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Delusional parasitosis or Ekbom syndrome: a case series

To the Editor,

1. Introduction

Delusional parasitosis (DP) is a neuropsychiatric syn-

drome in which the patient has the fixed delusion of

infestation by parasites such as lice and mites [1]. Although

several cases have been recorded since the end of the 19th

century, it was the Swedish psychiatrist Karl-Axel Ekbom

who first studied systematically the presenile syndrome of

delusional dermatozoid parasitic infestation in 1938 [2].

After a multitude of different names being used over the

years such as acarophobia or parasitophobic neurodermatitis,

Ekbom’s name has become the eponym attached to the

condition referred to later as DP [2–4]. One reason for this

nomenclature change was the recognition that DP is not a

phobia, i.e., an irrational fear of being infested by parasites,

but rather a delusional condition. Some still debate whether

the primary disorder in DP is a tactile or cenestesic

hallucination precipitating a secondary delusion [3–6].

Delusional parasitosis is considered a rare condition in

neuropsychiatric settings. It has been mainly described in

case reports or small case series [6–8]. Delusional parasit-

osis patients usually seek dermatological care since the

presenting symptoms include several skin lesions such as

excoriations from scratching. Thus, some surveys performed

with dermatologists suggested that DP may be more

common than previous thought [9,10].

In this study, we report a Brazilian series of DP derived

from a psychiatric clinic.

2. Methods

All patients with DP seen by the authors since 1995

were carefully reviewed. The diagnosis of DP was based

on a detailed clinical history. The psychiatric classification

was done according to the structured clinical interview

Mini International Neuropsychiatric Interview [11,12]. The

Mini-Mental Status Examination (MMSE) was also

applied to all patients [13]. In order to exclude secondary

causes of DP, an extensive laboratory evaluation was

performed, including complete blood cell count; liver,

renal and thyroid function tests; serum electrolytes and

glucose levels; vitamin B12, folate and iron studies;

urinalysis; serological study for syphilis. Neuroimaging

studies were available for all subjects. Demographic data

were also obtained.

3. Results

Ten patients with DP were identified. The demographic

and clinical characteristics of the patients are depicted in

Table 1. Of the 10 patients, seven were female, resulting

in a female-to-male ratio of 2.3:1. The age at first clinical

evaluation ranged from 67 to 81 years (mean ageFS.D.,

72.4F5.2). Duration of symptoms ranged from 6 months

to 3 years, with a mean (FS.D.) of 18.0 (F9.4) months.

The mean (FS.D.) time of follow-up of patients was 9.9

(F2.8) months.

The presenting dermatological signs were considerably

variable, including excoriations from scratching, lichen-

ification, contact dermatitis to different topical products

applied. The bmatchbox sign,Q defined as the behavior of

bringing samples of the alleged parasites inside small

containers, was observed in just one patient (Case 9). The

phenomenon of folie a deux, i.e., shared delusion of

infestation by a partner, was not found in the present series.

Most patients were unmarried (widow, six; single, two)

or living alone (five). All had some clinical comorbidity,

mainly diabetes (four), hypertension (four) and thyroid

disease (three). None of the clinical illnesses could be

etiologically related to the diagnosis of DP. Five subjects

(50%) were diagnosed with a delusional disorder, a

primary psychotic category that cannot be attributed to

another major psychiatric disorder or physical illness

[14,15]. Two patients were diagnosed with major depres-

sion with psychotic symptoms, while another two with

dementia. One patient had a psychiatric background of

schizophrenia. The score in the MMSE was below the

expected value in three subjects (dementia, two; schizo-

phrenia, three). Of note, three patients exhibited patholog-

ical findings on neuroimaging studies, marked cortical

atrophy (Cases 8 and 10) and multiple small infarctions of

subcortical white matter (Case 7), which were compatible

with their diagnosis.

All patients used some antipsychotic medication in low

dose: half typical (haloperidol or pimozide) and half atypical

Letters to the Editor / General Hospital Psychiatry 28 (2006) 78–87 85

(olanzapine, quetiapine or risperidone). Two patients devel-

oped acathisia (Cases 1 and 8) and one significant

syalorrhea (Case 3). No other serious adverse effect was

noticed. Four subjects used antidepressants, and the patient

with Alzheimer’s disease also used the acetylcholinesterase

inhibitor rivastigmine. Full clinical remission of the

delusional symptom was obtained in six subjects, while

four had partial or no improvement.

4. Discussion

Our DP cases were etiologically categorized into three

main groups. The first group (50%) comprised a primary

psychotic disorder referred to as a delusional disorder of the

somatic type according to the present classification schemes

[14,15]. The second group (30%) was composed of other

functional psychiatric disorders such as depression and

schizophrenia that exhibited typical symptoms of DP. The

last group (20%) included DP secondary to a physical or a

neurological illness. In the present study, two cases were

associated with dementia, one with Alzheimer’s disease and

the other with vascular dementia.

