By Philip R. Fischer, MD, DTM&H
Professor of Pediatrics, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN
SYNOPSIS: Delusional infestation, previously known as delusional parasitosis, is a condition with which patients believe that their bodies are infested with abnormal living organisms or non-living substances. Many patients can recover with a good therapeutic clinician-patient relationship and, usually, the use of risperidone, aripiprazole, or olanzapine.
SOURCES: Mendelsohn A, Sato T, Subedi A, Wurcel AG. State-of-the-art review: Evaluation and management of delusional infestation. Clin Infect Dis 2024; Jul 23:ciae250. doi: 10.1093/cid/ciae250. [Online ahead of print].
Mendelsohn A, Sato T, Subedi A, Wurcel A. Executive summary: Evaluation and management of delusional infestation. Clin Infect Dis 2024; Jul 23:ciae255. doi: 10.1093/cid/ciae255. [Online ahead of print].
Mendelsohn and colleagues from Tufts University in Boston provide a nice state-of-the-art review (and accompanying shorter executive summary) of delusional infestation for an upcoming issue of Clinical Infectious Diseases. While the condition remains challenging for patients and physicians, this new review provides updated information about the condition.
LABELING
Delusional infestation is a condition in which patients present believing that their bodies are infested with abnormal living organisms or non-living substances. This condition encompasses conditions that have previously gone by other names:
• acarophobia — described in the 1890s when patients believed they were infested by mites;
• Morgellons disease — itchy or bothersome skin symptoms associated with what are believed to be fibers extruding from the skin;
• Ekbom syndrome — as characterized in the Scandinavian literature in the 1930s;
• delusional parasitosis — a common term for the condition when it was linked to the belief that a parasitic infection or infestation was causing the symptoms; and
• delusional infestation — the common inclusive term for the condition used since 2009, regardless of whether the purported cause is a living organism and whether the symptoms relate to a specific body system.
INCIDENCE
A population-based study combined with a clinical review in the Midwestern United States published about 10 years ago suggested that the incidence of delusional infestation is 1.9 per 100,000 person-years. The mean age at diagnosis is 61 years. Women are 2.9 times as likely to be affected as men. Substance use disorder is disproportionately seen in individuals with delusional infestation, and anxiety and depression can occur along with delusional infestation. The diagnosis often is delayed, either by lack of recognition of the condition by medical care providers or by lack of acceptance of the diagnosis by patients.
PATHOPHYSIOLOGY
Delusional infestation can be a primary disorder, but it also can be secondary to a different underlying psychiatric or medical condition. There is some evidence that the condition might relate to dysregulation of dopamine. Several brain regions have been implicated in some studies, including the frontal, parietal, and temporal cortexes, as well as the dorsal striatum and the thalamus. Around 10% of patients with delusional infestation have a family member who concurrently experiences similar symptoms (“folie a deux” in French). Nonetheless, the pathophysiology of delusional infestation is not well understood.
EVALUATION
Patients often present fully convinced that they are infected or infested with specific microorganisms or inanimate objects. They might provide photos and/or samples of the identified “pathogens.”
A careful evaluation should be undertaken to identify any specific microbial infection or infestation as well as any environmental trigger of the symptoms. Scabies certainly can cause similar symptoms (with straightforward evaluation able to rule in or out this possibility). Organic medical conditions that can cause symptoms similar to those experienced by patients with delusional infestation include diabetes, thyroid disease, biliary disease, human immunodeficiency virus (HIV) infection, syphilis, and autoimmune disorders. Treatable organic pathology should be identified and managed, realizing that delusional infestation can coexist and overlap with some of these conditions.
Depending on the specific symptoms and physical exam findings, testing might include a blood count (looking for eosinophilia), liver and thyroid testing, a skin biopsy, and testing for parasites using tests for stool pathogens and specific serologies. Testing for HIV, Treponema, and toxins (in urine) could be considered, especially to rule out an organic basis for the symptoms.
Specialists sharing in the care of the patient should coordinate the communication of consistent messages for the patient and family. While the diagnosis is one of exclusion, that does not mean that negative test results should be explained as “there is nothing wrong.”
