The British Journal of Psychiatry (2007) 191: 198-205. doi: 10.1192/bjp.bp.106.029660
© 2007 The Royal College of Psychiatrists
Antipsychotic treatment of primary delusional parasitosis
Systematic review
Peter Lepping, MD (FRG), MRCPsych, MSc
North Wales Section of Psychological Medicine, Wrexham Academic Unit,
Technology Park, Wrexham, Wales, UK
Ian Russell, PhD, FRCGP, FRCPEd, FFPH
Institute of Medical and Social Care Research, University of Wales
Bangor, Gwynedd, Wales, UK
Roland W. Freudenmann, MD (FRG)
Department of Psychiatry, University of Ulm, Ulm, Germany
Correspondence:
Dr Peter Lepping, North Wales Section of Psychological Medicine, Wrexham
Academic Unit, Technology Park, Wrexham, LL13 7YP, UK. Email:
peter.lepping{at}new-tr.wales.nhs.uk
Declaration of interest P.L. has received fees from Lilly, Otsuka
and AstraZeneca for educational talks.

ABSTRACT
Background Little is known about the treatment of delusional
parasitosis with typical and atypical antipsychotics.
Aims To evaluate the effectiveness of typical and atypical
antipsychotics in primary delusional parasitosis (delusional disorder, somatic
type).
Method A systematic review was conducted.
Results No randomised trials were found and hence we collected the
best evidence from 16 other trials and case reports, separating primary from
other forms of delusional parasitosis. Studies using typical antipsychotics
showed partial or full remission in between 60 and 100% of patients. Analysis
of selected patients with primary delusional parasitosis showed that typical
and atypical antipsychotics were effective in the majority, but that remission
rates did not differ significantly between typical and atypical
antipsychotics.
Conclusions In the absence of controlled trials there is limited
evidence that antipsychotics are effective in primary delusional parasitosis.
Rigorous studies are needed to evaluate their effectiveness and to compare
typical and atypical antipsychotics directly.

INTRODUCTION
Delusional parasitosis is characterised by the fixed belief
that one is
infested with parasites or small living creatures
although there is no medical
evidence for this (
Arnold,
2000;
Freudenmann,
2002). Patients usually complain about itching
that they ascribe
to the presence of animals in or under the
skin. The belief is usually held
with delusional intensity
but the severity of the delusional intensity can
vary. The
annual prevalence of delusional parasitosis is estimated at
80 cases
per million inhabitants, with a yearly incidence of
20 per million
(
Trabert, 1997).

History
It is usually said that delusional parasitosis was first described
by
Thibierge in 1894 and Perrin in 1896. However, according
to Trabert's
comprehensive historical literature search (Trabert,
1993,
1997), the clinical picture
was first mentioned by
Robert Willan in 1799 and Johann Heinrich Jördens
in 1801.
According to our research neither author suspected a psychiatric
aetology. Moreover, Musalek
(
1991) discovered a patient
with
delusions of
intestinal parasitosis (
Enterozoenwahn) in
an
article from 1843 (
Charcellay,
1843).

Pathogenesis
Delusional parasitosis is a non-specific syndrome rather than
a single
disorder. It can occur as a delusional disorder, meeting
ICD–10 criteria
for persistent delusional disorder (
World
Health Organization, 1993)
and DSM–IV–TR criteria for
delusional disorder,
somatic type (
American
Psychiatric Association, 2000). This
is what clinicians usually
mean when they refer to `delusional
parasitosis', although it accounts only
for about 40% of all
patients with such symptoms
(
Trabert, 1995). We will call
this
type of delusional parasitosis `primary delusional parasitosis'
following
Ganner & Lorenzi's (
1975)
concept of `
reiner Dermatozoenwahn' (German `
rein'=primary
or pure). The diagnosis
of primary delusional parasitosis can be made only
after real
infection or other underlying medical or psychiatric conditions
have been excluded, because delusional parasitosis can be associated
with
several physical illnesses, psychiatric disorders or intoxications
(
Magnan & Saury, 1889;
Ekbom, 1938;
Huber, 1957;
Berrios, 1985;
Freyne & Wrigley, 1994;
Freudenmann, 2002). Delusional
parasitosis can also occur as a
folie à deux or
folie
à trois (shared psychotic disorder;
Trabert, 1995)
as well as by
proxy (
Nel et al,
2001). Delusional parasitosis
syndromes can thus be classified
according to their pathogenesis
(Appendix 1).

