Table of Content


Spring 2020, Vol. 28 No. 1

Hong Kong J. Dermatol. Venereol. (2020) 28, 17-18

Views and Practice

Tips on managing delusion of parasitosis from a psychocutaneous clinic

YC Giam and KL Chan


Delusions of parasitosis (DoP) is defined as a form of mono-symptomatic hypochondriacal delusional disorder of infestation of the body. Patients present to the dermatologist with a fixed false belief of infestations of the body, and then carry out ritualistic behaviour to get rid of their infestations. Although the pathophysiology is unclear, it is likely to be multifactorial and include social vulnerability,1 genetics, organic factors, premorbid traits, acute triggers.2,3

The main challenge is therapy, as the patients do not have insight to their problem and are often otherwise normal. The mainstay of treatment is antipsychotics, and the addition of antidepressants. In our experience, we use the novel combination of risperidone and fluoxetine. Delusions of parasitosis is uncommon but to date we have seen about 90 cases in the ten years in our psychocutaneous clinic since 2004.

Clinical presentation

Chinese form the majority of patients, about 87%, in our multiracial country, of which 57% were females, 41% were males.4 Most presented with stories like a hundreds of insects buzzing over their heads, inside their skin, and thus multiple excoriations are seen. Attempts to rid the insects included using detergents, antiseptics, scabicides, kerosene, self-fumigation with smoke from wood, or calling in the environmental agencies to fumigate their homes. A number of their neighbours moved away as patients have poured kerosene on their lobbies to rid the insects.


As counselling does not work, we prescribe antipsychotic medication, risperidone and combined with a selective serotonin reuptake fluoxetine.5-7

Pimozide is not available locally, due to its adverse extrapyramidal side effects, including tardive dyskinesia which may be irreversible.3 It may also prolong the QT interval, which limits its use.8 Olazepine is used occasionally. Previous studies have suggested that combining an atypical antipsychotic drug and inhibitor (such as fluoxetine) work synergistically to promote the release of dopamine in prefrontal areas.7,9 Animal studies have shown that the co-administration of risperidone and fluoxetine increased the extracellular level of cortical dopamine, serotonin and noradrenaline.10

The dose of risperidone is started low at 0.5 mg and titrated upwards till 1 mg. One should be wary of side effects such as extra pyramidal signs, which can be subtle. Fluoxetine is started at 20 mg daily. As patients are aware that these are antipsychotic drugs, we say that "drugs have many functions and these will help them rid the insects."

It takes about two to three months to improve, and often patients need to be maintained on a reduced dose. A number of patients relapse when the medication is stopped. More studies may need to be conducted to find the medication with optimum efficacy.

The management is challenging and much of this difficulty lies in building a trusting relationship with the patient. Physicians need to learn how to cope with psychiatric patients by displaying active listening skills and showing interest and empathy in their concerns. However, in the case of delusion of parasitosis, it is important not to collude with the patient and offer them hope in dealing with their problem.


1. Freudenmann RW, Lepping P. Delusional infestation. Clin Microbiol Rev 2009;22:690-732.

2. Lepping P, Russell I, Freudenmann RW. Antipsychotic treatment of primary delusional parasitosis: systematic review. Br J Psychiatry 2007;191:198-205.

3. Lepping P, Freudenmann RW. Delusional parasitosis: a new pathway for diagnosis and treatment. Clin Exp Dermatol 2008;33:113-7.

4. Su P, Teo WL, Pan JY, Chan KL, Tey HL, Giam YC. Delusion of Parasitosis: A Descriptive Analysis of 88 Patients at a Tertiary Skin Centre. Ann Acad Med Singapore 2018;47:266-8.

5. Freudenmann RW, Lepping P. Second-generation antipsychotics in primary and secondary delusional parasitosis: outcome and efficacy. J Clin Psychopharmacol 2008;28:500-8.

6. Ahmad K, Ramsay B. Delusional parasitosis: lessons learnt. Acta Derm Venereol 2009;89:165-8.

7. Kulkarni K, Arasappa R, Prasad MK, Zutshi A, Chand PK, Murthy P, et al. Risperidone versus olanzapine in the acute treatment of persistent delusional disorder: a retrospective analysis. Psychiatry Res 2017;253:270-3.

8. Elmer KB, George RM, Peterson K. Therapeutic update: use of risperidone for the treatment of monosymptomatic hypochondriacal psychosis. J Am Acad Dermatol 2000;43:683-6.

9. Quintin P, Thomas P. Efficacy of atypical antipsychotics in depressive syndromes. Encephale 2004;30:583-9.

10. Kamiñska K, Golembiowska K, Rogóż Z. Effect of risperidone on the fluoxetine-induced changes in extracellular dopamine, serotonin and noradrenaline in the rat frontal cortex. Pharmacol Rep 2013;65:1144-51.