Delusional parasitosis (DP), also called delusional infestation,^[2] is a mental health condition where a person falsely believes that that their body is infested with living or nonliving agents. Common examples of such agents include parasites, insects, or bacteria. This is a delusion due to the belief persisting despite evidence that no infestation is present.^[3][1] People with this condition may have skin symptoms such as the urge to pick at one's skin (excoriation) or a sensation resembling insects crawling on or under the skin (formication). Morgellons disease is a related constellation of symptoms. This self-diagnosed condition is considered a form of a type of delusional parasitosis. People with Morgellons falsely believe harmful fibers are coming out of their skin and causing wounds.^[1][4]

Delusional parasitosis is classified as a delusional disorder in the fifth revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). The precise cause is unknown. It may be linked to problems with dopamine in the brain, similar to psychotic disorders.^[2] Diagnosis requires the delusion to be the only sign of psychosis, not caused by another medical condition, and present for at least a month. A defining characteristic of delusions is that the false belief cannot be corrected.^[5] As a result, most affected individuals believe their delusion is true and do not accept treatment.^[2] Antipsychotic medications can help with symptom remission.^[6] Cognitive behavioral therapy and antidepressants can also decrease symptoms.^[1][7]

The condition is rare and affects women twice as much as men.^[1] The average age of individuals affected by the disorder is 57.^[8] Ekbom's syndrome is another name for the condition. This name honors the neurologist Karl-Axel Ekbom, who published accounts of the disease in 1937 and 1938.^[1]

Delusional parasitosis is classified as a delusional disorder of the somatic subtype in the Diagnostic and Statistical Manual of Mental Disorders (DSM5).^[1][5] Since 2015, the most common name for the disorder is delusional parasitosis. The condition has also been called delusional infestation, delusory parasitosis, delusional ectoparasitosis, psychogenic parasitosis, Ekbom syndrome, dermatophobia,parasitophobia, formication and "cocaine bugs".^[5]

Delusional parasitosis can occur in two different forms.^[5] The first, primary delusional infestation, is a psychiatric disorder.^[2] The second, secondary delusional infestation, is linked to other medical or psychiatric conditions.^[2] In contrast, delusory cleptoparasitosis is a delusion where the person believes the infestation is in their home.^[9]

Morgellons is a constellation of symptoms considered a form of delusional parasitosis. This self-diagnosed condition is similar to other delusional infestations. People with this condition have painful skin sensations. They believe this is caused by fibers that are present in their lesions.^[1][5] Morgellons disease is not listed in the International Classification of Diseases (ICD-11).^[4]

People with delusional parasitosis believe that "parasites, worms, mites, bacteria, fungus" or similar organisms have infected them. Reasoning or logic cannot change this fixed, false belief.^[5] Symptoms can differ among those with the condition. It often involves a crawling or pin-pricking sensation. Many describe it as a sensation of parasites crawling upon or burrowing into the skin. Sometimes, this includes a physical sensation (known as formication).^[1][5][8] People with this condition may injure themselves trying to remove the "parasites". This can lead to skin damage such as excoriation, bruises, and cuts. Moreover, using harsh chemicals or cleaning obsessive can cause further harm.^[8]

People with this condition recall events like a bug bite, travel, sharing clothes, or contact with someone they think was infected.^[1] These exposures may cause the individual to pay attention to bodily sensations they usually ignore. The individual may then believe these symptoms are due to an infestation.^[1] Those affected may see any skin mark or small object on them or their clothing as proof of a parasitic infestation. Those with the condition often collect such "evidence" to present to medical professionals. Medical professionals call this the "matchbox sign", "Ziploc bag sign" or "specimen sign." The name stems from the fact that the evidence is typically stored in a small container, like a matchbox.^[1][8] The matchbox sign is present in five to eight out of every ten people with DP.^[1] Related is a "digital specimen sign", in which individuals bring collections of photographs to document their condition.^[1]

Similar delusions may be present in close relatives. This is known as a folie à deux and it occurs in 5–15% of cases.^[8] It is considered a shared psychotic disorder.^[8] The internet has created a unique situation where many people can reinforce shared delusions. This has led to the term "folie à Internet" for delusional parasitosis. When those affected are isolated from each other, their symptoms usually improve, but most still need treatment.^[8]

Approximately eight out of ten individuals with DP have co-occurring conditions, such as depression, substance use disorders, and anxiety. Their personal and professional lives are frequently disrupted due to extreme distress regarding their symptoms.^[10]

The cause of delusional parasitosis is unknown. Primary delusional parasitosis may result from high dopamine in the brain's striatum. This happens from diminished dopamine transporter (DAT) function.^[1][8] The dopamine transporter regulates dopamine reabsorption in the brain.^[1][8] For example, substances that block dopamine reuptake, like cocaine and methylphenidate, can cause symptoms like formication. Additionally, several conditions linked to faulty dopamine transporters can also lead to secondary delusional parasitosis. Examples of such conditions include: "schizophrenia, depression, traumatic brain injury, alcoholism, Parkinson's and Huntington's diseases, human immunodeficiency virus infection, and iron deficiency".^[8] Providing further support for the dopamine theory, antipsychotics improve DP symptoms. This may be because they affect dopamine transmission.^[8][5]