Clinical management
The clinical management of patients with delusional parasitosis
is a
challenge, as patients are often reluctant to engage in
a meaningful
therapeutic relationship because of their somatic
concept of the illness. Thus
they seek help from general practitioners,
dermatologists or pest control
companies but refuse psychiatric
referral or therapy. Usually, it is difficult
to obtain informed
consent to treat patients with delusional parasitosis with
antipsychotics.
Therefore experienced clinicians tell their patients that the
antipsychotics are effective `against the itch' or the `problems
with the
pests' in order not to have to lie. A few practical
guidelines have been
proposed (
Musalek, 1991;
Driscoll et al, 1993;
Winsten, 1997;
Freudenmann, 2002).
Another approach to achieve a better therapeutic relationship was developed
in the late 1980s. Specialised out-patient clinics were located in
dermatology clinics to acknowledge the patients' non-psychiatric
concept of their illness (Musalek &
Kutzer, 1989; Musalek et
al, 1989; Musalek,
1991; Trabert,
1993). However, even these `low threshold' settings have often
failed to allow the establishment of a sufficient therapeutic alliance.
Trabert's study in Homburg, Germany stated that 20 of 35 patients (57%) were
seen for less than 3 months (Trabert,
1993). Despite all these efforts, many patients lose faith in
professional medicine and resort to dangerous self-therapies such as excessive
skin cleaning with chemicals or pesticides
(Freudenmann, 2002).

Antipsychotic treatment
For adequate treatment of delusional parasitosis it is necessary
to
differentiate between the different forms
(
Berrios, 1985;
Freudenmann & Schönfeldt-Lecuona,
2005). Although
antipsychotics provide the main treatment for
primary delusional
parasitosis, they are used only symptomatically for
delusional
parasitosis secondary to somatic diseases, which mainly requires
adequate therapy of the underlying disorder. Even in recent
years, many
sources recommended the use of the typical antipsychotic
pimozide in
delusional parasitosis (
Driscoll et
al, 1993;
van Vloten,
2003), although pimozide is no longer a first-line
antipsychotic
because of concerns about drug safety (high risk
of extrapyramidal symptoms,
longer QTc interval and drug–drug
interactions
(
Food and Drug Administration,
1996;
National Institute for
Clinical Excellence, 2002;
Benkert & Hippius,
2005).
Several case reports have indicated the beneficial effects of
atypical antipsychotics in primary delusional parasitosis, but
evidence for these is still limited to risperidone
(Gallucci & Beard, 1995;
Freyne et al, 1999;
Moretti & Varga, 2000),
quetiapine (Kim et al,
2003), olanzapine (Le &
Gonski, 2003) and amisulpride
(Lepping et al,
2005).
Although it is often stated that there is a lack of randomised controlled
trials of the use of antipsychotics (including pimozide) in delusional
parasitosis (Driscoll et al,
1993; Trabert,
1995; Freudenmann &
Schönfeldt-Lecuona, 2005), we know of no systematic review on
this topic. Moreover, no antipsychotic is licensed for the treatment of
delusional parasitosis. We therefore undertook the first systematic review of
the effectiveness of typical and atypical antipsychotic treatment for primary
delusional parasitosis (meeting ICD–10 F22.0 criteria for persistent
delusional disorder or DSM–IV–TR criteria for delusional disorder
of somatic type) in order to determine whether: typical
antipsychotics are effective in treating primary delusional parasitosis and
are more effective than placebo; atypical antipsychotics are
effective in treating primary delusional parasitosis and more effective than
placebo; atypical antipsychotics are more or less effective than typical
antipsychotics.

