Delusional Parasitosis

Delusional parasitosis (DP) is a fixed and false belief characterized by a person’s preoccupation of being infested by insects, worms, or other living organisms.
It is a specific form of somatic (health-related) delusion and is considered a somatic disorder once the belief endures 1 mo or greater. ¹

Synonyms

Delusional infestation
Delusory parasitosis
Morgellons disease
Ekbom syndrome

ICD-10CM CODE
F22	Delusional disorders
DSM-5 CODE
297.1 (F22)	Delusional disorder

Epidemiology & Demographics

Incidence

Rare; affects 0.8 to 1.9 per 100,000 person years ²

Prevalence

Rare; cases secondary to substance use or other psychiatric disorders may be more common

Predominant Sex & Age

Average age of onset >55; incidence higher in females ³

Peak Incidence

Sixth decade of life; there is a small peak in the third decade associated with substance use. Studies report that the duration of illness can range from days up to 35 yr, with an average duration of 3 yr. ²

Risk Factors

Social isolation, vision impairment, preexisting skin disease or neuropathy, and history of psychiatric illness are risk factors.
Substance use, particularly the use of cocaine or methamphetamine, is also a risk factor.
Numerous case reports describe the development of shared delusions (folie à deux) in individuals close to patients with delusional parasitosis.

Genetics

Unknown

PHYSICAL FINDINGS & CLINICAL PRESENTATION

•Patients complain of being infested by living organisms. The patients’ distress is out of proportion to physical exam or laboratory test findings. Due to their hallmark lack of insight, patients are not relieved when workup exonerates infection.
•Patients may experience itching (pruritus) or tactile hallucinations of crawling or biting sensations (formication). Skin may show evidence of excoriations. ⁴
•Many patients describe a specific exposure event, such as a bug bite, recent travel, or exposure to a contaminated environment.
•Patients have often been to multiple specialists, including dermatologists, allergists, and infectious disease specialists.
•Patients commonly bring in samples of skin or fibers (“specimen sign”), or photos (“digital specimen sign”), with no observable evidence of infestation. This behavior was previously referred to as the “matchbox sign,” as patients would collect debris in matchboxes and present it as evidence during visits.

What causes Delusional Parasitosis?

•Pathophysiology is poorly understood. Excess dopaminergic transmission through decreased dopamine transporter function may be involved, similar to other psychotic disorders. ³ This is supported by findings that medications that inhibit dopamine reuptake (such as amphetamines) can induce similar symptoms.

Differential Diagnosis

•Primary delusional parasitosis refers to the delusion of being infested by living organisms in the absence of other disorders and is considered a variant of delusional disorder, somatic type. Secondary delusional parasitosis refers to delusions occurring secondarily to other medical or psychiatric disorders. Delusional infestation can occur secondary to schizophrenia and psychotic mood disorders. Intrusive, ego-dystonic thoughts about infestation can occur in obsessive-compulsive disorder.
•Substance and medication effects are associated with delusional parasitosis. These substances include amphetamines, cocaine, alcohol, and cannabis. Medications include corticosteroids, topiramate, and dopamine agonists (pramipexole and ropinirole). ⁵
•Delusions of infestation can occur in delirium, as well as a variety of neurologic and medical conditions such as dementia, stroke, multiple sclerosis, nutritional deficiencies, uremia, hyperthyroidism, malignancy, and infection (HIV, syphilis). ⁶
•Dermatologic conditions associated with pruritus can be confused with delusional parasitosis in the absence of correct diagnosis. Examples include actual mite infestations (i.e., scabies), irritant contact dermatitis (i.e., fiberglass), and herpes zoster.

Workup

•A thorough history is likely to yield the highly fixed nature of the belief and an unwillingness on the patient’s part to accept the lack of findings on physical exam.
•First, a true parasitosis should be ruled out. A skin biopsy may exclude dermatitis herpetiformis or certain forms of irritant contact dermatitis. ⁷
•Review the patient’s medication list and inquire about substance use.
•A safety assessment should be performed to assess whether a patient can safely care for self. Some patients may dangerously resort to applying insecticides to their skin in an effort to “treat” their infestation.

