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Cases that Test Your Skills

A creepy-crawly disorder

Three months after spotting mites on her arm, Mrs. K believes she and her house are infested. No medical evidence is found, but she’s convinced the problem is not ‘in her head.’

Vol. 4, No. 1 / January 2005

History: A mite disturbing

Mrs. K, age 60, a social worker, saw mites on her arm 3 months ago while going through a client’s old belongings. Since then, she reports, she and her house have become infested with mites.

Despite using copious amounts of lotions, baths, sprays, and prescription creams, she sees increasingly visible “creatures” all over her body and in her stool. Three doctors found no physical evidence of infestation, however, and she became indignant after one told her the problem is “in her head.”

A veterinarian treated Mrs. K’s cat for mites. Days later, Mrs. K suspected that the cat had become reinfested at home and returned it to the veterinarian. He assured her the cat was fine, but she was afraid to bring it home. The cat has remained at the veterinarian’s office—to the doctor’s displeasure—for weeks.

Two weeks after Mrs. K first spotted the mites, her husband, age 82, started believing he is infested. Mr. K, who is retired, has battled depression and drinks about a half-gallon of liquor daily.

After 2 months, Mrs. K quit her job for fear she would infest her co-workers, then locked herself and her husband in their house and allowed no visitors. Day and night for nearly 3 weeks, Mrs. K repeatedly vacuumed the house, shampooed the carpets, and sprayed the walls and furniture with a homemade insecticide. She taped the windows closed to keep bugs out and covered all furniture and surface areas with plastic. A toxic stench of insecticide and shampoo permeated every room.

A neighbor told Mrs. K’s son that his parents were locked inside their house. He came over and knocked on their door, but was refused entry. He eventually got Mrs. K out by threatening to call the police, then brought her to the emergency room.

At presentation, Mrs. K’s right leg has scratches and scabs caused by frequent scratching at mites she saw there. Her hands are reddened and dry, suggesting chemical dermatitis caused by cleaning and repeated insecticide use. Ritual cleaning and spraying has kept her from eating or sleeping; she has lost 12 lbs over 3 weeks and looks pale and tired.

A recovered alcoholic, Mrs. K has been sober for 12 years. She has no other psychiatric, medical, or dermatologic history, and has few social contacts beyond her family and workplace acquaintances.

Blood chemistry, CBC, and urine drug test results are normal. Head MRI reveal no neurologic abnormalities. Her Mini-Mental State Examination (MMSE) score (29/30) indicates no cognitive impairment.

Mrs. K is hospitalized to separate her from her allegedly bug-infested household and husband. At intake, she is panicked over leaving her husband alone and distressed that no one except she and her husband can see the bugs infesting their house and covering her skin. She asks doctors to test a small piece of toilet paper, which she says contains a sample of the bugs. She also fears that she infested her son by letting him into her house.

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The authors’ observations

Mrs. K’s presentation and clinical course suggest delusional parasitosis, a fixed false belief of a parasitic infestation that can cause significant social and occupational dysfunction and medical problems. One patient calls this disorder “bugaphobia.”

The disorder may start as a self-perceived invisible infestation and evolve into visual hallucinations of bugs. Patients usually believe their skin is infested; some believe their internal organs, gums, or skin and internal organs are infested.1,2

Table 1

Medical conditions that may precede delusional parasitosis

Anemia (severe)


CNS infections

Head injury



Hypovitaminosis of vitamin B12, folate, or thiamine

Multiple sclerosis

Pulmonary disease

Renal disease

Rheumatologic disease

Sight or hearing loss

Source: Reference 6

Skin lesions can result, including physical trauma from picking at sites the patient believes is infested. Some patients have sustained ocular trauma from picking at their eyes, which they believed contained insects.2 At least one patient, depressed after failing to kill the parasites, killed himself.1 As with Mrs. K, profuse use of insecticides or topical sprays can cause chemical dermatitis. Many patients isolate themselves to avoid infesting others.3

Some patients misinterpret scabs, abrasions, or skin irritation secondary to pesticide use as signs of infestation. Delusional parasitosis can also develop after a real, one-time infestation, as may have happened with Mrs. K.

