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The Curious Case of Delusional Parasitosis

April 18, 2022

The Curious Case of Delusional Parasitosis

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I’m not too fond of bugs. I understand their importance in our ecosystems, and I appreciate them in an abstract sense. However, I’ve lived through several ant, house fly, and spider infestations while staying in rundown rental properties. There is no poorer sleep than having tiny insects as your bedfellows. Even thinking about the critters evokes phantom sensations of chitinous legs marching on my skin. To me, this emphasizes the power of our brains to create tactile sensations even in the absence of outside stimuli. 

But imagine that you felt like insects were crawling under your skin continuously, and that no one else, except maybe your partner, acknowledged it. This is the reality that patients with Delusions of Parasitosis face. 
In Delusions of Parasitosis, patients believe that they are infested with parasites, despite evidence to the contrary. They fail multiple medical therapies with topical treatments and oral anti-parasitic medications, and physical exams and lab tests do not corroborate their symptoms. Dejected by one office visit after another, patients spend a small fortune seeing different health care providers, trying various unguents, hiring fumigators, or even buying hazmat suits. Sometimes, partners and close family members are drawn into the patient’s beliefs, leading to a shared delusion called folie à deux (“folly of two” in French).

Although Delusions of Parasitosis is not a skin condition, patients often have bruises, scratches, cuts, and rashes in attempts to extricate their imagined parasites. Thus, primary care providers often refer patients to dermatologists for further workup and treatment.
On their first visit, patients with Delusions of Parasitosis often bring in a bag or box containing a collection of tiny particles—usually pieces of skin, scabs, and clothing fibers—in an attempt to prove their self-diagnosis. This event is so common that physicians have dubbed the phenomenon the “Ziploc bag sign.” By using an office microscope or sending the material to outside laboratories, healthcare providers can show that the particles are not parasites, but confronting the patients’ delusions does little to alleviate their discomfort. In fact, the discrepancy between the patient’s symptoms and the diagnosis creates a sense of isolation from the medical community. 

As a part of their training, dermatologists learn how to diagnose both parasitic infections and Delusions of Parasitosis. To diagnose the latter, a dermatologist has to rule out other medical or psychiatric conditions that could cause similar symptoms. Doctors order a number of lab tests and even take a piece of skin the size of a pencil eraser to look under the microscope.

Definitive diagnosis takes time and effort, and the treatment of Delusions of Parasitosis is even more difficult. It requires maintaining rapport by validating the patient’s distress without validating their delusion. It’s a fine rhetorical line to walk. Over multiple visits, dermatologists have to gauge the patient’s level of insight and nudge them to consider other causes for their discomfort. Many physicians feel out of their depth, as treating Delusions of Parasitosis often takes a significant amount of time and emotional investment.

Currently, the most effective therapy is starting on antipsychotic medications while continuing to follow up with dermatology to address skin symptoms. Therefore, treating Delusions of Parasitosis requires close cooperation between dermatologists and psychiatrists. Patients with Delusions of Parasitosis may be reluctant to start psychopharmacological therapy due to the stigma associated with mental illness and their unshakeable belief in their condition. 

Delusions of Parasitosis represents a breakdown in the patient’s perception of reality, thereby leading to mental distress, isolation, and frustration. Judging by the effectiveness of antipsychotics and the similarity of symptoms across patients, the condition probably reflects a process in the brain that scientists have yet to identify (like so many other medical and psychiatric conditions). Yet the treatment often requires more from the practitioners than just a prescription; it requires a willingness to engage with the patient, to show that they care even if the treatment isn’t what the patients think it needs to be. It’s a complicated condition that demands the best characteristics of physicians—patience, care, and communication—and a willingness of patients to trust and change their minds. 


What if you felt as if you were infested with parasites but no one believed you?

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Patients with Delusions of Parasitosis feel as if they are infested with parasites, despite evidence to the contrary.
Among patients with Delusions of Parasitosis, the discrepancy between the their symptoms and diagnosis creates a sense of isolation.
Treating Delusions of Parasitosis requires close cooperation between dermatologists and psychiatrists.

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