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General Hospital Psychiatry 32 (2010) 210–212

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Iatrogenic delusional parasitosis: a case of physician–patient folie a deuxJessica E. Bury, B.S.a, J. Michael Bostwick, M.D.b,⁎

aMayo Medical School, Mayo Clinic College of Medicine, USAbMayo Clinic College of Medicine, USA

Received 7 September 2009; accepted 30 September 2009

Abstract

This report presents a patient incorrectly diagnosed first with parasitic infestation and then with primary delusional parasitosis (DP).Neither diagnosis was correct. As she traveled from doctor to doctor, however, the primary DP label gained credibility via repetition, with herongoing symptoms seen as proof of its truth.© 2010 Elsevier Inc. All rights reserved.

1. Introduction

In 1799, Willan described the condition later known asdelusional parasitosis (DP), an unshakeable belief that one isparasite-infested, despite objective evidence [1,2]. Over thenext century and a half, the disorder carried many names,including acarophobia, dermatophobia, parasitophobia,entomophobia and Ekbom's syndrome [3,4]. Not until1946 did Wilson and Miller coin the term delusions ofparasitosis [5,6].

Recent reports implicate structural abnormalities anddopaminergic dysfunction in the striatum — specifically theputamen— in the etiology of DP [7]. Three lines of evidencesupport striatal abnormalities: (a) The putamen mediatesvisuo-tactile perceptions whose derangement is a central DPcharacteristic [7]. (b) Intoxication with dopaminergic drugsincluding cocaine, methylphenidate and methamphetamineis associated with tactile sensations suggestive of insects orparasites [7]. (c) Antidopaminergic antipsychotics haveshown effectiveness in reducing the intensity of delusion-driving sensations [2].

DSM-IV-TR classifies DP as a somatic form of mono-delusional disorder. Yet, evidence that DP and similar

⁎ Corresponding author. Tel.: +1 507 284 3789.E-mail address: bostwick.john@mayo.edu (J.M. Bostwick).

0163-8343/$ – see front matter © 2010 Elsevier Inc. All rights reserved.doi:10.1016/j.genhosppsych.2009.09.013

syndromes involving fixed beliefs of fibers or other materialsimbedded in the skin can signify an underlying illnesscausing tactile sensations attributed to these putativematerials continues to mount. In these cases, for which thedifferential is huge (see Table 1), the diagnosis is secondaryDP [12].

We describe what happened when physicians convinced apreviously unsuspecting patient that she had parasites. Mrs.B's “delusion” evolved from their assertions combined withher trust in the “white coat”. This folly led subsequentphysicians, in the absence of insect evidence, to conclude—logically but erroneously — that Mrs. B had a primarydelusional disorder. Other than a 1952 description of twosymptomatic patients unconvinced that they were parasite-infested until physicians told them they were, neitherPubMed nor Ovid/Medline contains reports of what we arecalling “iatrogenic delusional parasitosis” [5].

2. Case presentation

Mrs. B. had first presented with folliculitis for which shereceived intravenous antibiotics locally. After treatment, stillscratching, she sought help at “a doc-in-the-box”. The doctorinformed her that she had lice— even extracting a specimenfrom her hair to prove it— and prescribed lindane. (She laterconfessed that, to her, the specimen resembled nothing more

Table 1Causes of secondary DP/generalized pruritus [7–11]

DermatologicInsect bite reaction or infestationChronic folliculitisDermatitis herpetiformisPsychiatricSchizophrenia spectrum disordersAffective disorders with psychotic featuresAnxiety disorders, particularly obsessive–compulsive disorderHematologic/OncologicSevere anemiaLymphoproliferative disorders, lymphomaMyeloproliferative disorders, multiple myelomaBreast cancerMetabolicUremiaCholestasisCarcinoid syndromeEndocrineDiabetes mellitusHyper- or hypothyroidismHyper- or hypoparathyroidismSubstance abuseCocaineAmphetaminesAlcohol withdrawal (DTs)InfectiousAIDSHepatitisSyphilisTuberculosisMeningitis/EncephalitisNeurologicNeuropathiesParkinson's diseaseHuntington's diseaseMultiple sclerosisCerebrovascular accidentTraumatic brain injuryDementia

able 2aboratory investigation of secondary causes of DP [11,14,15]

omplete blood count and differentialiver function testshyroid function testserum electrolyteserum calciumlood glucoselood urea nitrogenerum creatinineitamin B12

olateon studiesrinalysisrine toxic screenge-appropriate cancer screening

211J.E. Bury, J.M. Bostwick / General Hospital Psychiatry 32 (2010) 210–212

than “a flake of skin”.) When lindane did not relieve heritching, another urgent care doctor told her that the firstdoctor had been mistaken; what she actually had were mites.He recommended permethrin. On her own, she escalated heruse to six bottles a month, treatment that did not help andmay have worsened her pruritus.

