Annals of Indian Psychiatry

: 2019  |  Volume : 3  |  Issue : 1  |  Page : 1--3

Delusional parasitosis revisited

Neena S Sawant 
 Department of Psychiatry, Seth GSMC and KEM Hospital, Mumbai, Maharashtra, India

Correspondence Address:
Dr. Neena S Sawant
Department of Psychiatry, Seth GSMC and KEM Hospital, Parel, Mumbai - 400 012, Maharashtra

How to cite this article:
Sawant NS. Delusional parasitosis revisited.Ann Indian Psychiatry 2019;3:1-3

How to cite this URL:
Sawant NS. Delusional parasitosis revisited. Ann Indian Psychiatry [serial online] 2019 [cited 2023 Mar 25 ];3:1-3
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Delusional beliefs involving infestation with insects, parasites, and pathogens have been there since time immemorial. Georges Thibierge, a Parisian dermatologist, had described this in patients who really had scabies and were treated, and those who never had scabies but felt that they were infested. He called them “Les acarophobes” which is having fear of mites. Around the same time, Saury and Seglas reported about a similar symptom in cocaine addicts which is now referred to as cocaine bugs.[1]

In 1938, Ekbom used the German name “Dermatozoenwahn” where “derma” refers to skin, “zo” to a living being/animal, and “wahn” which means delusion. This was then later referred to as “Ekbom's syndrome.” Several researchers named it as “delusion of insect hallucination,” “delusions of infestation,” to it being finally named as “delusional parasitosis” since 1946 till today.[1],[2],[3] The syndrome was considered to be presenile or organic by Ekbom, whereas other researchers felt it to be a part of schizophrenia[4] or as a part of the affective spectrum.[5]

At present, delusional infestation (DI) is a condition which is characterized by false, firmly held beliefs of infestation, involving either living pathogens such as mites, lice, flies, fleas, ticks, and bugs and to some extent bacteria. Some patients may also claim to be infested by inanimate materials such as hair, spots or dots, pigments, sand, threads, and fibers.[5] There was also a condition called “Morgellons phenomenon” named by Leitao after doctors were unable to find the cause of her son's illness in 2002.[6] Patients usually describe various abnormal sensations of the pathogens akin to “crawling,” “biting,” “leaving marks,” “movement from one part of the body to other,” and “building nests/breeding,” etc. There still remained a controversy, whether the rigid beliefs represented only overvalued ideas or delusions. However, over time, researchers have felt that the intensity of the symptom of infestation can vary.[7]

Under the psychiatric disorders, ICD-10[8] classifies it as “persistent delusional disorder” (F-22) with at least 3 months of symptom duration, whereas the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-V)[9] diagnoses it as delusional disorder somatic type, where the core beliefs of this type are delusions around bodily functions and sensations. The most common are beliefs that one is infested with insects or parasites, that one is emitting a foul odor, that parts of the body are not functioning, that the body or parts of the body are misshapen or ugly, or the reduplication of body parts.

Freudenmann and Lepping have suggested to use the term DI as it highlights the core thought disorder and covers all kinds of imaginary pathogens by referring to the delusional theme “infestation” and not to a single species.[1] Ganner and Lorenzi were the first to describe primary and secondary forms of DI.[10]

Primary DI would be like the ICD-10 or DSM-V diagnosis of a primary delusional disorder whereas secondary would occur due to:

Schizophrenia or major depressionSubstance-induced psychosis (e.g., cocaine use)Drug-induced psychosisOrganic brain diseases such as delirium, dementia, tumors, or vascular encephalopathyGeneral medical conditions with pruritus such as renal or hepatic failure, cancer, systemic rheumatic illnesses, and diabetes.

The prevalence of primary DI or delusional parasitosis is not very well estimated, and different researchers have reported it from 8%,[2] 44%,[11] to 88%.[12] In Trabert's analysis of 449 cases, 40.3% were primary DI, and among the remaining, 21.8% had organic psychoses, 14.4% induced psychotic disorder, 10.6% schizophrenia, 9.1% affective disorders, and 3.5% neurosis.[13] DI is usually a disorder of middle-aged and elderly patients. Trabert in his meta-analysis reported the mean age of clinical presentation to be around 57.02 years.[13] The female-to-male ratio is approximately 2:1 which increases to 3:1 in elderly patients.[14] Shah et al. in their study of 40 patients[15] reported that 16 of the 40 (41%) patients had the diagnosis of delusional parasitosis, which would be primary DI, whereas among the remaining, 8 (20%) had comorbid depression, 10 (26%) had anxiety disorder, and 5 (13%) had somatoform disorder. Wong et al.[16] in their 10-year case series from a single center found that 68% of their sample had psychiatric comorbidities such as depression, anxiety, obsessive-compulsive disorder, psychosis, bipolar affective disorder, hypomania, and encopresis, whereas only 11/47 (23%) patients had primary DI.

Most common pathogens described in various studies have been insects (84%), worms (14%), bacteria (2%), and fungi (1%) which the patients always describe as too tiny to see.[1]

Several researchers have found the pathogens to be black, skin colored although any color may be present. The most frequent localizations of infestation are the skin of the hands, arms, feet, lower legs, scalp, the upper back and breast region, and the genitals.[1],[15],[17] Body orifices such as the nose, ears, mouth, anus, and the whole gastrointestinal tract have also been affected in most patients.[18],[19] Very rarely, DI of the eyes has been described in single cases.[20] Marneros et al.[21] described that their patients of primary DI reported the infestation as “in” or “under” the skin, while it was “in the body, blood, or muscle” in organic brain syndromes and “on” the skin in cases secondary to schizophrenia. Most patients also usually complain of being infested by humans, pets, plants, garden, and housing environment.

