Doctors may find these patients difficult, but there are some straightforward steps to managing delusions of parasitosis.
Patients with suspected delusional parasitosis should be treated dermatologically rather than being immediately referred to a psychiatrist or psychologist, says one expert.
When patients believe their skin is infested with insects, the cause is usually the feeling of itch, Associate Professor Samuel Zagarella told delegates at the Australasian College of Dermatologists’ annual scientific meeting in Brisbane earlier this month.
“Throughout history, humans have sought explanations for strange or unexplainable phenomena,” the University of Sydney dermatologist said. “If a plausible explanation is not readily available, the brain will conjure something up.”
Professor Zagarella said doctors needed to carefully investigate all causes of pruritis when a patient presented with suspected delusions of parasitosis.
“You don’t want to end up with egg on your face by making a diagnosis of delusions of parasitosis when a patient has a real cause of itch,” he said.
“So you must really carefully exclude scabies, body lice, head lice and bird mites – which I see all the time in Sydney in spring and summer.”
It was important to do the usual pruritis lab tests, such as a full blood count, B12, iron studies, renal function, EPG and IEPG, he said.
It was easy to think “this patient is crazy” when they presented their evidence of insect infestation, Professor Zagarella said.
“But you must discard your preconceptions and look at them closely, take a skin scraping from microscopy, and even a biopsy if indicated,” he said.
He said he firmly believed dermatologists should be managing these patients rather than psychiatrists – unless there was reason to believe there was a serious psychiatric comorbidity, like schizophrenia or bipolar. In that instance, it was appropriate to involve a psychiatrist.
“But most patients, in my experience, don’t have these psychiatric conditions,” he said.
After investigating the cause of the itch, excluding causes of pruritis and making a diagnosis of delusions of parasitosis, the next step was correct communication.
He tells patients, “All the tests I’ve done have not found any bugs or insects in your skin. I believe the nerves in your skin are hyperactive and are sending signals to your brain… It’s not just in your head. I really believe that you have a real problem, and we need to treat these overactive nerves in your skin. I can help you”.
Professor Zagarella said it was “amazing” how effective that approach could be. And he warned against either arguing with patients that this was all in their heads or enabling their delusion.
Several treatments had been particularly effective: daily moisturisers, antihistamines, low-strength corticosteroids and low-dose tricyclic antidepressants.
“These people spend a fortune on pest control – cans of Baygon that they spray on their mattress over and over and over again, poisoning themselves and their family with these toxic chemicals. So you must stop all of that,” he said.
“Avoid all antiseptics as well, such as Pine O Cleen and Dettol.”
Professor Zagarella said he found those measures adequate for most patients, but doctors could consider SSRIs or antipsychotics for the small proportion who continue to have issues.