METHODS
Search strategy
Our first priority was to discover randomised controlled trials
that
addressed the study questions. We tried to identify all
available works on
delusional parasitosis published in English,
German, French, Spanish,
Portuguese, Italian, Dutch or Hungarian
before December 2005. A comprehensive
search of EMBASE, Medline,
PsycInfo, PsycLit and Psyndex was performed using
the search
terms `delusion(s) of parasitosis', `delusional parasitosis',
`delusion(s) of infestation', `
*parasitosis
*',
`monosymptomatic
hypochondriacal psychosis', `parasitophob
*',
`entomophob
*',
`acarophob
*', `Dermatozoenwahn', and
`Ekbom's syndrome' (discarding
papers on the `burning feet syndrome' which has
also been labelled
with this eponym). We checked the reference lists of
identified
articles. We searched the internet using Google, and textbooks
of
psychiatry, theses, unlisted journals and conference proceedings
by hand. We
wrote to pharmaceutical companies producing substances
often used to treat
delusional parasitosis and known authorities
in the field of delusional
parasitosis (e.g. Wolfgang Trabert,
Emden, Germany, and Marc Bourgeois,
Bordeaux, France) to identify
unpublished data on the use of antipsychotics in
delusional
parasitosis. We searched for continuing trials via two websites
– Clinical Trials
(
http://www.clinicaltrials.gov)
and
Current Controlled Trials
(
http://www.controlledtrials.com).
Assessment of literature
P.L. and R.W.F. independently assessed whether all retrieved works dealt
with delusional parasitosis in general or primary delusional parasitosis, and
whether the intervention consisted of typical or atypical antipsychotics. We
also assessed whether any of these were randomised controlled trials.
In the absence of randomised controlled trials we planned to gather sound
evidence from other studies meeting defined inclusion criteria (see Appendix
2). In particular we sought well-designed quasi-experimental and observational
studies relevant to our research questions. We included all open studies with
either prospective design or more than 30 patients. We then summarised in
structured form the main findings of the 16 studies meeting these minimal
criteria (Table DS1, data supplement to online version of this paper). We
assigned individual outcomes between three main categories: no effect (0);
partial remission (i.e. some response) (1) and full remission (2). To
strengthen our conclusions we also tried to separate primary delusional
parasitosis from secondary delusional parasitosis.
P.L. and R.W.F. also selected all case reports containing information on
diagnosis of primary delusional parasitosis, gender, age, antipsychotic
medication used and dose, and clinical outcome on the same 3-point scale after
4 weeks or more. In this way we applied Trabert's case-based meta-analysis
which is designed for uncommon syndromes that cannot be studied in a
traditional randomised controlled trial
(Trabert, 1995). We also
separated patients treated with typical and atypical antipsychotics. Although
this approach is subject to publication bias because it considers only
published cases, we aimed to increase comparability between studies. To judge
the success of this strategy we tested whether clinical outcomes differed
significantly between studies.

RESULTS
Literature search
We identified a total of 368 works on delusional parasitosis
in general,
including poster presentations, in December 2005
(
Fig. 1). We found most on
Medline (
n=191), and in review
articles and the comprehensive theses
of Musalek (
1991) and
Trabert
(
1993). At least half were not
in English –
most of these were in German, but some were in Italian and
French.
The full bibliography can be obtained from the authors on request.
Before the psychopharmacological era, which began with the discovery
of
chlorpromazine in 1952, only 31 works on delusional parasitosis
were
retrieved. The majority (
n=223) were published between
1952 and the
launch of risperidone in about 1990. The remainder
(
n=114) were
published after 1990, but many of these did not
examine the use of atypical
antipsychotics.
Absence of randomised controlled trials
Our systematic search found no randomised controlled trials on the
effects of typical or atypical antipsychotics in either primary or other
delusional parasitosis. When accessed in December 2005, the Clinical Trials
(http://www.clinicaltrials.gov)
and Current Controlled Trials
(http://www.controlled-trials.com)
websites gave no indication of unpublished or current randomised controlled
trials. Our evaluation of the literature therefore relied on results from
other studies.
