eMedicine Specialties > Dermatology > Psychocutaneous Diseases

Delusions of Parasitosis

Author: Noah S Scheinfeld, MD, JD, FAAD, Assistant Clinical Professor, Department of Dermatology, Columbia University; Consulting Staff, Department of Dermatology, St Luke's Roosevelt Hospital Center, Beth Israel Medical Center, New York Eye and Ear Infirmary; Private Practice
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Updated: Jan 7, 2010

Introduction

Background

Delusions of parasitosis manifest in the patient's firm belief that he or she has pruritus due to an infestation with insects. Patients may present with clothing lint, pieces of skin, or other debris contained in plastic wrap, on adhesive tape, or in matchboxes. They typically state that these contain the parasites; however, these collections have no insects or parasites. This presentation is called the matchbox sign, or what the authors term the "Saran-wrap sign."

The patients have no obvious cognitive impairment, and abnormal organic factors are absent. True infestations and primary systemic diseases that cause pruritus are not involved. Primary skin lesions are not present. Physical examination may reveal no lesions, but only linear erosions with crusts, prurigo nodularis, and/or ulcers.

The classification of delusions of parasitosis is complicated. It is considered primarily a monosymptomatic hypochondriacal psychosis and has been associated with schizophrenia, obsessional states, bipolar disorder, depression, and anxiety disorders. Delusions of parasitosis occur primarily in white middle-aged or older women, although the condition has been reported in all age groups and in men.

Savely et al¹ introduced the term Morgellon disease to describe a condition characterized by fibers attached to the skin. The entity appears to be little more than a new designation for delusions of parasitosis. Koblenzer² and Waddell and Burke³ have discussed the utility of the term, with Murase et al⁴ finding the term useful for building a therapeutic alliance with patients with delusions of parasitosis. The Centers for Disease Control and Prevention is currently investigating Morgellon disease.⁵

William Harvey⁶ of the Morgellons Research Foundation Medical Advisory Board states the following:

All patients with Morgellons carry elevated laboratory proinflammatory markers, elevated insulin levels, and verifiable serologic evidence of 3 bacterial pathogens. They also show easily found physical markers such as peripheral neuropathy, delayed capillary refill, abnormal Romberg’s sign, decreased body temperature, and tachycardia. Most importantly they will improve, and most recover on antibiotics directed at the above pathogens.

The author of this article has not found reliable data to back up William Harvey's claims, but they are included here to comprehensively address this issue.

Walling and Swick⁷ suggest abandoning 3 the diagnostic terms trichotillomania, delusions of parasitosis, and neurotic excoriation, which they believe have become barriers to treatment. Instead, they suggest using the alternative patient-centered nomenclature of neuromechanical alopecia, pseudoparasitic dysesthesia, and (simply) excoriation.

Pathophysiology

The cause of delusions of parasitosis is unknown. It appears related to neurochemical pathology. This concept is underlined by its induction by psychoactive agents (eg, amphetamines, cocaine, and methylphenidate) and its coincidence with depression, schizophrenia, social isolation, and sensory impairment.

Frequency

United States

The exact prevalence of delusions of parasitosis is unknown.

International

The exact prevalence of delusions of parasitosis is unknown.

Mortality/Morbidity

The literature includes one report of suicide in a 40-year-old man with delusions of parasitosis.⁸

Race

Delusions of parasitosis appear to be more common in whites than in people of other races.

Sex

Delusions of parasitosis occur primarily in white middle-aged or older women, although the condition has been reported in all age groups and in men. The female-to-male ratio is approximately 2:1. More specifically, this ratio is 1:1 in people younger than 50 years and 3:1 in those older than 50 years.

Age

Delusions of parasitosis are more common in middle-aged and elderly persons than in others. The female-to-male ratio is 1:1 in people younger than 50 years and 3:1 in those older than 50 years.^9,10

Clinical

History

Patients must be queried about their symptoms, the duration of symptoms, and their belief about the etiology. Notably, Goddard¹¹ has described a seasonality to delusions of parasitosis, and Vila-Rodriguez et al discuss the facilitation of delusions of parasitosis resulting from Internet-based dissemination of the condition.¹²
 
The diagnosis and treatment of delusions of parasitosis can be an involved clinical activity. Patients with delusions of parasitosis can resist suggestions that their condition is psychiatric rather than physical and refuse referrals for psychiatric care. In fact, in 35% of patients, the belief of infestation is unshakable.¹³ In approximately 12% of patients, the delusion of infestation is shared by a significant other. This phenomenon is known as folie à deux (eg, craziness for 2) or folie partagé (ie, shared delusions). Variations in this are the conviction that a child, a spouse, or a pet is infested.

The condition of delusions of parasitosis is a monosymptomatic psychosis, a type of psychopathology relatively distinct from the remainder of the personality. If the condition has a defined pathologic or external cause (eg, scabies), it is not truly delusions of parasitosis. In investigating the history of a patient with such suspected delusions, other causes of itch must be investigated. To diagnose this condition, true infestations (eg, scabies), pediculosis, and primary systemic causes of pruritus must be excluded.¹⁴ Examples include hepatitis, HIV infection, dermatitis herpetiformis, thyroid disease, anemia, renal dysfunction, neurologic dysfunction, and lymphoma.

Delusions of parasitosis are distinct from formication. Formication involves the cutaneous sensation of crawling, biting, and stinging. Formication does not involve the fixed conception that skin sensations are induced by parasites. Patients with this condition can accept proof that they do not have an infestation. Many cases of formication remain idiopathic.

Mimics of delusions of parasitosis

Other forms of psychiatric illness can mimic delusions of parasitosis. Such psychiatric illnesses are accompanied by signs of mental illness.

For example, patients with schizophrenia may think they are being attacked by insects as a manifestation of their paranoia.

A type of severe depression termed psychotic depression may cause the patient to believe he or she is contaminated or "dirty" because of insect infestation. Such a patient may have a depressed mood and a sense of helplessness, hopelessness, worthlessness, or excessive guilt. Often, these feelings are obvious at clinical presentation.¹⁵

Drug-induced delusions of parasitosis have been reported during treatment for Parkinson disease.¹⁶

Steinert and Studemund¹⁷ reported a 45-year-old man who did not have a history of psychological pathology, who, after ingesting ciprofloxacin to treat an infection, was overcome with acute delusional parasitosis. He stopped taking the ciprofloxacin, and the delusions of parasitosis resolved altogether without utilization of an antipsychotic agent. Tran et al reported a patient who had delusions of parasitosis after receiving a therapeutic dose of mefloquine,¹⁸ and Krauseneck and Soyka reported an association of delusions of parasitosis with pemoline drug therapy.¹⁹

Cases in which an etiology is defined are best classified as secondary delusions of parasitosis.
Guarneri et al²⁰ noted a patient who was thought to have delusions of parasitosis but who, in fact, had infestation with Limothrips cerealium; they termed the condition pseudo-delusory syndrome (ie, infestation with an uncommon insect).

Ghaffari-Nejad and Toofani²¹ noted a case of secondary delusions of parasitosis in a patient with major depressive disorder who had delusions of oral parasitosis; the patient sensed lizards and small organisms in her mouth.

Physical

Patients with delusions of parasitosis create their rash. They can present with no findings, erosions or ulcers with or without crusts or prurigo nodularis. They may evidence a dermatitis related to attempted treatments, which may include irritating or corrosive cleansers or harsh abrasive devices. Delusions of parasitosis involving the eyelids has been reported.²²

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