REVIEW

Delusions of Parasitosis: An Update

Adam Reich . Dominika Kwiatkowska . Przemyslaw Pacan

Received: July 29, 2019 / Published online: September 13, 2019� The Author(s) 2019

ABSTRACT

Delusional parasitosis, also known as delusionalinfestation or Ekbom syndrome, is a relativelyinfrequent psychotic disorder characterized byan unwavering false belief that there is a para-sitic infestation of the skin, despite the absenceof any medical evidence that could support thisclaim. Delusional parasitosis can be categorizedinto primary, secondary, and organic forms.Sometimes, close relatives also experienceidentical delusions. This phenomenon wasreported to occur in 5–15% of cases, and isknown as shared psychotic disorder–delusionalparasitosis with folie a deux. Patients withdelusional parasitosis frequently seek help frommany physicians. Close multidisciplinarycooperation between clinicians is often key toshortening the time taken to diagnose this dis-order. Initiation of psychopharmacologicaltherapy is a challenge, as many patients refuseany psychiatric treatment because of the stigma

associated with mental illness and because oftheir firm belief that they have a parasiticinfestation, not a psychiatric condition. Formany patients, a sense of a lack of understand-ing leads to isolation and the development ofdepression symptoms, which is why it is crucialto earn the trust of such patients while takingcare of them.

Keywords: Delusional infestations; Delusionalparasitosis; Ekbom syndrome; Neuroleptics

INTRODUCTION

Delusional parasitosis, also known as delusionalinfestation or Ekbom syndrome, is a relativelyinfrequent psychotic disorder characterized byan unwavering false belief that there is a para-sitic infestation of the skin, despite the absenceof any medical evidence that could support thisclaim. The disorder is most frequently seen inmiddle-aged, often socially isolated, women(the average age is 57 ± 14 years) [1].

Delusional parasitosis can be categorizedinto primary, secondary (functional), andorganic forms. In primary delusional parasitosis,the patient has the delusion of being infestedwith parasites but no other psychiatric ororganic disorders is present. The secondary(functional) and organic forms of delusionalparasitosis occur secondarily to other disorders,

Enhanced Digital Features To view enhanced digitalfeatures for this article go to https://doi.org/10.6084/m9.figshare.9767597.

A. Reich (&) � D. KwiatkowskaUniwersytet Rzeszowski, Rzeszow, Polande-mail: adi_medicalis@go2.pl

P. PacanLower Silesian Mental Health Center, Wroclaw,Poland

Dermatol Ther (Heidelb) (2019) 9:631–638

https://doi.org/10.1007/s13555-019-00324-3

namely psychiatric and organic disease, respec-tively [2]. There are several mental disordersthat can be accompanied by Ekbom syndrome,such as schizophrenia, depression, dementia,anxiety, and phobia, while the organic type islinked with hypothyroidism, anemia, vitaminB12 deficiency, hepatitis, diabetes, infections(e.g., HIV, syphilis), and cocaine abuse [3].However, the exact etiology of this syndrome isyet to be determined. One possible reason forthis is false interpretation of the itching sensa-tion, which is a common symptom. A thoroughexamination is always necessary to rule outmany other diseases that may cause itching.Patients suffering from this delusion oftenreport other symptoms, such as formication,tingling, sensation of movement under theskin, or even pain, which are always associatedwith subjective certainty that the symptoms arecaused by the presence of worms, insects, orother parasites in the skin. These symptoms areinterpreted as tactile hallucinations or pares-thesia. Excoriation, discreet bruises, erosions,and cuts are frequent forms of self-damage thatare caused by attempts to remove parasites.Additionally, skin damage can be caused byobsessive cleansing and the application ofaggressive chemical or caustic substances toremove the fictitious parasite. To prove theinfestation, patients may bring to the physi-cian’s office a matchbox or another containerinto which the patient has placed various dustparticles, pieces of skin, fibers, etc. Samples ofthese materials are sent many times to variouslaboratories, which find no evidence of para-sites. This behavior is often called either‘‘matchbox sign,’’ ‘‘Ziploc bag sign,’’ or, morerecently, ‘‘specimen sign.’’

