade, resulting in lung parenchymal inflammation. Repeated exposure may result in irreversible lung fibrosis."
In the case of the 43-year-old man, FDL was diagnosed by the abnormally high presence of antibodies to bird feather dust in his blood, and CT imaging that revealed a 'ground glass' mosaic pattern visible in his lungs, suggestive of hypersensitivity pneumonitis.
Fortunately for the patient, the removal of his feather-based bedding, together with a long course of steroid treatment, resulted in a rapid improvement in his condition.
"The steroids which were prescribed after diagnosis … had a transformative effect within two days," the patient says.
"I have thankfully been able to stop [the drugs] completely. My oxygen saturation level nowadays is regularly 97 to 98 percent which I understand to be normal for someone my age, and I have not had any dizzy turns since recovering."
It's a happy result for the patient, who is able to now put months of breathlessness and fatigue behind him.
But the researchers say FDL could be a much bigger problem than we know, as doctors could be failing to identify this rare and little-known condition – if they don't pick up on the potential trigger of feather bedding, hiding in plain sight in patients' bedrooms.
"The onset of symptoms following exposure to new feather duvets or pillows is widely variable, ranging from three weeks to five years," the authors write.
"Given its heterogeneous and non-specific presentation, HP is often challenging to diagnose. The key is taking a meticulous history."
The findings are reported in BMJ Case Reports.