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Year : 2013  |  Volume : 58  |  Issue : 1  |  Page : 49-52
Delusions of parasitosis

1 School of Medicine, University of Utah, Salt Lake City, UT; Department of Dermatology, University of California San Francisco, CA, USA
2 Department of Dermatology, University of California San Francisco, CA, USA

Date of Web Publication31-Dec-2012

Correspondence Address:
Jillian W Wong
UCSF Psoriasis and Skin Treatment Center, 515 Spruce Street, San Francisco, CA 94118
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0019-5154.105309

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Patients with delusions of parasitosis (DOP) are more commonly recognized in dermatology practices today. However, dermatologists may feel uncomfortable treating these patients because of the psychiatric nature of their disorder. As a result of the fact that DOP patients strongly prefer to seek treatment from dermatologists rather than mental health professionals, it is important for dermatologists to be well equipped with a basic understanding of the disorder and with tools to assist this patient population. In this review, we discuss the epidemiology, presentation, differential diagnosis and treatment strategy for patients with DOP.

Keywords: Delusions of parasitosis, delusional infestation, Morgellons

How to cite this article:
Wong JW, Koo JY. Delusions of parasitosis. Indian J Dermatol 2013;58:49-52

How to cite this URL:
Wong JW, Koo JY. Delusions of parasitosis. Indian J Dermatol [serial online] 2013 [cited 2023 Nov 29];58:49-52. Available from:

   Introduction Top

Delusions of parasitosis (DOP), also known as "delusional infestations," "acarophobia," "Ekbom syndrome" and "Morgellons," is classified as a primary psychiatric disorder. The pathology of primary psychiatric disorders, including DOP, is psychological. This means that the patient has no primary skin pathology, and all skin findings are secondary to skin manipulation by the patient.

Psychosis is defined by the presence of a delusion. The most common type of psychotic patient that dermatologists treat has monosymptomatic hypochondriacal psychosis (MHP). MHP is characterized by a delusional ideation that focuses on one hypochondriacal concern. [1],[2],[3] DOP is the most common type of MHP seen by dermatologists. In fact, up to 90% of patients with this condition are seen by dermatologists. [4] Except for the presence of an "encapsulated" delusional ideation, patients with MHP usually appear appropriate in other capacities. It is often the case that MHP patients have hallucinatory experiences compatible with their specific delusion. For example, for patients with DOP, many experience formication, which is manifested as cutaneous sensations of crawling, biting and stinging. In addition, DOP patients experience a significant decline in quality of life, including decreased work productivity or job loss, disability and social isolation. [5]

As a result of the high percentage of DOP patients seeking help from dermatologists, it is important for those in our profession to be equipped with the expertise needed to accurately identify and treat this special patient population. In this concise review, we will cover the epidemiology, presentation, differential diagnosis and treatment strategies for patients with DOP.

   Materials and Methods Top

We conducted a search of PubMed's Medline database of articles. Articles containing the key terms delusions of parasitosis, delusional infestation and review were reviewed. The search was limited to articles in English. A total of 26 articles spanning from 1935 to 2012 were included in this review.

   Results Top


Based on a review of the medical literature, the prototypical patient with DOP is an older woman. The female to male ratio is 2:1, showing a predominance in female patients. However, among younger patients, the female to male ratio is 1:1 and for those older than 50 years of age, it is 3:1. [6] Reports demonstrate that the average age of onset of DOP is 55.6 years in one study and 65 years in another study. [7],[8] In addition to older female patients, DOP is frequently observed in younger male and female patients in their 20 s or 30 s, often of lower socioeconomic status and marginal societal adaptation. Therefore, there appears to be a bimodal distribution of DOP patients, with a peak at the 20-30 years age group and an even larger peak at 50 years of age and older.


DOP patients have a fixed, false belief that they are infested with parasites or other organisms. They usually report skin lesions, excretion of fibers or solid material from the skin and, typically, cutaneous sensations of formication (crawling, stinging and/or biting) with or without pruritus, and, at times, "pins and needles" that can be chronic and recurrent. [9],[10] There are also patients who provide descriptive, complex life cycles in exquisite detail for these "parasites," describing how they can breed and multiply. One other notable feature is that in approximately 5-15% of DOP cases, delusions are shared with friends or relatives, known as folie à deux. [11]

Patients with DOP often present with a preoccupation with fibers or other inanimate objects, claiming that they "move" and hence are "alive." Moreover, they may bring into the clinic small remnants of skin debris, tissue paper, hair and filaments in an attempt to demonstrate that the "parasites" exist. [10],[12] A recent descriptive study conducted by the Centers for Disease Control of 115 Kaiser Permanente Northern California patients in the US between 2006 and 2008 collected detailed epidemiologic data, performed clinical evaluations and analyzed materials collected from patients' skin for patients reporting fibers, specks, dots, threads, granules, fuzzballs and other forms of solid material coming out of the skin. [13] These patients also experienced disturbing skin symptoms of pruritus, crawling, stinging, biting or a pins and needles sensation and/or had skin lesions such as a rash, ulcer, nodule or wound. The study found no difference in the sociodemographic, clinical or histopathologic characteristics of the patients who did and did not report fibers. The fibers that were collected from the patients' skin were skin fragments and fabric material. In addition, solar elastosis was the most common histopathologic abnormality in the biopsies taken. There were no mycobacteria or parasites detected in this study population. [13] The main conclusion of the study, not surprisingly, is that this condition appears to represent a psychiatric disorder.