Although lindane and permethrin were ineffective, theydid reinforce her belief that she was infested. Like many DPpatients, she began seeking an explanation fitting aninfestation narrative. Having heard news reports abouthotel lice in a city she had recently visited, she wonderedif she could have acquired them there. Alternately, sheworried that her hairdresser or a grandchild with school-acquired lice could have infected her. She isolated herself forfear of transmitting lice to others. When shopping, she worea face-obscuring hat to hide blemishes from her gouging atitching skin. As doctors had instructed, she repeatedlywashed her linens and cleaned her home in hopes ofeliminating the lice. After 2 months, she finally saw a

dermatologist who discerned no evidence of lice despite herinsistence she had them, proposed a DP diagnosis andreferred her for a second opinion.

Mrs. B. arrived at our institution with a positive“matchbox sign”, material in a sandwich bag that she insistedwas insect-related [13]. Her examination revealed excoria-tions— some healed, some hemorrhagic— on her face, armsand lower leg— but no evidence of either lice or mites.Whena punch biopsy showed only necrotizing folliculitis andfungal and microorganism cultures were negative, thedermatologist concurred with the DP diagnosis. Unliketypical DP patients, Mrs. B readily agreed to see a psychiatristwho reaffirmed the diagnosis and prescribed pimozide.

Later, while reviewing outside records, the dermatologistnoticed previous elevated serum calcium levels of 11.1 and11.2. When a repeat calcium level was 11.6, he consulted anendocrinologist who quickly diagnosed primary hyperpara-thyroidism with hypercalcemia-induced itching. A monthafter parathyroidectomy, Mrs. B was “doing better, skinwise”. Several months later, off pimozide and topical agents,she endorsed neither itching nor delusions. She eventuallyrecalled that the urgent care doctors, rather than she, firstthought she had bugs. “They set it in my mind that it mightbe a parasite,” she said. If a doctor says it, it must be true.

3. Discussion

Ailments are deemed “functional” only after extensiveevaluation and laboratory investigation (see Table 2), fromwhich no physiologic explanation emerges [16]. DP is onesuch functional diagnosis, although only 40% of DP patientsactually have the primary form, a monodelusional disorderarising without explanatory underlying disease [2,17]. Anappropriate workup should rule out a multitude of knownskin symptom etiologies — including actual parasites —before diagnosing primary DP [18,19]. If an etiology isfound, the diagnosis is secondary DP. Our case is distinctfrom typical secondary DP, however, in that when the patientfirst presented, she did not believe she had parasites.

TL

CLTSSBBSVFIrUUA

212 J.E. Bury, J.M. Bostwick / General Hospital Psychiatry 32 (2010) 210–212

Although rigorous trials are lacking, current treatmentincludes both typical and atypical antipsychotics [2,16].Unfortunately, when referred to psychiatrists, DP patientsoften skip the consultations, leaving care entirely. As in otherdelusional disorders, a diplomatic and gingerly approach isadvised when making a psychiatric referral [5]. Patients stillregularly reject such care [1].

Mrs. B's story shows what happens when physiciansrepeatedly get it wrong. Hypercalcemia, not parasites, wouldeventually prove to explain Mrs. B's pruritus. Like a “good”patient, however, she deferred to physicians' perceivedexpertise. They told her she had bugs; she believed them.When they said she was delusional, she also believed that,providing her own delusional elaboration. Despite contra-dictory evidence, each subsequent doctor deferred topredecessors, transmitting false history as truth.

This case demonstrates a medical diagnosis explainingnew-onset delusions. It portrays evolving iatrogenic psy-chosis, created from incorrect diagnoses and reinforced byinappropriate treatments. Finally, it illustrates a twist on foliea deux, a delusional belief usually shared with a spouse orclose relative, though in this case, the “deux” is the patientand her physicians. Ultimately, the case underscores theimportance of “physicianly” skepticism before settling on“functional” diagnoses, particularly when organic workupshave been inadequate. Physicians must also have thehumility to recognize when they have taken an incorrectpath and the courage to reset their course.

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