Secondary delusional parasitosis is caused by another medical or psychiatric disorder. Medical conditions associated with secondary delusional parasitosis include: deficiencies in vitamins such as B12 or folate, thyroid dysfunction, diabetes, Parkinson's disease, dementia, encephalitis, meningitis, and multiple sclerosis.^[8][5] Additionally, some infectious diseases such as HIV and syphilis have also been associated with delusional infestation.^[5] Secondary delusional parasitosis is also associated with substance use disorders. The most commonly associated substances include chronic alcohol use, alcohol withdrawal, long-term cocaine use, long-term amphetamine use.^[5] Finally, there also a number of prescription drugs that may cause DP as a side effect. These include "phenelzine, pargyline, ketoconazole, corticosteroids, amantadine, ciprofloxacin, pegylated interferon alpha, and topiramate."^[5]

Delusional parasitosis is diagnosed when: 1) the delusion is the only symptom of psychosis, 2) the delusion has lasted a month or longer, 3) the person's behavior is otherwise not markedly odd or impaired, 4) mood disorders (if present at any time) have been comparatively brief, and 5) the delusion cannot be better explained by another medical condition, mental disorder, or the effects of a substance. For diagnosis, the individual must attribute abnormal skin sensations to the belief that they have an infestation, and be convinced that they have an infestation even when evidence shows they do not.^[1]

The condition is recognized in two forms: primary and secondary. In primary delusional parasitosis, the delusions are the only manifestation of a psychiatric disorder. Secondary delusional parasitosis occurs when another psychiatric condition, medical illness or substance (prescription or recreational) use causes the symptoms. In secondary delusional infestation, the delusion is a symptom of another condition rather than the disorder itself.^[5] Secondary forms of DP can be functional (due to psychiatric disorders) or organic (due to other medical illness or organic disease).^[8] The secondary organic form may be related to vitamin B₁₂ deficiency, hypothyroidism, anemia, hepatitis, diabetes, HIV/AIDS, syphilis, or use of stimulants like methamphetamine and cocaine.^[8][11]

The first step in diagnosis is to conduct a comprehensive examination to rule out other causes of the person's symptoms.^[8] Testing to rule out other conditions fosters trust between the provider and the person affected.^[10] To check for parasitic infestations, providers use skin examinations, skin biopsies, dermatologic tests and laboratory analyses. ^[1][10] A detailed lab analysis can rule out other causes. Examples of such analyses include complete blood count, comprehensive metabolic panel, erythrocyte sedimentation rate, C-reactive protein, urinalysis for toxicology and thyroid-stimulating hormone.^[1][10] Tests may also be done for "human immunodeficiency virus, syphilis, viral hepatitis, B₁₂ or folate deficiency", and allergies.^[1] Additionally, the provider might review medications that may cause similar symptoms.^[8]

Healthcare professionals first distinguish delusional parasitosis from actual infections like scabies or mites.^[12] Other possible causes of these symptoms include exposure to agricultural products or fiberglass, pet-induced dermatitis, and moth/caterpillar dermatitis.^[10]

Providers may also check for other related psychiatric conditions. Examples include schizophrenia, anxiety disorders, obsessive–compulsive disorder, dementia, delirium, affective or substance-induced psychoses, and medical conditions that cause psychosis.^[10] Several drugs may also cause such symptoms, such as amphetamines, dopamine agonists, opioids, and cocaine.^[10] Providers may also check for medical conditions that may cause such symptoms. Examples include hypothyroidism, and kidney or liver disease.^[10]

Many of these physiological and environmental factors are capable of inducing a "crawling" sensation. It is considered a delusion when one becomes fixated on the sensation and its possible meaning. This fixation may develop into DP.^[13]

People with delusional parasitosis are not comforted by the lack of evidence for infestation.^[10] Additionally, many people will reject the diagnosis of delusional parasitosis. As a result, these people may also reject treatment for the condition.^[1][5][14] Confronting individuals about delusions is unhelpful because the delusions are not likely to change.^[8]

Individuals with delusional infestation often see many providers in different specialties. Treatment guidelines emphasize the importance of gaining the person's trust and collaborating with other providers.^[8] Dermatologists may have more success introducing the use of a medication as a way to alleviate the distress of itching.^[8]

As of 2019, there have not been any studies that compare available treatments to placebo.^[15] The only treatment that provides a cure is low doses of antipsychotic medication. Risperidone is the treatment of choice.^[1] In the past, the treatment of choice was pimozide. This treatment has grown out of favor due to a higher side effect profile.^[10] Aripiprazole and ziprasidone are effective but have not been well studied for delusional parasitosis. Olanzapine is also effective. Antipsychotics are used at the lowest possible dosage. They are increased gradually until symptoms remit.^[1] Cognitive behavioral therapy (CBT) has also been effective.^[10][8]