Differential diagnosis

It is important to consider the differential diagnosis for patients who present with DOP-like symptoms; not every patient complaining of an infestation without physical evidence of infestation has DOP. The first differential diagnosis to consider is formication. [14] Patients with formication experience crawling, biting and stinging sensations of the skin. However, unlike DOP patients, those with formication have no firm belief that their symptoms are due to a parasite or infestation. Some patients explicitly state that they do not believe the sensations are due to a living thing, while other patients have considered an infestation as a possible cause for the symptoms but are not convinced that this is the case. By definition, when patients are not certain whether they have an infestation or if they believe they do not have an infestation, these patients are not psychotic as they do not have a fixed and absolute delusional ideation. Formication by itself can still warrant the use of drug therapy because it can be debilitating. Formication may be idiopathic or secondary to an underlying neurological diagnosis such as multiple sclerosis. For the treatment of DOP, an antipsychotic medication, pimozide, generally works well even if they do not have a delusional ideation. [14] The author (JK) has observed that many of these initially non-delusional patients with formication gradually become more and more delusional over time until they eventually become fully delusional with fixed, non-negotiable convictions about having an infestation.

The second differential diagnosis for cases resembling DOP is formication and delusions secondary to substance abuse. Drugs such as cocaine and amphetamines can induce formication and, at times, a delusional state that may be similar to idiopathic DOP. [6] In fact, cocaine users have labeled the phenomenon of formication induced by cocaine as "cocaine bugs." Although most cocaine abusers know they do not have real infestations, but rather they are experiencing a hallucination induced by their drug use, some chronic cocaine users can rarely develop the delusion that they are being infested. The main treatment for drug-induced sensations similar to DOP is detoxification.

A third differential diagnosis for idiopathic DOP is as a manifestation of a global psychiatric derangement. [15] Some schizophrenia patients may have a delusion that they are being attacked by "organisms" as a result of paranoia. Patients with a subtype of severe depression, called psychotic depression, may believe they are contaminated or are dirty because of an infestation with mites. These patients also present, however, with prominent depressive symptoms such as depressed mood, hopelessness, helplessness, excessive guilt and worthlessness. These cases should be treated based on the underlying diagnosis. For psychotic depression, simultaneous use of an antipsychotic and an antidepressant may be warranted.

The fourth differential diagnosis that may be considered for DOP is a true skin disorder where the diagnosis was missed. Patients with Grover's disease and scabies incognito have been misdiagnosed for DOP. Grover's disease may present with similar sensations to DOP because the primary lesions of the disease are small and pruritic, and the patient may often have excoriated all the lesions before being evaluated by the dermatologist. In both cases, it is important to conduct a careful physical evaluation and attempt to locate a primary lesion. DOP associated with Grover's disease may respond to treatment with isotretinoin. [14]

Other diagnoses that may be considered are of systemic causes. Nutritional deficiencies can present with DOP-like symptoms, and include pellagra, Vitamin B12 deficiency and folate deficiency. [7],[16],[17],[18] DOP-like symptoms can present in the setting of cerebrovascular disease and central nervous system disorders such as dementia, multiple sclerosis, head injury and multiple system atrophy. [7],[16],[19],[20],[21],[22] Central nervous system infections such as neurosyphilis, meningitis and encephalitis have also been associated with DOP-like symptoms. [7] Appropriate laboratory tests may be considered in evaluating delusional patients for possible underlying medical causes.


Ideally, because of the psychiatric nature of the disorder, patients with DOP should be treated by two professionals - a dermatologist as well as a psychiatrist. Generally, however, these patients refuse to see a mental health professional because they do not recognize that the underlying cause of their symptoms is of a psychiatric nature. Therefore, dermatologists need to know how to effectively treat DOP patients without the assistance of a mental health professional or else a large proportion of these patients will never be effectively treated. [23]

The first and most critical step toward assisting these patients effectively is taking the time to develop a strong physician-patient therapeutic alliance. [24] Without a strong alliance, DOP patients are unlikely to be compliant in taking antipsychotic medications. This may include performing laboratory tests, cultures or examining patient specimen samples.

