Feb 24, 2021
John Koo, MD, and Scott A. Norton, MD, MPH, join host Lorenzo
Norris, MD, for this special edition of the Psychcast. This is a
crossover episode with our sister podcast, Dermatology
Koo is a psychiatrist and a dermatologist at the University of
California, San Francisco. He has no disclosures. Dr.
Norton is a dermatologist with the Uniformed Services
University of the Health Sciences in Bethesda, Md., and with George
Washington University, Washington. He has no disclosures.
They are featured in an
article on this topic online at MDedge.com/Psychiatry.
Norris is associate dean of student affairs and administration
at George Washington University. He has no disclosures.
- Delusional infestation or delusions of infestation, also known
as delusional parasitosis, is a fixed false belief that one has an
infestation of animate or inanimate pathogens, despite strong
evidence against infestation. Common precipitants of delusional
infestation include previous exposure to external or internal
parasites, stress, and travel. The condition is more common among
highly functional older women.
- A recent
study estimated the prevalence of delusional infestation as
1.9/100,000, though the condition is an area of limited study.
Delusional infestation is poorly recognized by physicians,
therapists, and families, which leads patients to search for an
external cause of the symptoms and contributes to distress for
patients and their loved ones.
- Patients with delusional parasitosis often lack insight into
their disease, and it can be difficult to persuade them to take the
recommended treatment of antipsychotics.
- Low-dose pimozide, a first-generation antipsychotic, is the
most common treatment for delusional infestation, particularly
because it does not have Food and Drug Administration approval as a
treatment for psychosis. Therefore, patients are less biased
against taking this medication.
- Delusions of infestation are a monosymptomatic hypochondriacal
psychosis in which the only delusion present is one of infestation,
and patients do not have other symptoms of psychotic spectrum
illness. Secondary delusions of infestation may occur in
individuals who use drugs, such as methamphetamine or cocaine, or
who have a primary psychotic disorder, such as schizophrenia.
- Delusions of infestation is related to Morgellons disease,
which is defined as a skin condition characterized by the presence
of “threads” or filaments that patients believe are embedded in
their skin and might be accompanied by stinging and itching
- Patients with delusions of infestation usually present to a
primary care physician or ED with symptoms of abnormal sensations
of their skin, including crawling sensations. In addition, patients
usually bring personal proof of their condition, such as a small
bag of “specimens,” including pieces of lint, threads, or scabs.
Some patients also bring in journals detailing the timing and
associated factors of their symptoms.
- Dr. Norton advises that physicians treating the patients with
delusions of infestation should mentally prepare themselves against
initial bias and set aside time for longer visits or several
follow-up visits. Dr. Norton starts with the premise that the
patient has an actual infestation or other underlying cause of
their pruritus and performs a thorough, full-body exam for
dermatologic conditions, and examines the materials patients bring
with them using a double-headed microscope – so that he and the
patient can look at the specimens together.
- Dr. Koo often tells patients that they have Morgellons disease
because it does not include the stigmatizing term of “delusional.”
He reframes Morgellons as an infestation that cannot be cured by
internal or external antiparasitic medications. He then pivots away
from etiology to validation of their emotions and eventually to
- Dr. Koo usually often starts treatment with pimozide because it
is an antipsychotic with FDA approval for Tourette syndrome – not
schizophrenia. This perceived absence of a connection of the
medication to psychiatric illness allows patients to be more open
to taking the medication.
- For primary delusional infestation, Dr. Koo starts with
pimozide. The dose, which is daily and taken orally, starts low at
0.5 mg and goes up by 0.5 mg every 2-4 weeks. The aim is to get up
to 3 mg per day. Low doses of pimozide and other antipsychotics
lead to decreased sensation of itching and formication. Dr. Koo
refers to his treatment plan as a “trapezoid-like dosage strategy.”
Once he gets the patient to 3 mg, he continues the medication until
all the symptoms disappear and then continues the medication for an
additional 3 months. Dr. Koo then slowly tapers the dosage over an
additional few months.
- The keys to successful treatment include communicating with
patients and working collaboratively with them. This approach
builds trust and rapport.
Brown GE et al.
J Clin Exp Dermatol Res. 2014;5:6. doi:
Kohorst JJ et al.
JAMA Dermatol. 2018 May 1;154(5):615-7.
Lepping P et al. J Am
Acad Dermatol. 2017 Oct;77(4):778-9.
Middelveen MJ et al. Clin Cosmet
Investig Dermatol. 2018;11:71-90.
Lepping P et al. Acta Derm Venereol. 2020 Sep 16.
Freudenmann RW et al.
Br J Dermatol. 2012 Aug;167(2):247-51.
Wolf RC et al. Neuropsychobiology.
Show notes by Jacqueline Posada, MD, associate producer of the
Psychcast; assistant clinical professor in the department of
psychiatry and behavioral sciences at George Washington University,
Washington; and staff physician at George Washington Medical
Faculty Associates, also in Washington. Dr. Posada has no conflicts
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