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types of antipsychotics used in the treatment
of DP. A systematic review was not
completed to allow for discussion of clinical
application of treatment.
Results: Risperidone and olanzapine are
currently the most commonly used atypical
antipsychotics in DP treatment and are
as efficacious as pimozide (full or partial
remission rates of 68% and 90% respectively
vs. pimozide average of 79%), and have
fewer side effects. Other atypicals such as
quetiapine, aripiprazole and paliperidone
as well as risperidone long acting injections
have demonstrated promising remission
rates > 75% in a limited number of patients,
but still require further studies to be
considered first-line therapies.
Conclusion: Limited clinical studies
with small study populations implicate
risperidone and olanzapine as first line
treatments, but more randomized control
trials are needed. We also review methods
of how dermatologists may best initiate
treatment with atypical antipsychotics.
Keywords: Delusional parasitosis, atypical
antipsychotics, typical antipsychotics,
treatment
INTRODUCTION
Delusional parasitosis is a
monosymptomatic hypochondrial psychosis
characterized by an unwavering false
belief that one is infected with parasites. 1
Thieberge first described this disorder in
1894, and the name delusional parasitosis
(DP) was introduced in 1946. 2 The
prevalence of DP is not well established,
but is considered rare. Overall, the femaleto-male
ratio of affected individuals is
approximately 2:1, with the mean age of
diagnosis being slightly higher for females
than males (mean age, 50 years to 40 years). 3
The classification of DP is as either primary
or secondary. Primary DP is characterized
by a somatic delusion lasting for at least
1 month, whereby patients do not meet
criterion A for schizophrenia and there can
be no underlying cause of the delusion. 4
Secondary DP results from the use of a
substance, organic causes, or other medical
or psychiatric disorders with the most
common causes being schizophrenia,
diabetes, depression, cardiovascular
events, and neurodegenerative disease. A
comprehensive review of other secondary
causes of DP is discussed by Huber et al.
(2007). 5
Given that DP is a somatic delusion, patients
often initially present to dermatologists
instead of psychiatrists with symptoms of
pruritis, crawling sensations attributed to the
presence of parasites under the skin leading
to secondary excoriations, lichenification,
prurigo nodularis and full thickness
ulcers. 6, 7 Commonly, patients bring in
samples of skin in small boxes as proof
that the parasites exist; this stereotypical
presentation is referred to as “the matchbox
sign.” 8 Furthermore, patients may attempt
to rid these “parasites” with anti-scabetic
permethrin cream or even perform harmful
skin cleansing rituals with disinfectants
or pesticides. 9
METHODS
Treatment of DP requires the differentiation
between the primary and secondary forms.
Treatment of secondary DP relies on treating
the underlying cause or cessation of the
offending drug. 10 Treatment of primary DP
has mostly revolved around typical and the
newer atypical antipsychotics, which have
differing mechanisms of action compared
to typical antipsychotics. We conducted a
literature search using combinations of the
search terms: delusion*, parasitosis, typical,
atypical, antipsychotics and treatment, in
EMBASE and PubMed inclusive of studies
published prior to May 1, 2010. For studies
involving typical antipsychotics, only those
with n≥20 (including placebo group) were
reviewed, since these represent the most
influential studies on which the basis of
typical antipsychotic treatment is formed.
Due to the relatively recent introduction
of atypical antipsychotics in the treatment
of DP, the n values for these studies were
significantly smaller; thus sample size was
not used as a definitive exclusion criterion.
We included at least one study for each
atypical. The criteria we considered included
the size of the study, with preference being
given to larger sample sizes; whether or
not numerous atypicals were compared
within the same study, to control for variable
treatment practices; and how well the
study represented the general treatment
population with respect to disease severity,
co-morbidities and age.
RESULTS
Typical antipsychotics
The most common typical antipsychotic
used in the treatment of DP is pimozide. 11
Pimozide is an approved treatment for
Gilles de la Tourette syndrome in the United
States, but it has also been shown to have
a therapeutic effect for numerous offlabel
disorders, such as DP. 10-19 Pimozide’s
primary mechanism of action is via central
Dopamine-receptor D2 antagonism. 12 One
advantage of pimozide over other typical
antipsychotics is its weak noradrenergic
receptor blockade effect which reduces
adverse side effects such as orthostatic
hypotension and dizziness. 14
A number of case reports, case series, and
double-blind crossover trials showing
the effects of pimozide in DP have been
conducted (summarized in Table 1) 15-19 .
The first double-blind crossover study was
performed by Hamann and Avnstorp (1982)
which demonstrated that 10 out of 11 DP
patients had a decrease in Brief Psychiatric
Rating Scale points and improvement of
delusion and itching following 6 weeks
of treatment with pimozide, while only
one patient from the placebo group
experienced improvement in the 4 week
evaluation period. 15 In 1986, another
double-blind crossover study showed
significant improvement in 10 DP patients
administered 2-8 mg/day of pimozide for
3 weeks followed by a relapse following 2
weeks of placebo treatment and subsequent
improvement when pimozide was restarted.
Improvement was based on the authors’
own rating scale using symptoms of DP. 13
Although these studies used a placebo
control, the results are limited by the
small sample size (i.e. n=11 and n=10
13, 15
respectively).
The rates of partial and full remission are
variable amongst studies with pimozide.
Zomer et al. (1998) found a partial to full
remission rate of 61% (11 out of 18 patients)
in patients treated with pimozide compared
to 20% (3 out of 15) in the non-treatment
group. 16 A survey conducted by Lyell (1983)
demonstrated 44 of 66 patients treated
with pimozide demonstrated full or partial
remission (combined remission rate of
67%). 17 Partial and full remission of DP in
patients treated with pimozide have been
reported as high as 87% (n = 46)18 to 100%
(n=10). 13
The long-term efficacy of treatment with
pimozide was demonstrated in a follow-up
study by Lindskov and Baadsgaard (1985). 19
Fourteen patients were followed up between
19 and 48 months after termination of
pimozide treatment. Seven patients had
improved, while 4 had deterioration of
their symptoms and 3 had relapses that
responded well to intermittent pimozide
treatment.
A systematic review conducted by Lepping
et al. (2007) found a total of 92 patients
treated with typical antipsychotics for
primary DP. Of those 92, 40 (43%)
had partial remission, 45 (49%) had
full remission and 7 (8%) showed no
improvement or were lost to follow-up. 10 Of
the 53 patients treated with pimozide, 50
had either full or partial remission (94%),
University of Alberta Health Sciences Journal • April 2012 • Volume 7 • Issue 1 9
REVIEW