Delusional infestations

Chapter 18
Delusional infestations

Julio Torales

Professor of Psychiatry and Medical Psychology and Head of the Psychodermatology Unit, Department of Psychiatry, School of Medical Sciences, National University of Asunción, Paraguay


Delusional infestation (DI), sometimes known as delusion of parasitosis, is a clinical entity classified in the Koblenzer’s “strictly psychiatric skin conditions” group. It is characterized by patients’ fixed belief that their body, mainly their skin, is infested by small, vivid or non-vivid pathogens in the absence of any dermatological or microbiological evidence [1–3]. The delusion can lead to abnormal cutaneous symptoms such as itching, biting, or crawling sensations. Patients often show self-destructive behavior in an effort to rid the pathogens from under their skin, leading to excoriations, ulcerations, and serious secondary infections [3, 4]. The patients are reluctant to seek help from psychiatrists, and are likely to consult family and general physicians, dermatologists, and even microbiologists first [5]. These treatment approaches may lead to problems in the patient’s care due to difficulties in accurate diagnosis and inappropriate use of treatment programs.

In most cases, the prognosis is generally good, as long as the affected patients are adequately treated in a multidisciplinary way by dermatologists and psychiatrists with expertise in the disease [5].

This chapter presents information about how these patients may present and how psychiatrists, dermatologists, and general physicians in various settings can diagnose and manage this challenging group of patients. An illustrated case will be presented to highlight key clinical features, current diagnosis, management, and treatment of patients with DI.

Historical context

In 1938, Ekbom provided detailed description of the clinical picture, deepened its psychopathology, and called the syndrome by a German term, Dermatozoenwahn (from the ancient Greek “derma” = skin, “zoon” = living being/animal, and German “Wahn” = delusion). Because the original term was found somewhat difficult to use in different countries, the condition was called Ekbom’s syndrome. However, several authors considered this eponym ambiguous and recommended not using it, because this term is also used to refer to restless legs syndrome [1], but often the term and its use persist.

Some other terms such as dermatophobia, acarophobia, and parasiticphobia have been used, but from a psychopathological standpoint, these terms are not entirely suitable because the patient experiences are not phobia or secondary avoidance behaviors but delusions. Similarly, the term illusion of parasitosis is not correct, since the entity is not characterized by the presence of illusions, but by delusions. In 1946, Wilson and Miller introduced the term delusions of parasitosis [5–7] and it has become one of the most used and recognized names for the condition.

However, patients may report various forms of infestation, thus the name has the disadvantage of covering only one type of pathogens [1]. Therefore, the broader term delusional infestation should be preferred because it has two main advantages: It highlights the psychopathological aspect (a thought expressing delusional disorder), and it covers all varieties of imaginary pathogens by referring to the delusional theme “infestation” and not to a single species.

Strictly, DI is not a diagnosis per se and has no category of its own in the DSM-5 or ICD-10; however, it is included both in the ICD-10 and DSM-5 in the “delusional disorders” section, in the case of primary DI [8].

Case presentation

Written informed consent was obtained from the patient for publication of this case presentation. A copy of the written consent is available from the author.

Mr. A, a 48-year-old Caucasian male, divorced, a bus driver, with 2 years of history of multiple excoriations and ulcers widely distributed over his chest, back, and lower limbs (see Figure 18.1) and no previous psychiatric history, presented with his 67-year-old mother to the psychodermatology outpatient unit. He had been previously seen and assessed by a general dermatologist, who decided to refer the patient to this unit.


Figure 18.1 Multiple excoriations and ulcers widely distributed in patient’s back.

The initial dermatology assessment led to the diagnosis of DI as the patient believed that his skin injuries had been produced by “black bugs and white worms that are in his skin and eat his flesh.” He added that “these bugs and worms forced him to scratch his skin with his fingers, rocks, stones, and other elements to scrape them out of his flesh. His mother helped him in this task.” The patient’s past medical history was not significant. Dermatology assessment ruled out parasitic infestation. The patient’s mother confirmed her son’s history and she asked for help in order to cure his son. She also explained that she had been helping her son “using a little rock to scratch her son’s back.”

On evaluation in the psychodermatology unit, the patient was oriented to place and time. His sensorium was clear. His affect was euthymic and there were no other abnormal behaviours, thoughts, or delusions. At work, he was able to function normally. At the first assessment his insight and judgment were judged to be poor. All these features favored a diagnosis of DI in Mr. A. Main differential diagnosis with DI was schizophrenia, other delusional disorders, dermatitis artifacta, and excoriation (skin picking) disorder [2].

Due to the multiple excoriations and large ulcerations, treatment with colloidal solution to be applied over the cutaneous lesions was initiated in Mr. A. Also, it was decided to commence the patient on risperidone 3 mg/day in a single nocturnal dose.

After 2 weeks of treatment, the skin injuries began to heal and the delusional state of Mr. A improved and at the same time his mother’s mental state changed and she became more amenable to the idea that the condition was psychiatric. Fourteen days after starting risperidone, the patient started to question the presence of bugs and worms in his skin. After 8 weeks, there were no evidence of excoriations and ulcers in the patient’s skin (see Figure 18.2), and the delusions had disappeared. Antipsychotic treatment was continued for 6 months and the patient remained symptom-free. Mr. A. remains symptom-free at the time of this writing.


Figure 18.2 Appearance of cutaneous lesions after healing.

Clinical features

The typical patient

The typical DI patient is generally a middle-aged or elderly female with limited social contacts, generally no previous psychiatric history, and normal cognitive function [9]. DI can occur in people with any type of personality, but it is said to be more frequent in those with obsessive or paranoid characters [4, 10].

The affected body sites can include: skin, hair, various parts of the body, or natural orifices. The DI onset may be sudden or slow, and it is often accompanied by itching, which is followed by intense scratching [5, 10, 11].

When patients are able to “catch some of the pathogens,” they are taken to the physician as proof of infestation. These specimens are usually presented in a small bin, vessel, bag, piece of paper, or plastic foil to protect them. The “proof” usually consists of dull and uncritical material, such as dander, crusts, scabs from healing skin lesions, hair, threads, and other particles from clothes, fibers, dirt, or sand [12]. Increasingly patients present movies or digital photos of the sites said to be infected [1]. This peculiar behavior was named the “matchbox sign” in the Lancet

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May 29, 2017 | Posted by in PSYCHIATRY | Comments Off on Delusional infestations
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