Effect of typical antipsychotics
Table DS1 (see data supplement to online version of this paper) summarises
the 16 quasi-experimental or observational studies which primarily used
typical antipsychotics and met our inclusion criteria
(Frithz, 1979;
Hamann & Avnstorp, 1982;
Munro, 1982;
Lyell, 1983; Ungvari,
1983,
1984; Ungvari & Vladar,
1984,
1986;
Lindskov & Baadsgaard,
1985; Bourgeois, et
al, 1986; Reilly &
Batchelor, 1986; Musalek,
et al, 1989;
Paholpak, 1990; Trabert,
1993,
1995;
Srinivasan et al,
1994; Zomer et al,
1998; Bhatia et al,
2000). The studies showed aggregate partial and full remission
rates between 60 and 100% after treatment with typical antipsychotics.
Unfortunately, the majority were not limited to primary delusional
parasitosis. Nevertheless they suggest a generally good outcome for primary
and other forms of delusional parasitosis whenever continuous antipsychotic
treatment can be established.
In primary delusional parasitosis, aggregate partial and full remission
rates with pimozide ranged from 67 % (n=66;
Lyell, 1983) through 89%
(n=9; Munro, 1982) to
100% (n=10; Ungvari & Vladar,
1984,
1986), n=18; Ungvari,
1983,
1984). In mixed
samples with primary and other forms of delusional parasitosis, aggregate
partial and full remission rates with pimozide were similar and varied from
61% (n=33; Zomer et al,
1998), through 87% (n=52;
Bhatia et al, 2000)
to 91% (n=11; Hamann &
Avnstorp, 1982). A high rate of side-effects such as sedation,
extrapyramidal symptoms and depression was noted in several studies using
pimozide (38%; Ungvari, 1983,
1984 and 73%;
Hamann & Avnstorp,
1982).
The only two placebo-controlled trials in delusional parasitosis both used
pimozide (Hamann & Avnstorp,
1982; Ungvari & Vladar,
1984,
1986). However, they are
limited by a lack of randomised allocation to the treatment groups and small
samples (n=10 or 11 respectively). Only Ungvari & Vladar
(1984,
1986) treated patients with
primary delusional parasitosis.
Studies not specific for particular antipsychotics demonstrated aggregate
partial and full remission rates between 82% (n=35, not only primary
delusional parasitosis, Trabert,
1993) and 89% (n=19, only primary delusional parasitosis,
but some patients were treated with electroconvulsive therapy;
Srinivasan et al,
1994).
The only study that investigated traditional depot antipsychotics found an
aggregate response and remission rate of 93%, even in patients that could not
be treated with oral medication (Frithz,
1979).
The sample consisted only of patients with primary delusional parasitosis
(n=15). Another study using haloperidol reported a 100% response rate
(but no full remissions) (Paholpak,
1990); nine of ten patients in this study had primary delusional
parasitosis.
Across the different typical antipsychotics used, an effect of
antipsychotic medication in delusional parasitosis was noted after about
3–6 weeks (Hamann & Avnstorp,
1982; Trabert,
1995). Studies came to different conclusions as to whether or not
it is necessary to continue antipsychotics after successful acute therapy.
Symptoms of delusional parasitosis that were associated with major
depression could be treated successfully with antidepressants
(Musalek et al, 1989;
Trabert, 1993;
Bhatia et al,
2000).
One small study indicated that electroconvulsive therapy might be effective
in patients with primary delusional parasitosis
(Srinivasan et al,
1994).
A survey of British dermatologists suggested that combining
psychopharmacological and dermatological treatments (local and systemic) is
superior to single therapeutic approaches. Of particular note is that therapy
without psychotropic medication was ineffective
(Reilly & Batchelor,
1986).
We abstracted data from case series and case reports on 92 patients with
primary delusional parasitosis treated with typical antipsychoticss who met
our selection criteria – (see Table DS2 (data supplement to online
version of this paper) (Riding &
Munro, 1975; Gould &
Gragg, 1976; Munro,
1978a,b,
1982;
Frithz, 1979;
Avnstorp et al, 1980;
Ungvari, 1984;
Berrios, 1985;
Andrews et al, 1986;
Sheppard et al, 1986;
Ungvari & Vladar, 1986;
May & Terpenning, 1991;
Srinivasan et al,
1994; Chiu et al,
1996; Rasanen et al,
1997; Kim et al,
2003; Takahashi et
al, 2003).