Sometimes, close relatives also experienceidentical delusions; this phenomenon is repor-ted to occur in 5–15% of cases and is known asshared psychotic disorder–delusional parasitosiswith folie a deux [4]. Interestingly, their symp-toms may disappear following their separationfrom the other person affected by delusionalparasitosis, but the majority of patients alsorequire psychotherapy and pharmacotherapy[5]. Media and the internet are also consideredimportant in the pathogenesis of shared

delusions, leading some to refer to this disorderas ‘‘folie a Internet.’’

Patients with delusional parasitosis fre-quently seek help from many physicians. Closemultidisciplinary cooperation between clini-cians is often key to shortening the time takento diagnose this disorder. Initiation of psy-chopharmacological therapy is a challenge, asmany patients refuse any psychiatric treatmentbecause of the stigma associated with mentalillness and also because of their firm belief thatthey have a parasitic infestation and not a psy-chiatric condition. For many patients, a sense ofa lack of understanding leads to isolation andthe development of depression symptoms,which is why it is crucial to earn the trust ofthese patients while taking care of them.

In the absence of randomized controlledtrials focusing on the effects of antipsychotics indelusional parasitosis, appropriate selection oftherapy is even more problematic. This reviewwas written in order to critically summarizecurrent therapeutic options for patients withdelusional parasitosis.

METHODS

Detailed searches of the PubMed and Clini-calTrials.gov databases were carried out for thiswork, using the following search terms: ‘delu-sional parasitosis,’ ‘delusional infestation,’ ‘pri-mary delusional parasitosis,’ ‘secondarydelusional parasitosis,’ ‘secondary functionaldelusional parasitosis,’ ‘secondary organicdelusional parasitosis,’ and ‘Morgellons disease.’Articles were selected based on their relevanceand by manual search of other paper references.All studies published in languages other thanEnglish were excluded. The research data had tobe published and to be available before July 1st,2019. Figure 1 provides data on the paperselection process. Importantly, the search of theClinicalTrials.gov database did not return anystudies of the disease of interest. This article isbased on previously conducted studies and doesnot contain any studies with human partici-pants or animals performed by any of theauthors.

632 Dermatol Ther (Heidelb) (2019) 9:631–638

Diagnosis

A thorough diagnostic examination is crucial tothe selection of an appropriate treatment of adisease with multiple etiologies. An actual par-asite infestation should always be excluded. Adetailed dermatological skin examination andthorough laboratory and microbiological testsas well as mineral oil skin scraping might aidthe differential diagnosis [6]. Nevertheless, anabsence of microscopic findings might not beconclusive if a history of exposure or typicalskin lesions such as burrows are present. On theother hand, it is also important to rememberthat parasitic skin diseases can manifest differ-ently and that skin lesions can be atypical [7].The clinical picture can also be changed bybacterial superinfections, which are often

caused by the patient’s self-manipulation. Afterruling out real parasitosis, one should analyzethe possible etiology of concomitant pruritus, ifpresent, including pruritus related to systemicdiseases. Furthermore, numerous medicinesmay cause subjective symptoms such as pruritusor formication, so a cautious review of allmedicines taken by the patient isrecommended.

Some other conditions on the dermatopsy-chiatric spectrum require consideration as partof the differential diagnosis. The skin lesions indermatillomania may be similar to thoseobserved in delusional parasitosis, but patientswith dermatillomania do not have a fixed beliefof an imaginary skin infestation. Suspicion ofdelusional parasitosis requires the exclusion ofother psychiatric disorders such as schizophre-nia, psychotic depression, dementia, affectivepsychoses, or obsessive–compulsive disorder.When these disorders are excluded, an allegedinfestation of parasites and the presence of the‘‘matchbox sign’’ may aid the diagnosis ofdelusional parasitosis. The exact type of delu-sional parasitosis should then be determined, asit is crucial to the selection of an appropriatetherapy. The secondary (functional) andorganic forms of delusional parasitosis alwaysrequire treatment of the underlying illness,while the primary form is usually treated withantipsychotics. Diagnostic steps for delusionalparasitosis are summarized in Figs. 2 and 3.

