Sanju George 1 , Esther Alleyne 2 and *Sarabjeet Kohli 3 .

1 Consultant Psychiatrist, Birmingham & Solihull mental health foundation Trust

2 Student Doctor, University of Birmingham,

3 Specialty Registrar, Birmingham & Solihull Mental Health foundation Trust,



First described by the French dermatologist Thibierge in 1894 (1) (termed acarophobie), this syndrome (delusional parasitosis) has had various names since (see below). Considerable nosological ambiguity has surrounded this concept through its evolution but the current psychiatric classificatory systems (ICD-10 & DSM-IV) conceptualise it as a delusional disorder – wherein the person holds a firm, unshakeable belief (delusion) that there are parasites or insects infesting his/her skin. It is an uncommon psychiatric syndrome but one that often runs a chronic and debilitating course. Patients with delusional parasitosis (DP) more often present to dermatologists and are reluctant to accept a psychiatric referral: hence pose a challenge in timely diagnosis and treatment. In this brief overview, we will discuss the clinical features, diagnostic considerations and treatment options of this condition.

Different terminologies for DP

• Acarophobie (Thiebierge, 1894) (1)
• Entomophobia (Pierce, 1921) (2)
• Praseniler Dermatozoenwahn (Ekbom, 1938) (3)
• Delusions of parasitosis (Wilson & Miller, 1946) (4)
• Ekbom syndrome (Petho & Szilagyi, 1970) (5)
• Delusions of infestation (Hopkinson, 1970) (6)
• Monosymptomatic hypochondriacal psychosis (Munro, 1980) (7)



DP is an uncommon psychiatric disorder and no precise estimates of its prevalence are available in psychiatric literature: case reports and case series predominate. DP is most often seen in middle-aged women (age range of 45 to 55 years), with a female to male ratio of 2:1 to 3:1 in those aged over 50 (8) and a ratio of 1:1 in the under 50s. Some have noted a bimodal peak in age distribution: 20 to 30 years and over 50 (9). It has an insidious onset and runs a chronic course, with considerable time delay (often many years) before patients’ first presentation for treatment. However, Trabert (10) in a meta-analysis of 1,223 cases of DP found the course to be not always chronic – i.e. full remission in 50% of cases.

Clinical features

The pathognomonic symptom is the false, unshakeable belief (delusion) that parasites infest the skin. Delusions often tend to be chronic – a mean duration of 3+/- 4.6years was noted in an analysis of 363 cases of DP (10). Patients often present to dermatologists or GPs with symptoms of itching and excoriations on their skin, attributing it to infestation by parasites or other organisms (See box II for a list of organisms described in patient accounts of DP). They might also report feeling and even seeing the parasites and some go on to describe their colour, shape, etc. Some case reports in literature (11) even present patient drawings of the parasites. Patients could have superficial excoriations, old scars or even deeper wounds, all a result of attempts to rid themselves of the parasites. Although the arms, forearms and trunk are the most commonly affected areas, scalp, fingernails, ears, nose, eyes and genitalia all have been reported to be infested. On occasions, they collect skin peelings, dried pus, dried blood and other debris in match boxes – as “evidence” of parasitic infestation. This is called the “match box sign.” (12). In an attempt to eradicate the organisms, patients resort to measures such as using insecticides, pesticides or bleach, shaving the area and so on.

Types of insects described in DP

• Bugs
• Insects
• Worms
• Mites
• Lice
• Larvae
• Flea
• Ants
• Spiders
• More than one

DP usually runs a chronic course, although in nearly 50% of cases achieve remission. Patients with a shorter duration of delusion at initial presentation have been found to have a better outcome. Psychopharmacological interventions have been found to considerably improve the outcome of this disorder.

It is interesting to note that in 5% to 15% of cases of DP, the delusional belief is shared by the spouse, relative or friend (13) – such a shared delusional disorder is called folie a deux. In such cases there is usually a very close relationship between the primary case (‘inducer’) and the secondary case (‘induced’), and full remission occurs in most cases in the ‘induced’ after separation from the ‘inducer’.


Key points in assessment

• Express empathy and use a non-confrontational approach to the symptom/delusion
• Establish the presence of a delusion of infestation
• Assess its impact on day-to-day functioning
• Explore the patient’s disease model
• Rule out organic, schizophrenic and affective aetiology
• Assess mood and risk of DSH
• If diagnosis is suspected, refer to psychiatrist for further management

A thorough assessment and diagnostic confirmation are essential prior to initiating treatment for DP. Please bullet point list above for the key issues to bear in mind while assessing a patient with suspected DP. If the patient has not had a dermatological assessment, it might be prudent to arrange this with a view to ruling out real parasitic infestation.