Table 1 shows that the
majority were treated with pimozide, whereas for other typical antipsychotics
only small numbers have been reported. The majority of these patients with
primary delusional parasitosis were effectively treated with typical
antipsychotics. Pimozide was helpful for 50 of 53 patients (94%), with 24
(45%) achieving full remission. Trifluoperazine and haloperidol appeared to be
similarly effective, as did fluphenazine and flupenthixol depot.
View this table:
[in this window]
[in a new window]
|
Table 1 Summary of 92 case reports of the treatment of primary delusional
parasitosis with typical
antipsychotics1
|
Effect of atypical antipsychotics
We were able to identify only 12 case reports on atypical antipsychotics
that met our selection criteria (Table
2). Although atypical antipsychotics were effective for the
majority of patients with primary delusional parasitosis only three patients
achieved full remission. All six patients for whom risperidone was prescribed,
achieved full (four) or partial (two) remission; the dosages used ranged from
1 to 8 mg per day.
View this table:
[in this window]
[in a new window]
|
Table 2 Summary of 12 case reports of the treatment of primary delusional
parasitosis with atypical antipsychotics
|
Effect of typical v. atypical antipsychotics
The five main studies of patients with primary delusional parasitosis
treated with typical antipsychotics report very heterogeneous outcomes
(Table 3), suggesting that the
studies themselves are very heterogeneous, for example in their inclusion and
exclusion criteria (selection bias) or in their definitions of partial and
full remission (measurement bias), or that there is publication bias.
Furthermore, the eight studies of patients with secondary delusional
parasitosis treated with typical antipsychotics reported heterogeneous
outcomes. This reduces the value of comparing studies reporting the use of
typical primary antipsychotics in secondary delusional parasitosis. However,
there was a large difference between the failure rate of 5% in primary
delusional parasitosis and that of at least 26% in secondary delusional
parasitosis (
2=18.2, d.f.=2, P<0.001). It follows
that studies of secondary delusional parasitosis have nothing to contribute to
the issue of the most effective treatment for primary delusional
parasitosis.
The heterogeneity in the reported outcome of patients with primary
delusional parasitosis treated with typical antipsychotics reduces the value
of comparison with reports of atypical antipsychotics. Although the difference
is not statistically significant (
2=2.6, d.f.=2), we cannot
conclude that typical and atypical antipsychotics are equally effective
because of the innate biases already identified.

DISCUSSION
This is the first systematic review of the effectiveness of
typical and
atypical antipsychotics in the treatment of delusional
parasitosis. Our review
was based on 368 published works and
covered almost twice as many papers as
the 193 covered by the
most comprehensive review published to date
(
Trabert, 1993).
In contrast
to previous review articles (e.g.
Aw et
al, 2004;
Bourgeois &
Nguyen-Lan, 1986;
Driscoll
et al, 1993;
Freudenmann, 2002;
Lynch, 1993;
Slaughter et al,
1998;
Wykoff,
1987;
Zanol et al,
1998),
our review focuses on primary delusional parasitosis. We
separated
this important form of delusional parasitosis (delusional disorder
of somatic type) from symptomatic forms of delusional parasitosis
(`secondary
delusional parasitosis') which cover different
nosological entities and
require other forms of therapy that
focus on the underlying illness. As we
were unable to show
homogeneity in the outcomes of primary and secondary
delusional
parasitosis, we did not review other studies examining the effect
of antipsychotic medication in other types of ICD–10
F22.0 disorders,
which also differ clinically from delusional
parasitosis.
Our systematic review identified no randomised controlled trials of the
efficacy of typical and atypical antipsychotics in primary delusional
parasitosis, probably because the disorder is rare and it is difficult to
recruit patients, obtain informed consent, and achieve sufficient adherence to
medication throughout a clinical trial because of their poor insight
(Gould & Gragg, 1976;
Munro, 1982;
Ungvari & Vladar, 1986;
Freudenmann & Schönfeldt-Lecuona,
2005). It is difficult to establish a good therapeutic alliance
with these patients even in highly specialised settings
(Trabert, 1993). Because of a
lack of randomised controlled trials all our suggestions for therapy need to
be interpreted cautiously. Nevertheless we are keen to provide clinicians with
the current best evidence.
