eMedicine Specialties > Dermatology > Psychocutaneous Diseases
Delusions of Parasitosis
Updated: Feb 12, 2008
Introduction
Background
Delusions of parasitosis (DP) 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 DP is complicated. It is considered primarily a monosymptomatic hypochondriacal psychosis and has been associated with schizophrenia, obsessional states, bipolar disorder, depression, and anxiety disorders. DP occurs primarily in white middle-aged or older women, although it has been reported in all age groups and in men.
Medscape Resource Centers for Schizophrenia, Bipolar Disorder, Depression, and Anxiety Disorders may provide helpful additional information.
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 DP. 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 DP. 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:
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.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.
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. For additional information on the other topics mentioned, see Trichotillomania and Neurotic Excoriations.
Pathophysiology
The cause of DP 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 DP is unknown.
International
The exact prevalence of DP is unknown.
Mortality/Morbidity
The literature includes one report of suicide in a 40-year-old man with DP.8
Race
DP appears to be more common in whites than in people of other races.
Sex
DP occurs primarily in white middle-aged or older women, although it 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
This disease is more common in middle-aged and elderly persons than in others. The male-to-female ratio is 1:1 in people younger than 50 years and 3:1 in those older than 50 years.
Clinical
History
Patients must be queried about their symptoms, the duration of symptoms, and their belief about the etiology. Notably, Goddard9 has described a seasonality to DP.
The diagnosis and treatment of DP can be an involved clinical activity. Patients with DP 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. 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.
DP 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 DP. 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. Examples include hepatitis, HIV infection, dermatitis herpetiformis, thyroid disease, anemia, renal dysfunction, neurologic dysfunction, and lymphoma.
DP is 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 DP
Other forms of psychiatric illness can mimic DP. 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.10
Drug-induced delusions of parasitosis have been reported during treatment for Parkinson disease.11
Steinert and Studemund12 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 DP resolved altogether without utilization of an antipsychotic agent. Cases in which an etiology is defined are best classified as secondary DP.
Guarneri et al13 noted a patient who was thought to have DP 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 Toofani14 noted a case of secondary DP 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 DP create their skin 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.
More on Delusions of Parasitosis |
 Overview: Delusions of Parasitosis |
| Differential Diagnoses & Workup: Delusions of Parasitosis |
| Treatment & Medication: Delusions of Parasitosis |
| Follow-up: Delusions of Parasitosis |
| References |
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References
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Further Reading
Keywords
DP, DOP, insect infestation, matchbox sign, monosymptomatic hypochondriacal psychosis, delusion of infestation, delusional parasitosis, delusional infestation, folie à deux, folie partagé, morgellons disease.