Pathophysiology

Still little is known about the neurobiologicalmechanisms that may be responsible for thesymptoms of delusional parasitosis. However,Huber et al. hypothesized that deterioratedfunctioning of striatal dopamine transporter(DAT), which also corresponds to an increasedextracellular dopamine level, could potentiallybe an important etiological factor for both(primary and secondary) forms of delusionalparasitosis [8]. DAT is a pivotal regulator ofdopamine reuptake in the brain, particularly inthe striatum. To support this claim, many casereports were investigated. It was found thatmedications that inhibit presynaptic dopamine

Fig. 1 Selection of publications for review analysis

Dermatol Ther (Heidelb) (2019) 9:631–638 633

Fig. 2 Diagnostic steps for delusional parasitosis

634 Dermatol Ther (Heidelb) (2019) 9:631–638

Fig. 3 Clinical subtypes of delusional parasitosis (modified by the authors from [6])

Dermatol Ther (Heidelb) (2019) 9:631–638 635

reuptake at the dopamine transporter (cocaine,amphetamines, pemoline, and methylpheni-date) can induce the symptoms of delusionalinfestation, such as formication. Moreover,many disorders, including schizophrenia,depression, traumatic brain injury, alcoholism,Parkinson’s and Huntington’s diseases, humanimmunodeficiency virus infection, and irondeficiency, all of which may cause secondary ororganic forms of delusional parasitosis, havebeen shown to involve diminished DAT func-tioning. It seems that antipsychotics couldimprove the symptoms of delusional parasitosisin the majority of patients by decreasing theabnormally high dopamine transmission.

Treatment Options

Since this disorder can have various potentialorigins, it is imperative to consider all possiblecauses of this disorder and to then select anappropriate therapy for the specific form ofdelusional parasitosis that the patient is suffer-ing from. Persistent symptoms such as delusionsare always an indication for the administrationof antipsychotic medications [9]. Studies eval-uating the disparity in efficacy between first-and second-generation antipsychotics in thetreatment of delusional parasitosis are lacking.Currently, second-generation antipsychoticssuch as risperidone or olanzapine are consid-ered first-line therapies, mostly due to theirsafer profiles and better tolerabilities.

When selecting the medicine, both the effi-cacy and possible side effects should be ana-lyzed in detail. All atypical antipsychotics couldcause metabolic dysfunction, so constantmonitoring of laboratory values during therapyis necessary. There is no known consensus onthe dosage of antipsychotics to use in cases ofdelusional parasitosis. In elderly patients, thedose should be adjusted for age as well as forkidney and liver function and the presence ofother chronic diseases. Dosages range between 1and 8 mg/day for risperidone and from 5 to10 mg/day for olanzapine [10]. In the criticalliterature review conducted by Freudenmannet al., risperidone and olanzapine were found tobe the most commonly used atypical

antipsychotics. Risperidone and olanzapine hada positive impact on 69% and 72% of thepatients under examination, respectively. Themaximum effect was achieved after at least6 months of therapy [11]. Many physicians donot recommend olanzapine as the first-linepharmacotherapy because of its metabolic sideeffects. A good alternative could be aripiprazole,which has the smallest side effect profile anddoes not cause weight gain. However, onlyseven case reports have described its efficacy indelusional parasitosis [7]. In most cases, thetherapy should be conducted long term in lowerdoses because discontinuation of the treatmentmay cause a recurrence of symptoms.

Over the years, administration of pimozideas a first-line treatment option has lost itsimportance due to concerns about its safetyprofile, its prolongation of the QTc interval, anda high risk of extrapyramidal symptoms [12]. Adouble-blind, placebo-controlled crossover trialcomprising 11 patients with delusional para-sitosis was performed in which the effects ofpimozide were evaluated. Pimozide turned outto be better than placebo at relieving the sen-sation of pruritus and delusions. However,‘‘feelings of vermin’’ and excoriations remainedunchanged [13]. In a case series of 33 patientswith delusional parasitosis, 18 of them receivedpimozide at dosages from 1 to 5 mg/day whilethe other 15 patients did not take the drug.Among patients receiving pimozide, 61%achieved improvement or complete remission,while the other 39% remained unchanged [14].Although pimozide has shown relatively goodefficacy in the majority of patients, its use issignificantly limited by its side effects. Regard-ing other first-generation antipsychotics,haloperidol, perphenazine, and sulpiride seemto be safer choices [15]. Depot antipsychoticsmight be considered when there is a concernabout the correct use of oral medications [16].