Use of typical antipsychotics
Our findings show that primary delusional parasitosis can be effectively
treated with typical antipsychotics. Outcome is generally good, although this
conclusion is limited by a possible publication bias. We confirm Trabert's
finding that the introduction of typical antipsychotics has substantially
improved remission rates (Trabert,
1995). Although the better studies have so far used pimozide
(Hamann & Avnstorp, 1982;
Ungvari & Vladar, 1984,
1986), the evidence for its
efficacy is weak by today's standards. The level of evidence for its use in
primary delusional parasitosis is IIa according to the criteria of the Agency
for Health Care Policy and Research
(1992), whereas other typical
antipsychotics such as haloperidol have only level III evidence. Pimozide
should not be used in patients with a high cardiac risk, together with other
substances that prolong the QTc interval
(Food and Drug Administration,
1996), or in elderly patients with delusional parasitosis.
Another important treatment in primary delusional parasitosis is the
intramuscular application of traditional depot antipsychotics
(Frithz, 1979), because the
main problem in clinical management is to convince patients to take oral
medication regularly. Injection may be more consistent with patients' (false)
somatic concept of their illness and require less cooperation than oral
medication. If the patient agrees to a first depot injection, the delusion may
well remit at least partially and further antipsychotic treatment will be
accepted. As the only study of this approach
(Frithz, 1979) has only 15
patients, larger samples are needed.
Use of typical antipsychotics
Our systematic review revealed only 12 usable case reports of the use of
atypical antipsychotics in primary delusional parasitosis. These provide
limited evidence that primary delusional parasitosis can be treated
effectively with these drugs. To our knowledge, this is the first complete
collection of patients with primary delusional parasitosis treated with
atypical antipsychotics, whereas many patients with secondary forms of
delusional parasitosis have been reported in recent years (e.g.
De Leon et al, 1997;
Safer et al, 1997;
Kumbier & Kornhuber, 2002;
Freudenmann, 2003;
Le & Gonski, 2003;
Scheinfeld, 2003;
Wenning et al, 2003).
Thus the evidence for the use of atypical antipsychotics in delusional
parasitosis is even weaker than for typical antipsychotics.
Most case reports are available for risperidone, whereas we are not aware
of reports on the use of clozapine, ziprasidone or aripiprazole in primary
delusional parasitosis. Amisulpride might be a good alternative given that its
selective D2/D3-antidopaminergic action resembles that
of typical antipsychotics without the same high probability of side-effects
(Freudenmann & Lepping,
2006; Lepping et al,
2006). Its lack of anticholinergic and adrenolytic effects is
particularly useful in elderly patients or patients with a higher
cardiovascular risk profile. Risperidone microspheres for intramuscular
injection provide a potentially interesting new treatment for delusional
parasitosis, as this is the only atypical antipsychotic in depot form, but
this recommendation is entirely theoretical since there are no reports of the
use of risperidone microspheres in delusional parasitosis at present.
Other treatment options
An alternative to these pharmacological strategies is electroconvulsive
therapy. The use of electroconvulsive therapy in a patient with delusional
parasitosis was first described by Harbauer in 1949 and has since occasionally
been reported (Baumer, 1951;
Bers & Conrad, 1954;
Hopkinson, 1970). Srinivasan
et al (1994) reported
effectiveness in primary delusional parasitosis in a small sample.
Electroconvulsive therapy might be a useful option in cooperative refractory
patients when antipsychotics are contraindicated or problematic (e.g. in the
elderly).
Synthesis
The very heterogeneous outcomes reported by the five main studies of
treating primary delusional parasitosis with typical antipsychotics (see
Table 3) suggest that the
studies themselves suffer from some or all of selection bias, measurement bias
and publication bias. Together with these flaws the paucity of evidence on
treating primary delusional parasitosis with atypical antipsychotics
undermines any comparison of typical and atypical antipsychotics. Despite
weaker evidence for the effectiveness of atypical antipsychotics in treating
delusional parasitosis in comparison with pimozide, the use of atypical
antipsychotics might improve side-effects, and thus adherence and patient
outcome.