People will often have symptoms for months before being diagnosed.^[1] The average duration of the condition is about three years.^[1] If not treated, symptoms will typically worsen. People may develop chronic scarring as a result. ^[9] Antipsychotics or treating the underlying condition may cure delusional parasitosis.^[1]

Delusional parasitosis drastically impacts the lives of those affected. The condition leads to social isolation which can worsen depressive symptoms. ^[1] Additionally, the condition often affects people's self esteem. ^[9] Depression and suicide risk is elevated in people affected by delusional parasitosis. The condition can also impact the individuals ability to function in their daily life. This can negatively impact employment.^[1]

Delusional parasitosis is a rare disorder. It is the most common of the hypochondriacal psychoses.^[5] It is more common than other types of delusions, like those associated with body odor or halitosis.^[5] DP is often undetected because those who have the condition may not consult a psychiatrist.^[5] This makes it difficult to estimate the number of people with delusional parasitosis. A population-based study in Olmsted County, Minnesota, found a prevalence of 27 per 100,000 person-years and an incidence of almost 2 cases per 100,000 person-years.^[5] Other studies have found annual incidence rates to be anywhere from 2-17 cases per 1 million people per year.^[9] Of note, the majority of dermatologists will see at least one person with DP during their career.^[8]

The condition is observed twice as often in women than men. The highest incidence occurs in people in their 60s. There is also a higher occurrence in people in their 30s, associated with substance use.^[1] It occurs most often in "socially isolated" women with an average age of 57.^[8] Individuals with DP may be high functioning.^[9]

Karl-Axel Ekbom, a Swedish neurologist, first described delusional parasitosis as "pre-senile delusion of infestation" in 1937.^[1] The common name has changed many times since then. Ekbom originally used the German word dermatozoenwahn, but other countries used the term Ekbom's syndrome. That term fell out of favor because it also referred to restless legs syndrome (more specifically termed Willis–Ekbom disease (WED) or Wittmaack-Ekbom syndrome).^[16][17] Other names that referenced "phobia" were rejected because anxiety disorder was not typical of the symptoms.^[17] The eponymous Ekbom's disease was changed to "delusions of parasitosis" in 1946 in the English literature, when researchers J Wilson and H Miller described a series of cases, and to "delusional infestation" in 2009.^[1][18] The most common name since 2015 has been "delusional parasitosis".^[5]

Ekbom's original was translated to English in 2003; the authors hypothesized that James Harrington (1611–1677) may have been the "first recorded person to suffer from such delusions when he 'began to imagine that his sweat turned to flies, and sometimes to bees and other insects'."^[19]

Mary Leitao, the founder of the Morgellons Research Foundation,^[20] coined the name Morgellons in 2002, reviving it from a letter written by a physician in the mid-1600s.^[21][22] Leitao and others involved in her foundation (who self-identified as having Morgellons) successfully lobbied members of the U.S. Congress and the U.S. Centers for Disease Control and Prevention (CDC) to investigate the condition in 2006.^[23][24] The CDC published the results of its multi-year study in January 2012. The study found no underlying infectious condition and few disease organisms were present in people with Morgellons; the fibers found were likely cotton, and the condition was "similar to more commonly recognized conditions such as delusional infestation".^[25]

Since the early 2000s, a strong internet presence has led to increasing self-diagnosis of Morgellons.^[1] An active online community has supported the notion that Morgellons is an infectious disease, and propose an association with Lyme disease. Publications "largely from a single group of investigators" describe findings of spirochetes, keratin and collagen in skin samples of a small number of individuals; these findings are contradicted by the much larger studies conducted by the CDC.^[5]

Jay Traver (1894–1974), a University of Massachusetts entomologist, has been characterized after her death as having made "one of the most remarkable mistakes ever published in a scientific entomological journal",^[26] after publishing a 1951 account of what she called a mite infestation.^[27] Her detailed description of her own experience with mites was later shown to be incorrect,^[26] and has been described by others as a classic case of delusional parasitosis.^{[28][16][29][30]} Matan Shelomi says the paper has done "permanent and lasting damage" to people with delusional parasitosis, "who widely circulate and cite articles such as Traver's and other pseudoscientific or false reports" via the internet, making treatment and cure more difficult.^[29] He argues that the historical paper should be retracted because it has misled people about their delusion and that papers "written by or enabling deluded patients", along with internet-fed conspiracies and the related delusion of Morgellons, may increase.^[29]

Shelomi published another study in 2013 of what he called scientific misconduct when a 2004 article in the Journal of the New York Entomological Society included what he says is photo manipulation of a matchbox specimen to support the claim that individuals with DP are infested with collembola.^[31]

• Stimulant psychosis
• Formication