Depressive symptoms could be secondary todelusional parasitosis. Before starting pharma-cological treatment, patients with mild symp-toms should try cognitive behavioral therapy(CBT). CBT should focus on building patienttrust. CBT can help to create connectionsbetween the patient’s thoughts, emotions, andbehaviors [17]. The goal of CBT is to convince

636 Dermatol Ther (Heidelb) (2019) 9:631–638

the patient to start questioning their own fixedbeliefs, which can lead to significant improve-ments in the patient’s social life. Antidepres-sants might be necessary to relieve distress inpatients with moderate depressive symptoms.Selective serotonin reuptake inhibitors shouldbe first-line drugs. Escitalopram or sertralineseem to be good alternatives; combining themwith antipsychotics leads to the fewest sideeffects. In patients with delusional parasitosissecondary to medication-resistant depression,electroconvulsive therapy might be considered.

DISCUSSION

Delusional parasitosis is usually considered aninfrequent disorder. However, reliable epi-demiological data are limited, and the preva-lence of the disease is likely to have beenunderestimated [18]. According to Szepietowskiet al., 84.7% of dermatologists had seen at leastone patient with delusional parasitosis duringtheir professional career [19]. Such patientsusually seek help from dermatologists. There-fore, ensuring that physicians are fully versed inthe treatment of this disease is of the utmostimportance. Effective treatment requires a goodphysician–patient relationship [20]. Patientsshould always feel that their disease is beingtaken seriously; any discussion of the reality ofthe alleged parasite infestation is inadvisable.

As with many other skin conditions, delu-sional parasitosis has a negative impact on self-esteem. In order to assess the severity of theillness, it may be useful to evaluate the impair-ment of the patient’s quality of life. Once apositive relationship with the patient has beenestablished, a treatment may be suggested. It isusually easier for patients to accept a treatmentprescribed by a dermatologist rather than oneprescribed by a psychiatrist. A good way toconvince the patient to start therapy withantipsychotics is to introduce them as a treat-ment for the distress and itching [21]. Thepatient should be made aware that theantipsychotics are not prescribed to treatschizophrenia, and that many of the medica-tions commonly used in psychiatry are alsoused in dermatological practice due to the

presence of an antihistaminic component inmany antipsychotics. The majority of thesymptoms of delusional parasitosis disappearwhen the patient is receiving psychopharma-cological therapy. However, with delusionaldisorders, there is always a risk of recurrence.

Further research should focus on thoroughlyevaluating the current recommendations forthe treatment of delusional parasitosis. Apromising research direction in this field is thepossibility of using functional magnetic reso-nance imaging [22], as this could significantlybroaden the spectrum of dermatologicalresearch and enhance our understanding of theskin–brain connection. Gaining a detailedunderstanding of the exact pathophysiology ofdelusional parasitosis could facilitate thedevelopment of novel treatment modalities.

ACKNOWLEDGEMENTS

Funding. No funding or sponsorship wasreceived for this study or publication of thisarticle.

Authorship. All named authors meet theInternational Committee of Medical JournalEditors (ICMJE) criteria for authorship for thisarticle, take responsibility for the integrity ofthe work as a whole, and have given theirapproval for this version to be published.

Disclosures. Adam Reich has worked as aconsultant or speaker for AbbVie, Bioderma,Celgene, Chema Elektromet, Eli Lilly, Gal-derma, Janssen, Leo Pharma, Medac, MenloTherapeutics, Novartis, Pierre-Fabre, Sandoz,and Trevi, and participated as Principal Inves-tigator or Subinvestigator in clinical trialssponsored by AbbVie, Drug Delivery SolutionsLtd, Galderma, Genentech, Janssen, KymabLimited, Leo Pharma, Menlo Therapeutics,MetrioPharm, MSD, Novartis, Pfizer, and Trevi.Dominika Kwiatkowska and Przemysław Pacanhave nothing to disclose. Adam Reich is amember of the journal’s Editorial Board.

Dermatol Ther (Heidelb) (2019) 9:631–638 637

Compliance with Ethics Guidelines. Thisarticle is based on previously conducted studiesand does not contain any studies with humanparticipants or animals performed by any of theauthors.