Laboratory Tests

•Every patient should undergo basic screening labs including a CBC, Chem 7, erythrocyte sedimentation rate, C-reactive protein, thyroid-stimulating hormone, and urine toxicology. ⁶
•Expanded workup may include other infectious (HIV, syphilis, viral hepatitis) and nutritional (B ₁₂, folate) studies. ⁶
•Obtain baseline lipid panel and hemoglobin A1C if initiating antipsychotic medications.
•If the patient has already visited multiple healthcare providers and received a comprehensive workup, a repeat workup is not indicated.

Imaging Studies

•There are no radiographic tests involved in the diagnosis of delusional parasitosis.

Treatment

•For treatment of delusional parasitosis, antipsychotics have been shown to be effective in 60% to 100% of cases, with median onset of clinical response of 1.5 wk. ⁷ Compliance is a challenge.
•The atypical antipsychotic, risperidone, is considered first line in the treatment of delusional parasitosis. Low-dose olanzapine has also been shown to be effective. Aripiprazole and ziprasidone have shown promise but require further study. Classically, pimozide was the treatment of choice, although it has been associated with QTc prolongation and is now less-favored than atypical antipsychotics. ³
•Antipsychotics have been associated with weight gain, metabolic syndrome, QTc prolongation, movement disorders, and increased risk of death in the elderly.
•Given all of these issues, a careful risk-benefit analysis is needed, including the assistance of family members of elderly patients.
•Symptomatic management of pruritus includes antihistamines and topical steroids.
•Treatment of secondary delusional parasitosis should focus on treating the underlying or psychiatric disorder.

Non Pharmacologic Therapy

•A nonjudgmental approach and the establishment of a therapeutic relationship are critical to successful management.
•Cognitive behavioral therapy can be helpful in augmenting patient acceptance and efficacy of pharmacologic treatment. ³
•Given the fixed nature of the belief, patients often refuse referral to a mental health specialist.
•Some cases of delusional parasitosis spontaneously resolve.

Acute General Treatment

Antipsychotics ( Table E1 )

TABLE E1 Antipsychotics

Antipsychotic Drug	Dosage
Risperidone	0.5-4 mg PO daily
Olanzapine	2.5-12.5 mg PO nightly
Aripiprazole	2-30 mg PO daily
Ziprasidone	20-80 mg PO BID
Quetiapine	12.5-80 mg PO nightly
Haloperidol	0.5-10 mg PO nightly
Pimozide	0.5-10 mg PO daily

BID, Twice per day; PO, by mouth.

Complementary & Alternative Medicine

There is no evidence on the use of complementary or alternative medicine for this disorder.

Referral

Referral to an outpatient psychiatrist may be helpful, but patients are often resistant. Patients are typically more accepting of treatment from a dermatologist.

Prevention

No preventive measures have been identified.

Patient & Family Education

Psychoeducation may be helpful for the patient and family, although resistance from the patient can be expected.

References

1.American Psychiatric Association: Schizophrenia spectrum and other psychotic disorders : In American Psychiatric Association, ed. Diagnostic and statistical manual of mental disorders . 2013 . American Psychiatric Association , Washington, DC

2.Assalman I., et al.: Treatments for primary delusional infestation . Cochrane Database Syst Rev 2019; 12: pp. CD011326.

3.Reich A., et al.: Delusions of parasitosis: an update . Dermatol Ther 2019; 9 (4): pp. 631-638.

4.Boggild A.K., et al.: Delusional parasitosis: six-year experience with 23 consecutive cases at an academic medical center . Int J Infect Dis 2010; 14 (4): pp. e317-e321.

5.Kemperman P.M.J.H., et al.: Drug-induced delusional infestation . Acta Derm Venereol 2022; 102: adv00663 .

6.Ansari M.N., Bragg B.N.: Delusions of parasitosis . StatPearls, Treasure Island . 2022. StatPearls Publishing , FL

7.Campbell E.H., et al.: Diagnosis and management of delusional parasitosis . J Am Acad Dermatol 2019; 80 (5): pp. 1428-1434.

Delusional Parasitosis