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How to Treat Delusions of Parasitosis


Dr. Matthew Zirwas teaches the audience how he handles patients with Delusions of Parasitosis during his lecture at the SDPA 2014 Fall Conference in San Diego.


The patient comes to your clinic with a little jar filled with “bugs” that they took from their skin.  They’re either real bugs, or, more likely, the office is about to treat a patient with Delusions of Parasitosis.

Dr. Matthew Zirwas shared with the audience how he handles these patients during his lecture at the SDPA 2014 Fall Conference in San Diego.


Q: What is the key to helping people with delusions of parasitosis?

A: Understanding their delusion?

The likelihood that you can convince them that they don’t have bugs on their skin would be like trying to convince yourself that the sun is not in the sky.  You are sure of the sun.  They are sure of the bugs.


A Classification System

Grade 1:

They think there are bugs because they feel something like bugs on their skin, but they don’t have much of a story to go with it. 

Grade 2:

They are certain there are bugs on their skin and have extensive explanations to go with the belief, but seem totally normal besides when talking about the bugs. 

Grade 3:?

                True psychosis.  Severe long term socioeconomic impairment.


Dr. Zirwas explains that the management approach depends on the grade.


Stage 1

Not really delusional:

  • Explain that formication is an abnormal sensation caused by abnormal nerve functioning in the skin
  • Treat topically or with meds described for generalized pruritus


Stage 2?

Don’t tell them that the bugs don’t exist.

  • You will NEVER convince them, no matter what, and you make it much less likely that you’ll be able to help them

Don’t tell them that the bugs do exist.

  • They will expect you to go to the ends of the earth to identify them and kill the bugs.


Explain the situation to the Stage 2 patient:

  1. You’ve seen a lot of patients with a similar problem. Hundreds of thousands of people have this problem.
  2. Neither you nor anyone else (including the CDC) knows what causes it.
  3. Typical things that kill organisms have never worked for a single patient: insecticides, permethrin, ivermectin, bleach, gasoline, paint thinner, etc.
  4. Most insecticides work by targeting neurotransmitters in the organism and paralyzing them.
  5. The only treatment that has ever been reported to work targets neurotransmitters.
  6. It;s not known if it works because it affects neurotransmitters in the organism so they move less or die OR if it affects neurotransmitters in patient so they notice the organism less.
  7. The medication is called pimozide. It is usually used in humans to treat something called Tourette Syndrome, which “you, itchy patient, do not have.” 
  8. If they want to try it, you are willing to give it to them for a month, and then they have to come back so you can see how it is working.
  9. It does have some risk for side effects, so if it is working, they will need some testing if they want to stay on it.
  10. Do ask about a history of arrhythmia or heart disease, and if present, you should get an EKG before starting.
  11. Start pimozide at 1 mg bid.


Stage 3

This patient needs different treatment

Generally they have severe socioeconomic distress ?due to mental illness

Do not try to treat them

  • Communicate with their psychiatrist and social worker and make sure they know there are no bugs.


And good luck!

Image: origami_potato


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