Data Availability. Data sharing is notapplicable to this article as no data sets weregenerated or analyzed during the current study.

Open Access. This article is distributedunder the terms of the Creative CommonsAttribution-NonCommercial 4.0 InternationalLicense (http://creativecommons.org/licenses/by-nc/4.0/), which permits any non-commercial use, distribution, and reproductionin any medium, provided you give appropriatecredit to the original author(s) and the source,provide a link to the Creative Commons license,and indicate if changes were made.

REFERENCES

1. Trabert W. 100 years of delusional parasitosis. Psy-chopathology. 1995;28:238–46.

2. Prakash J, Shashikumar R, Bhat PS, et al. Delusionalparasitosis: worms of the mind. Ind Psychiatry J.2012;21:72–4.

3. Alves CJM, Martelli ACC, Fogagnolo L, et al. Sec-ondary Ekbom syndrome to organic disorder: reportof three cases. An Bras Dermatol. 2010;85:541–4.

4. Harth W, Gieler U, Kusnir D, Tausk F. Clinicalmanagement in psychodermatology. Berlin:Springer; 2009.

5. Suresh Kumar PN, Subramanyam N, Thomas B,et al. Folie a deux. Indian J Psychiatry. 2005;47:164–6.

6. Lepping P, Freudenmann RW. Delusional parasito-sis: a new pathway for diagnosis and treatment.Clin Exp Dermatol. 2008;33:113–7.

7. Campbell EH, Elston DM, Hawthorne JD, et al.Diagnosis and management of delusional parasito-sis. J Am Acad Dermatol. 2019;80:1428–34.

8. Huber M, Kirchler E, Karner M, et al. Delusionalparasitosis and the dopamine transporter. A new

insight of etiology? Med Hypotheses. 2007;68:1351–8.

9. Freudenmann RW, Lepping P. Delusional infesta-tion. Clin Microbiol Rev. 2009;22:690–732.

10. Al-Imam AML. A systematic literature review ondelusional parasitosis. J Dermatology DermatologicSurg. 2016;20:5–14.

11. Freudenmann RW, Lepping P. Second-generationantipsychotics in primary and secondary delusionalparasitosis. J Clin Psychopharmacol. 2008;28:500–8.

12. Gupta MA, Vujcic B, Pur DR, et al. Use of antipsy-chotic drugs in dermatology. Clin Dermatol.2018;36:765–73.

13. Hamann K, Avnstorp C. Delusions of infestationtreated by pimozide: a double-blind crossover clin-ical study. Acta Derm Venereol. 1982;62:55–8.

14. Generali JA, Cada DJ. Pimozide: parasitosis (delu-sional). Hosp Pharm. 2014;49:134–5.

15. Harth W, Hermes B, Freudenmann RW. Morgellonsin dermatology. JDDG. 2010;8:234–42.

16. Lepping P, Russell I, Freudenmann RW. Antipsy-chotic treatment of primary delusional parasitosis.Br J Psychiatry. 2007;191:198–205.

17. Reszke R, Pacan P, Reich A, Szepietowski JC. Delu-sional infestation in clinical practice over a periodof two decades. Adv Dermatol Allergol 2019 (Inpress).

18. Kohorst JJ, Bailey CH, Andersen LK, et al. Preva-lence of delusional infestation—a population-basedstudy. JAMA Dermatology. 2018;154:615–7.

19. Szepietowski JC, Salomon J, Hrehorow E, et al.Delusional parasitosis in dermatological practice.J Eur Acad Dermatol Venereol. 2007;21:462–5.

20. Patel V, Koo JYM. Delusions of parasitosis. Sug-gested dialogue between dermatologist and patient.J Dermatolog Treat. 2015;26:456–60.

21. Lepping P, Huber M, Freudenmann RW. How toapproach delusional infestation. Br Med J.2015;350:h1328.

22. Mueller SM, Hogg S, Mueller JM, et al. Functionalmagnetic resonance imaging in dermatology: theskin, the brain and the invisible. Exp Dermatol.2017;26:845–53.

638 Dermatol Ther (Heidelb) (2019) 9:631–638