Delusional parasitosis also known as delusory parasitosis and delusory cleptoparasitosis, is a form of psychosis or false belief, a "loss of contact with reality". In delusional parasitosis, sufferers have a strong delusional belief that they are infested with parasites, whereas in reality no such parasites are present. Very often the imaginary parasites are reported as being "bugs" crawling on or under the skin; in these cases the experience of the sensation known as formication may be the basis for this belief.
Delusional parasitosis is also referred to as Ekbom's syndrome, named after a Swedish neurologist, Karl Axel Ekbom, who published seminal accounts of the disease in 1937 and 1938. Ekbom's syndrome should not be confused with Wittmaack-Ekbom syndrome, which is another name for restless legs syndrome.
The false belief of delusional parasitosis stands in contrast to actual cases of parasitosis, such as for example, scabies.
People with delusional parasitosis are likely to ask for help not from psychiatrists but from dermatologists, pest control specialists, or entomologists. Because delusional parasitosis is not at all well known to non-specialists, under those circumstances the condition often goes undiagnosed, or may be incorrectly diagnosed.
Delusional parasitosis is divided into primary, secondary functional and secondary organic groups.
In primary delusional parasitosis, the delusions comprise the entire disease entity, there is no additional deterioration of basic mental functioning or idiosyncratic thought processes. The parasitic delusions consist of a single delusional belief regarding some aspect of health. This is also referred to as monosymptomatic hypochondriacal psychosis, and sometimes as "true" delusional parasitosis. In DSM-IV, this corresponds with "delusional disorder, somatic type".
Secondary organic delusional parasitosis occurs when the state of the patient is caused by a medical illness, medication or substance abuse. In the DSM-IV this corresponds with "psychotic disorder due to general medical condition." Physical illnesses that can underly secondary organic delusional parasitosis include: hypothyroidism, cancer, cerebrovascular disease, tuberculosis, neurological disorders, vitamin B12 deficiency, and diabetes mellitus. Any illness or medication of which formication is a symptom or side effect can become a trigger or underlying cause of delusional parasitosis.
Other physiological factors which can contribute to the condition include: menopause (i.e. hormone withdrawal); allergies; drug abuse, including but not limited to cocaine and methamphetamine (as in amphetamine psychosis); certain medical conditions; and poor nutrition. It appears that many of these physiological factors, as well as environmental factors such as airborne irritants, are capable of inducing a "crawling" sensation in otherwise healthy individuals, however some people become fixated on the sensation and its possible meaning, and this fixation may then develop into delusional parasitosis.
Details of delusional parasitosis vary among sufferers, but is most commonly described as involving perceived parasites crawling upon or burrowing into the skin, sometimes accompanied by an actual physical sensation (known as formication). Individuals suffering from this condition may injure themselves in attempts to be rid of the "parasites", and sometimes are able to induce the condition in others through suggestion (a phenomenon dubbed folie à deux).
Nearly any marking upon the skin, or small object or particle found on the person or their clothing, can be interpreted as evidence for the parasitic infestation, and sufferers commonly compulsively gather such "evidence" and then present it to medical professionals when seeking help. This presenting of "evidence" is known as "the matchbox sign".
Delusional parasitosis is seen more commonly in women, and the frequency is much higher past the age of 40.
However, it is also characteristic that sufferers will reject the diagnosis of delusional parasitosis by medical professionals, and very few are willing to be treated, despite demonstrable efficacy of treatment.
The term "Morgellons" was introduced in 2004 to describe a skin condition characterized by lesions and fibers on and under the skin and certain systemic symptoms. A majority of health professionals, including most dermatologists, regard Morgellons as a manifestation of other known medical conditions, including delusional parasitosis and believe any fibers found are from textiles such as clothing. The Morgellons Research Foundation, a non-profit advocacy organization, believes that it is a new infectious disease that will be confirmed by future research. "Other health professionals don't acknowledge Morgellons disease or are reserving judgment until more is known about the condition." Research into the proposed condition is ongoing.