ICD –10 diagnostic criteria for DP
• The delusion is the only or the most conspicuous clinical characteristic
• Must be present for at least 3 months
• Must not be secondary to organic, schizophrenic or affective disorders

The key diagnostic feature is the presence of a delusion of infestation that is not secondary to organic or psychiatric causes (see ICD-10 diagnostic criteria in Box IV). It is crucial to rule out other etiological possibilities before a diagnosis of DP is confirmed (see Box V for a list of differential diagnosis).

Differential diagnoses in DP

• Skin conditions – scabies, Grover’s disease
• Primary psychiatric disorders – schizophrenia, psychotic depression
• Psychoactive substance misuse – cocaine (‘cocaine bugs’, amphetamines
• Endocrine disorders – hypothyroidism, diabetes mellitus
• Organic conditions – dementia, B12 deficiency, pellagra, multiple sclerosis, neurosyphilis, renal failure, leprosy


A major obstacle in treating these patients (especially those presenting to dermatologists or GPs) is getting them to accept a psychiatric referral. Patients who insist on a dermatological causation for their DP, often fail to comply with antipsychotic medication. Where possible, any treatment plan is best co-ordinated and delivered in a psychiatric-dermatologic liaison setting.

Given these patients’ reluctance to accept a psychiatric assessment, it is crucial that the psychiatrist establishes a good rapport and trusting relationship. Acknowledge the patient’s symptoms but do not collude with the delusional belief or out rightly challenge the delusion. Pharmacotherapy is the mainstay of treatment of DP: both conventional antipsychotics and newer atypical antipsychotics have been found to be effective in treating this delusional disorder. Most early research in this field suggests Pimozide as the treatment of choice (14,15,16). However, in view of pimozide’s unfavourable side effect profile (extrapyramidal, anticholinergic and cardiac) more recent studies have used newer antipsychotics such as olanzapine (17), queitiapine (18) and risperidone (18,19). To date, there have not been studies comparing pimozide with newer antipsychotics. Some patients treated with antipsychotics can successfully come off it after symptom remission but in other cases treatment often tends to be long-term. Apart from treating the delusion, co-existing depressive syndromes should be treated with antidepressants. Other treatments tried for DP, with limited effectiveness, include supportive psychotherapy and electroconvulsive therapy.


Initial presentations of DP are more often in dermatologic practice and a major obstacle in its management is getting patients to accept a psychiatric referral and treatment. Prompt diagnosis and treatment can help prevent chronicity and considerable morbidity. It is best to manage this condition in a psychiatric – dermatologic liaison setting.



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2. Pierce DW. Entomophobia. Bull Southern Calif Acad Sci 1944; 43:78-80.

3. Ekbom KA. Der prasenile Dermatozoewahn. Acta Psychiatr Neurol 1938; 13:227-259.

4. Wilson JW, Miller HE. Delusion of parasitosis. Arch Dermatol Syphilol, 1946; 54:39-56.

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6. Hopkinson G. The psychiatric syndrome of infestation. Psychiatr Clin, 1973; 6:330-45.

7. Munro A. Monosymtomatic hypochondriacal psychosis manifesting as delusions of parasitosis. Arch Dermatol, 1978; 114:940-3.

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11. Zanol K, Slaughter J, Hall R. An approach to the treatment of psychogenic parasitosis. Pharmacol and Therap 1998; 37:56-63.

12. Zomer SF, De Wit RFE, Van Bronswijk JEHM, Nabarro G, Van Vloten WA. Delusions of parasitosis. A psychiatric disorder treated by dermatologists? An analysis of 33 patients. Br J of Dermat, 1998; 138:1030-2.

13. Trabert W. Shared psychotic disorder in delusional parasitosis. Psychopathology, 1999; 32:30-34.
14. Reily TM. Pimozide in monosymptomatic psychosis. Lancet, 1975; 1:1385-6.

15. Hamman K, Avnstorp C. Delusions of infestation treated by pimozide: a double blind crossover clinical study. Acta Dermato-Venerologica, 1982; 62:55-8.

16. Bhatia M, Jagawat T, Choudhary S. Delusional parasitosis: A clinical profile. Intl J Psychiatry Med, 2000; 30:83-91.

17. Meehan WJ, Badreshia S, Mackley CL. Successful treatment of delusions of parasitosis with olanzapine. Arch Dermatol, 2006; 142:352-5.

18. Wenning MT, Davy LE, Catalano G, Catalano MC. Atypical antipsychotics in the treatment of delusional parasitosis. Ann of Gen Psychiatr, 2003; 15:3-4.

19. Elmer MKB, George MRM, Peterson MK. Therapeutic update: Use of risperidone for the treatment of monosymptomatic hypochondriacal psychosis. J Am Acad Dermatol, 2000; 43:683-6.

Declaration of interests: None


Copyright Priory Lodge Education Ltd. 2013 -

Firs Published January 2013

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