MANAGEMENT
The authors highlight the difficulty and importance of a “strong therapeutic relationship.” Patients often are very fixated on finding an infection-related or dermatologic diagnosis, and they might lose trust in the communicator of negative results. It is not often helpful to directly challenge the patient’s delusion, but there are ethical issues around failure to disclose a diagnosis of a delusional disorder. It is important to validate the patient’s experience while not validating the patient’s delusion. Clinicians can admit that they sometimes are unable to find the cause of a patient’s symptoms but often can help alleviate those symptoms anyway; following careful explanations, the patient might accept a symptom-focused treatment. A diagnosis of pruritus, for instance, with documentation about the lack of an identified infectious or dermatologic cause, might be most acceptable to the patient. In fact, an infectious disease specialist might be more successful in helping patients with delusional infestation, since patients might be reticent to work with a psychiatrist.
For patients with pruritus related to delusional infestation, antihistamines and topical steroids often are used. However, there is no convincing evidence that these treatments improve symptoms.
There are anecdotal reports that psychotherapy might help some patients with delusional infestation. However, there is not published evidence showing significant effectiveness of psychological therapies.
The primary treatment of delusional infestation is the use of second-generation antipsychotic agents. Psychiatrists are most familiar with the use of these medications and can help guide treatment, perhaps even remotely without seeing the patient. Patients can be informed that these medications are known to help with the patient’s sort of symptoms/infestation, whether or not this is explained as a psychiatric condition.
Some key tests should be done prior to the use of antipsychotic medications and then followed for possible adverse effects. Specifically, an electrocardiogram can help identify patients with prolonged QT intervals who might be at heightened risk of toxicity. Lipid profiles and blood sugar levels can be tested after an overnight fast. A blood count and metabolic profile also sometimes are suggested.
Either olanzapine (2.5 mg to 10 mg per day) or risperidone (0.5 mg to 4 mg per day) usually is provided as a first-choice medication. Aripiprazole (2 mg to 10 mg per day) is an alternative choice. Of course, careful explanation about the effectiveness of these medications for similar patients and reassurance that the patient does not have schizophrenia might help the patient accept using a medication that happens to be most commonly known as “antipsychotic.”
COMMENTARY
Fortunately, the outlook for patients with delusional infestation is not as grim as it once seemed to be. With newer antipsychotic medications, many patients recover from delusional infestation, even after having long-term symptoms. Of 52 patients with delusional infestation seen at a combined tropical medicine and psychiatry clinic (median age 57 years, 67% female, mean duration of symptoms 56 months), 58% continued follow-up, and 57% of those reported symptomatic improvement.1 The extent of improvement was associated with the degree of adherence to medication use.1
Similarly, in a retrospective, multicenter review of 156 patients (mean age 64 years, 61% female) with delusional infestation who complied with antipsychotic medication treatment, good response to treatment was noted in 57% taking risperidone, in 36% taking quetiapine, in 28% taking aripiprazole, and in 25% taking olanzapine.2
As mentioned by Mendelsohn and colleagues, there is some evidence that delusional infestation might be linked to disordered dopamine metabolism. In 2007, Huber and colleagues postulated that defective dopamine transport was responsible for delusional parasitosis based on the association of this delusion with toxic medications (including cocaine and amphetamine derivatives) and neurologic conditions (including Huntington’s disease) that involve dopamine.3 Some subsequent support for that hypothesis comes from structural studies of brain anatomy and from pre- and post-treatment functional imaging studies of the putamen and thalamus.4,5 However, the actual pathophysiology of delusional infestation has not yet been determined definitively.
The updated review by Mendelsohn and colleagues is helpful. Nonetheless, even though antipsychotic medication now can be effective for a majority of patients with delusional infestation, clinicians still face the challenge of getting patients to comply with recommended treatment.
REFERENCES
- Todd S, Squire SB, Bartlett R, Lepping P. Delusional infestation managed in a combined tropical medicine and psychiatry clinic. Trans R Soc Trop Med Hyg 2019;113:18-23.
- Tang PK, Lepping P, Lepping SG, et al. Efficacy of antipsychotics in delusional infestation. J Eur Acad Dermatol Venereol 2024; May 10. doi: 10.1111/jdv.20081. [Online ahead of print].
- Huber M, Kirchler E, Karner M, Pycha R. Delusional parasitosis and the dopamine transporter. A new insight of etiology? Med Hypotheses 2007;68:1351-1358.
- Wolf RC, Huber M, Depping MS, et al. Abnormal gray and white matter volume in delusional infestation. Prog Neuropsychopharmacol Biol Psychiatry 2013;46:19-24.
- Freudenmann RW, Kölle M, Huwe A, et al. Delusional infestation: Neural correlates and antipsychotic therapy investigated by multimodal neuroimaging. Prog Neuropsychopharmacol Biol Psychiatry 2010;34:1215-1222.