Patients have symptoms ongoing for several months and have a history of visiting several physicians and dermatologists. They try various strategies for eradicating the alleged parasites, such as repeatedly doing pest control in the house and using pesticides on themselves and even consulting entomologists to identify the parasites. In severe cases, they may even change residence several times to escape the parasites and may socially isolate themselves because of fear of contaminating others.[22] Patients frequently bring in bits of skin, lint, tissue paper, and other samples of “parasites” to try to prove the existence of these alleged parasites. These specimens are usually presented in a small bin, vessel, bag, piece of paper, or plastic foil to protect it. This clinical sign is characteristic and was first described by Perrin in 1896,[23] and this peculiar behavior was named the “matchbox sign.”[24] The assessment of these samples revealed crusts, scabs from healing skin lesions, hair, threads, and other particles from clothes, fibers, dirt, sand, and legs from flies or spiders.[1],[13],[14] In today's times, patients also get photographs or shoot video clips of the so-called pathogens. Freudenmann and Lepping have proposed the term “specimen sign,” instead of “matchbox sign” as it tells about the “pathogen” than the receptacle.[1] Several case reports have reported about this sign universally although its significance as a diagnostic sign is not well documented.[14],[22],[25] It has been seen that relatives of patients of DI may share the delusion due to their close emotional links with the person having DI. This also gets reinforced with the collecting of evidence by the patient (matchbox sign) with the relatives confirming the same as pathogens. Several case reports have described this phenomenon as folie à deux or shared paranoid disorder.[22],[25] The symptoms usually disappear when the affected are separated from the patient of DI.

Several patients create lesions on their skin to remove the pathogens, and hence, their physical examination may reveal cutaneous findings of excoriations, lichenification, prurigo nodularis, and frank ulcerations. Patients do not consider this as a psychiatric ailment and hence only visit dermatologists or other specialists for their cutaneous lesions. As a result, long duration of untreated psychosis may be a common problem in patients with DI.[26]

The management of patients with delusional parasitosis is a challenge, as patients do not believe that they have a psychiatric illness and only focus on the somatic nature of the disease. Help seeking is sought from physicians, dermatologists, or pest control companies with patients being either misdiagnosed or untreated.[1],[15] Psychiatric referral is usually taken by the dermatologist if the patient shows no improvement in the symptoms. It also depends on the liaison between the psychiatrist and the dermatologist and the awareness about the condition. Primary delusional parasitosis is a thought disorder with the conviction of being infested. Hence, it will improve on adequate treatment with antipsychotics. Sometimes, clinicians inform patients that the antipsychotic would be effective against the itch so that they consent for treatment. Lepping et al. in their meta-analysis did not find any randomized controlled trials on the effects of typical or atypical antipsychotics in either primary or other delusional parasitosis.[27]

Majority of the patients were earlier tried on oral pimozide in doses ranging between 4 and 12 mg with significant improvement, and hence, it became a drug of choice for DI. The other typical antipsychotics such as haloperidol and trifluoperazine were also tried, but data about their use in DI are comparatively less than pimozide although most of the typical antipsychotics were found to be effective. Trabert[13] had reported that the introduction of typical antipsychotics had improved the remission rates of DI. Similarly, fluphenazine and flupenthixol depot were also found effective. The level of evidence for the use of pimozide was IIa as compared to haloperidol which had Level III evidence in cases of primary delusional parasitosis.[13]

Among the atypical antipsychotics, there are several case reports citing the efficacy of risperidone and amisulpride. Not much data is available for clozapine, ziprasidone, or aripiprazole in primary delusional parasitosis. Su et al.[28] found that in 39 (44%) of their patients who received a combination of risperidone and fluoxetine, 22/39 (56%) patients showed clinical improvement. They surmised that combining an atypical antipsychotic drug and a selective serotonin reuptake inhibitor (such as fluoxetine) may work synergistically to promote the release of dopamine in prefrontal areas and thus help in the resolution of the belief. Although the combination of olanzapine and fluoxetine is available, its efficacy in primary DI has not been documented.

The use of electroconvulsive therapy in a patient with delusional parasitosis was first described by Harbauer in 1949[29] and has been used in patients. Indian data reveal its effectiveness in a small sample of patients.[30] However, electroconvulsive therapy might be considered as a useful option in patients who are refractory or intolerant to antipsychotics, etc.

The primary goal of treatment of DI should be aimed at reducing the distress caused by the thought of infestation with the pathogen and the behaviors of itching and self-cleaning associated with it. It would also require a good liaison with the dermatologist to identify these patients early and make them amenable for a psychiatric consult and treatment. Improvement in the DI would result in improvement of the associated skin lesions with reduced rates of superadded infections.

Future research directed at understanding the pathophysiology of DI and use of structural and functional MRI would probably throw more light on the alterations in the striatal dopaminergic neurotransmitter systems and help in improving the outcomes for patients of DI.


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