It is important to strengthen this weak evidence in the future. We limited
our selection of case series and case reports of delusional parasitosis to
those including a minimum data-set for each recruited patient (age, gender,
the nature and timing of diagnosis, the name and dose of medication, and the
nature and timing of remission on a 3-point scale; Appendix 2).
Implications
Our systematic review generated weak evidence that antipsychotics are
effective in treating primary delusional parasitosis. However, in view of the
limited evidence, this recommendation is tentative and needs caution in
implementation. Since the introduction of atypical antipsychotics, pimozide is
no longer the treatment of choice for reasons of drug safety, even though it
has the best evidence of effectiveness in treating primary delusional
parasitosis. It is important to improve this evidence through rigorous,
ideally randomised, studies which compare typical antipsychotics and atypical
antipsychotics directly.

APPENDICES
Appendix 1: Aetiological classification of delusional parasitosis
(I) Primary delusional parasitosis: delusional disorder.
Primary delusion according to Berrios
(
1985), first described
by
Huber (
1957); diagnosis:
persistent delusional disorder
(ICD-10 F22.0); delusional disorder, somatic
type (DSM-IV-TR
297.1) Special form: as a shared psychotic disorder (ICD-10
F24, DSM-IV-TR 297.3)
(II) Secondary forms of delusional parasitosis: secondary to another condition.
- Concomitant psychotic symptom in another psychiatric disorder:
- Schizophrenia or other psychotic disorders; diagnosis according to
underlying psychotic disorder (ICD-10 F2x, DSM-IV-TR 295, etc).
- Major depressive disorder with psychotic symptoms or mania; diagnosis
according to underlying affective disorder (ICD-10 F3x, DSM-IV-TR 296,
etc).
- Dementia; diagnosis ICD-10 F00-03, DSM-IV-TR 290, 294.
- Delusional parasitosis based on other brain pathologies (`macroscopic')
or general medical condition:
- Brain disorders not mentioned in ICD-10 F0 (e.g. brain neoplasm/infection,
stroke); `organic damage with secondary delusions' according to Berrios
(1985), first described by
Ekbom (1938).
- Somatic illness with pruritus or paraesthesia (e.g. diabetes mellitus with
neuropathic pain, uraemia, jaundice, cancer); `paraesthesia or other somatic
pathological sensations with secondary delusions' according to Berrios
(1985); diagnosis: organic
hallucinosis or organic delusional disorder (ICD-10 F06.0 or F06.2), psychotic
disorder due to... [indicate the general medical condition] with delusions
(DSM-IV-TR 293.81) or with hallucinations (293.82) or persistent
delusional disorder (ICD-10 F22.0); delusional disorder, somatic type
(DSM-IV-TR 297.1), when delusional parasitosis is not the direct physiological
consequence of the somatic illness.
- Delusional parasitosis as a substance-induced `toxic'
psychosis:
Substance-induced `paraesthesia or other somatic pathological sensations
with secondary delusions' according to Berrios
(1985), first described by
Magnan & Saury in 1889 for cocaine addicts (`signe de
Magnan');
- Owing to psychotropic substance, e.g. cocaine, amphetamines; diagnosis:
acute intoxication, psychotic disorder, predominantly delusional (ICD-10
F1x.51) or predominantly hallucinatory (ICD-10 F1x.52); substance-induced
psychotic disorder, with hallucinations (DSM-IV-TR 292.11), with delusions
(292.12).
- Owing to non-psychotropic substances, e.g. antibiotics, steroids,
non-steroidal anti-inflammatory drugs; diagnosis: organic hallucinosis or
organic delusional disorder (ICD-10 F06.0 or F06.2), DSM-IV-TR codes see
1.
Appendix 2: Proposed minimum information required for case series and case reports of primary delusional parasitosis
Case report criteria
- Diagnosis including confirmation date
- Gender of patient
- Age of patient
- Medication used with dosage
- Outcome on 3-point scale: (0) no remission, (1) partial remission, (2) full
remission
- Length of follow-up (at least 4 weeks after date of diagnosis).

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