Delusional parasitosis

# Overview
Delusional parasitosis is a form of psychosis in which sufferers hold a delusional belief they are infested with parasites.
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. It is not to be confused with Wittmaack-Ekbom syndrome (restless legs syndrome).

# Classification
Delusional parasitosis is divided into primary, secondary functional and secondary organic groups.

## Primary
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 functional
Secondary functional delusional parasitosis occurs when the delusions is associated with a psychiatric condition such as schizophrenia or clinical depression.

## Secondary organic
Secondary organic delusional parasitosis occurs when the state of the patient is caused by a medical illness, medication or substance abuse. In 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 of 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; 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 the "crawling" sensation in otherwise healthy individuals, but that some people become fixated on the sensation, and this fixation may then develop into delusional parasitosis.

# Presentation
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 a 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. The condition is seen most commonly in women, and the frequency is much higher past the age of 40.

# Differential Diagnosis of Delusional parasitosis

# Diagnosis

## Physical Examination

### Skin
- Delusional parasitosis. Adapted from Dermatology Atlas.
- Delusional parasitosis. Adapted from Dermatology Atlas.

# Treatment
Treatment of secondary forms of delusional parasitosis are addressed by treating the primary associated psychological or physical condition. The primary form is treated much as other delusional disorders and schizophrenia. In the past, pimozide was the drug of choice when selecting from the typical antipsychotics.  Currently, atypical antipsychotics such as olanzapine or risperidone are used as first line treatment.  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.

# Morgellons
The term "Morgellons" was introduced in 2002 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 condition is ongoing.