Another Way of Looking at Delusions of Parasitosis
For the first 10 years of my practice, I treated delusions of parasitosis (DOP) the way I was taught in residency: Listen closely to the patient’s complaints; try to build a strong doctor-patient relationship; discuss the likely neuropathic cause of the sensations; do appropriate biopsies to rule out other diagnoses; and so on, in the hope that I’d eventually be able to get them to take pimozide.
Not a single patient ever took the pimozide, no matter how hard I tried to establish that relationship and do precisely what I had been taught to do.
Then, I had this conversation with a patient.
Patient: “Dr. Zirwas, why do you talk about this like I don’t have an infection?”
Me: “Because medical science has proven that no organism exists that causes an infection like this.”
Patient: “I was a philosophy major in college. That is a fallacy. It is impossible to prove something doesn’t exist.”
Me: “Interesting….”
So, I went home and looked it up. And the patient was right. It is impossible to prove something doesn’t exist.
I got interested enough to do some research on pimozide and its effectiveness for delusions, and it turned out that it doesn’t work.[1] In addition, the microbiologic investigation had shown that pimozide does have efficacy against intracellular infections.[2]
Obviously, I was aware of the fact that stomach ulcers had been considered primarily a psychologically caused problem until medical science advanced to the point of being able to identify that it was actually an infection with H. pylori.
The next time I saw a patient with DOP, I told [the patient] that medical science hadn’t been able to find any organism that was causing [this] disease. But it is possible that medical science just hasn’t advanced to the point of being able to identify it, and that I didn’t know if it was an infection or not. But there was a drug that studies had shown worked really well, called pimozide, which had been shown to work as an antibiotic, even though most doctors think of it as a psychiatric medication. I told [the patient] I was willing to prescribe it and see if it would help, and if it did, we wouldn’t know if it was working as an antibiotic or not. But at least [it] would be working.
[The patient] enthusiastically accepted the prescription and started on the pimozide at 1 mg bid. It was like magic. It worked so quickly and so well.
Since then, I’ve started calling DOP by an alternate name, “concern for non-observable infestation” and discussing it with patients as described above. In addition, I tell patients that with as rapidly and well as the pimozide works, it seems more like it is working as an antibiotic rather than as a psychiatric medication. Patients universally want to take the pimozide and it works wonderfully.
My experience has been that the possible infection is 75% less active in a month and 95% less active in 3 months.
Unfortunately, if DOP is an infection, the pimozide is only suppressing it–not eliminating it, as I generally find that stopping the drug results in the process becoming more active again. Therefore, instead of trying to stop it, I try to find the minimal dose that continues to suppress the symptoms, which is usually 1 mg a day (either 1 mg at bedtime or 0.5 mg twice daily). In some patients, I do need to continue the pimozide long term at 1 mg twice daily or the disease recurs.
The main takeaway is that by admitting that doctors don’t know everything, and that it is at least possible they do have an infection, I’ve gone from not being able to help a single patient (because they wouldn’t take the pimozide) to being able to literally change many lives. The drug allows them to go back to being a “normal” person rather than someone consumed by a presumed infection.
Incidentally, the most common question I get is “Can I spread this to other people if it is an infection?” To which I answer that I have never seen it spread from one person to another. So, if it is an infection, it appears that only certain people are susceptible to it.
In addition, I don’t look at or send off the samples they bring in with them anymore. I tell them that thousands of patients and doctors have looked at the samples and nothing is identifiable. If it is an infection, we just don’t have the tools to identify it.
I hope that this commentary on my experience gets more of my colleagues to rethink this disease and how we talk about it with our patients.
References:
1. Silva H, Jerez S, Ramirez A, et al. Effects of pimozide on the psychopathology of delusional disorder. Prog Neuropsychopharmacol Biol Psychiatry. 1998;22(2):331-340. doi:10.1016/s0278-5846(98)00008-6
2. Lieberman LA, Higgins DE. A small-molecule screen identifies the antipsychotic drug pimozide as an inhibitor of Listeria monocytogenes infection. Antimicrob Agents Chemother. 2009;53(2):756-764. doi:10.1128/AAC.00607-08.