Several organic conditions have been causally related to

DP, including substance abuse, infectious and endocrine

disorders [16,17]. Although DP is known to occur in a wide

variety of these physical illnessess, previous studies also

found a primary psychotic disorder as the main cause of DP

[8,18,19]. In our series, thyroid disease, diabetes, cardio-

vascular and pulmonary diseases were considered comorbid

conditions rather than etiological factors. The advanced age

of the patients studied (mean ageFS.D., 72.4F5.2 years)

may explain this high occurrence of comorbidities.

As the mean duration of symptoms was 18 months, the

average age at onset of the symptoms in the present series

would be over 60 years. Associated with the female

preponderance, the high frequency of social isolation

represented by many patients living alone — these are

the typical features of DP according to the literature

[8–10,17,18]. Thus, our series is consistent with previous

studies performed in different genetic and sociocultural

backgrounds. This reinforces the view that DP may be a

stable diagnostic category across different cultures. Another

relevant point is that the present series came from a

psychiatric clinic, while others were derived mainly from

dermatological services [8–10,17].

The outcome was favorable in six patients (60%), while

the remaining subjects (40%) had partial improvement or no

improvement. This picture is also compatible with other

studies [8,17,18]. In our series, we did not have considerable

adverse effects either with typical or with atypical anti-

psychotics. We cannot draw any conclusion about the

clinical superiority of a specific antipsychotic. Until

recently, pimozide was the drug of choice in the treatment

of DP [17]. Based on a better side-effect profile and

tolerability, atypical antipsychotics have been prescribed to

DP patients. There are some case reports on the use of

atypical antipsychotics, such as risperidone, quetiapine,

olanzapine in DP, but controlled studies are lacking [8,20].

Such studies may be difficult to perform, as DP is an

uncommon and heterogeneous syndrome.

In conclusion, rather than a unique illness, DP is a

neuropsychiatric syndrome that can follow primary psy-

chotic and depressive disorders, dementia or other organic

diseases. The typical patient is an elderly woman who is

Table 1

Demographic and clinical characteristics of the patients presenting with delusional parasitosis or Ekbom syndrome

Case Sex Age

(years)

Marital

status

Formal

education

(years)

Clinical

comorbidities

Psychiatric

diagnosis

(ICD-10 [14])

Duration of

symptoms

(months)

MMSE

[13] score

Treatment

(mg/day)

Outcome

(remission)

1 F 67 Widow 4 Hypertension F22 12 25 Risperidone (1) Partial

2 F 67 Widow 4 Hypertension,

diabetes

F22 24 26 Haloperidol (1.5) Complete

3 M 68 Widow 9 COPD F32.3 6 26 Haloperidol (1),

citalopram (20)

Partial

4 F 69 Widow 5 Hyperthyroidism F22 24 26 Olanzapine (5),

citalopram (20)

Complete

5 M 69 Married 3 Hypertension F32.2 12 24 Olanzapine (2.5),

moclobemide (300)

Complete

6 F 73 Single 7 Hypertension,

Diabetes

F22 36 27 Pimozide (2),

venlafaxine (75)

Complete

7 F 74 Single 4 Heart failure,

Hypothyroidism

F01 6 17 Risperidone (1) Complete

8 F 78 Widow 7 Hypertension,

Diabetes

F20 18 21 Haloperidol (2) Partial

9 F 78 Widow 6 Hyperthyroidism F22 24 26 Pimozide (2) No

improvement

10 M 81 Married 7 Heart failure F00 18 18 Quetiapine (100),

rivastigmine (12)

Complete

COPD, chronic obstructive pulmonary disease.

Letters to the Editor / General Hospital Psychiatry 28 (2006) 78–8786

unmarried or living alone. Clinicians should be alert to skin

lesions in these geriatric patients in order to exclude DP.

Rodrigo Nicolato, M.D.

Humberto Correa, M.D.

Department of Psychiatry, Faculty of Medicine

Federal University of Minas Gerais

Belo Horizonte 30130-100, Brazil

Marco A. Romano-Silva, M.D.

Department of Pharmacology

Institute of Biological Sciences

Federal University of Minas Gerais

Belo Horizonte 30130-100, Brazil

Antonio L. Teixeira Jr., M.D.

Department of Internal Medicine

Faculty of Medicine

Federal University of Minas Gerais

Belo Horizonte 30130-100, Brazil

E-mail address: altexr@gmail.com

doi:10.1016/j.genhosppsych.2005.08.008

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