Historically, the pharmacologic treatment of choice for DOP is an antipsychotic medication called pimozide (Orap ® ). [25],[26] Non-pharmacologic interventions have limited use for DOP patients because the underlying disorder is psychosis. By definition, psychotic patients cannot be talked out of a delusion, or else they would not have a delusional disorder in the first place. Pimozide can be prescribed with a starting dose of as low as half a tablet or 0.5 mg daily. As there is a possibility of extrapyramidal side-effects, including restlessness and stiffness, the starting dose of pimozide should be low. These side-effects can generally be controlled with diphenhydramine (Benadryl ® ) 25-50 mg every 4-6 h as needed or benztropine (Cogentin ® ) 1-2 mg four times daily as needed. The dosage can be gradually increased until the optimal response is obtained. It can be increased by as little as half a tablet or 0.5 mg increments as slowly as on a biweekly basis. Clinical improvement is typically evident when the patient reaches the dose of 3-5 mg of pimozide daily. Before starting pimozide, the clinician should consider checking an electrocardiogram (ECG) to ensure the patient does not have an arrhythmia or increased QT interval. Even for those patients without a history of cardiac conduction abnormalities, it may still be advisable to obtain pre-treatment ECG.

Once the optimal dosage of pimozide is found, it should be maintained for 1-3 months. During this period, if the patient continues to show improvement, whereby the formication becomes minimal or non-existent, the dosage can then be gradually decreased by 1 mg every 2-4 weeks to see whether the patient can be tapered off the pimozide. Once pimozide is discontinued, patients often feel that the pimozide destroyed the organisms or that the organisms are no longer causing bothersome symptoms. Except in a very rare occasion, the patient remains convinced that he or she did have an infestation. Even though these patients almost never actually change their mind, a successful treatment with pimozide typically results in a good outcome, whereby the patient's continued belief that he or she did have an infestation no longer matters as the patient is now convinced that the organism has been destroyed. The risk of tardive dyskinesia exists, but the actual occurrence is very rare due to low dosage and short-term use.

If extrapyramidal side-effects occur, and do not resolve with benztropine or diphenhydramine, patients may be switched to atypical antipsychotics such as risperidone (Risperdal ® ), olanzapine (Zyprexa ® ), quetiapine (Seroquel ® ), ziprasidone (Geodon ® ) and aripiprazole (Abilify ® ). Prior to starting these medications, it is crucial to check a complete blood count (CBC) at baseline, 1 month, 6 months and 1 year in order to monitor for bone marrow suppression. Following this timetable, patients should also have fasting lipids, fasting glucose, glycated hemoglobin (HBA1C), weight and body mass index monitored for possible metabolic complications such as hyperlipidemia, hyperglycemia and excessive weight gain.

Risperidone (Risperdal ® ) is the preferred alternative to pimozide for DOP. [27] It is often initiated at 0.5 mg at night, as it can be sedating. Then, the medication can be up-titrated by 0.5 mg increments every 2-4 weeks to a therapeutic range, or approximately 1-3 mg each night. While on the medication, it is important to regularly monitor for elevated prolactin levels, which can lead to galactorrhea, increased risk of fractures, low bone mineral density and sexual dysfunction.

The second preferred option is olanzapine (Zyprexa ® ). [27] Olanzapine can be started at 2.5 mg daily, and slowly titrated to a therapeutic dose of 5-10 mg daily. Patients can develop metabolic syndrome and, therefore, should be monitored regularly for weight gain, HbA1C, fasting glucose and fasting lipids.

Many cases have reported that quetiapine (Seroquel ® ) is effective for DOP. [27] It may be initiated at low doses of 12.5 mg in the evening, and slowly titrated up to 200 mg each night. It is often sedating, but this side-effect is fleeting and typically resolves after 3-7 days. Finally, it is important to monitor for orthostatic hypotension while taking quetiapine.

Case reports have also shown the effectiveness of ziprasidone (Geodon ® ) in DOP. [27] It can be started at 5-10 mg twice daily, and slowly titrated up to a therapeutic dose of 20-50 mg twice daily. It is often recommended that ziprasidone be taken with meals as it has lipid-absorptive properties. Anxiety and restlessness have been reported after taking this medication.

Aripiprazole (Abilify ® ) has been shown to be effective in DOP through case reports. [27] It can be started at 2-5 mg daily, and slowly titrated to a therapeutic dose of 10-15 mg daily. As it can be a stimulant, aripiprazole is typically taken during the morning. It is important to monitor for weight gain as well as the side-effects of restlessness, anxiety, weakness and headache.

   Conclusion Top

DOP patients are commonly seen in dermatology practices. However, dermatologists may feel uncomfortable treating these patients because of the psychiatric nature of the disorder. In managing patients with DOP, clinicians should be well equipped with a basic understanding of the presentation, epidemiology, differential diagnosis and treatment for these patients. The most important way to approach a DOP patient is by building a strong therapeutic alliance so that effective pharmacotherapy in a setting of trust and support can be executed.

   References Top

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8.Wilson JW, Miller HE. Delusion of parasitosis (acarophobia). Arch Derm Syphilol 1946;54:39-56.  Back to cited text no. 8
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20.Blasco-Fontecilla H, Bragado Jiménez MD, García Santos LM, Barjau Romero JM. Delusional disorder with delusions of parasitosis and jealousy after stroke: Treatment with quetiapine and sertraline. J Clin Psycho pharmacol 2005;25:615-7.  Back to cited text no. 20
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