Convinced they are infested, patients consult multiple providers—including dermatologists, gastroenterologists, and ophthalmologists—in search of the “right” treatment. They undergo numerous tests or procedures and repeatedly apply prescription creams and lotions, leading to chemical dermatitis. Patients often try to prove they are infested by bringing skin, dirt, or toilet tissue samples to doctors—this is called the “matchbox sign” because patients generally bring these samples in small boxes.4 They also may repeatedly ask veterinarians to disinfest their pets.


Neurobiologic theories behind delusional parasitosis

Described as early as 1892, delusional parasitosis has been called acrophobia, dermatophobia, parasitophobic dermatitis, parasitophobia, entomophobia, and other names.12 Researchers disagree on whether it is a primary psychiatric disorder or is secondary to a mental or physical disorder.13

Researchers have debated two neurobiologic explanations behind the disorder:

Primary sensory. Perrin in 1896 suggested that the parasitosis starts as a sensory misinterpretation, is transformed to a tactile hallucination, then becomes delusional.3

Primary delusional. Others believe delusional parasitosis starts as a hallucination, after which somatic delusional properties develop.3 Some theorists suggest that the symptoms are consistent with thalamic and parietal dysfunction or that the disorder may be a type of late-onset schizophrenia.8

Behaviors associated with “bugaphobia” may be “hardwired” into our evolutionary biology. For example, skin picking may be related to primitive grooming behavior. Its contagiousness may have its roots in animalistic pack behaviors, through which creatures adapt by copying behaviors of others in the pack.8

Patients, however, do not believe the disorder is psychiatric5 and resist seeing a psychiatrist. Often a primary care physician or dermatologist calls on a psychiatrist as a consultant,6 as happened here.

Delusional parasitosis is most often found in socially isolated women age >40 of average or higher intelligence. Persons in some cultures may be more susceptible than others to some types of parasitic delusions. For example, several persons in India who considered ear cleanliness crucial to attaining cultural and spiritual purity reported having ear infestation.7

Delusional parasitosis also is associated with:

  • medical conditions (Table 1)6
  • use of cocaine, amphetamines, 8 corticosteroids, 3,9 or phenelzine10
  • occipital-temporal cerebral infarction11
  • cognitive impairment related to dementia, depression, mental retardation, or schizophrenia/schizophreniform disorder.

Cognitive impairment secondary to a medical problem may foster the delusion, or the patient may misinterpret a physical symptom as evidence of internal infestation. For example, a patient with chronic stomach pain may think he has bugs in his gut.5

Mrs. K’s delusional parasitosis may be a primary psychiatric disorder (Box). She is medically healthy and does not use drugs or alcohol. Her MMSE score is essentially normal, and she exhibited no psychotic symptoms or loss of function before her first mite sighting.

Diagnosis. Delusional parasitosis is diagnosed as delusional disorder, somatic type, if symptoms persist >1 month. Thorough laboratory and neurologic evaluation is recommended to rule out medical causes (Table 2). Eliminate schizophrenia and schizophreniform disorder with a detailed patient history and cognitive testing.

Also check for a comorbid psychiatric disorder that may be perpetuating the delusion. Delusional parasitosis often co-occurs with axis I disorders including major depressive disorder, substance abuse, dementia, and mental retardation.

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The authors’ observations

Mr. K’s “bugaphobia” most likely was a form of shared secondary delusion called folie-a-deux. Between 11% and 25% of persons with primary delusional parasitosis induce secondary delusional parasitosis in another person, usually a spouse or longtime friend. 2 About 50% of folie-a-deux disorders involve a married couple. Often both partners are socially isolated.4

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Treatment: Between two worlds

Mrs. K was given risperidone, 2 mg/d, for delusions and anxiety, and escitalopram, 10 mg/d, preventatively for a suspected underlying depression.

As her symptoms began to clear across 2 to 3 days, Mrs. K realized most times that she was not infested, but on occasion still feared that she was. She continued to worry about her husband being alone in a mite-infested house. We reassured her that her husband would be OK and told her to let us know if the mites resurfaced on her skin.

The authors’ observations

Building rapport. When treating delusional parasitosis, be accepting and non-confrontational. These patients tend to switch doctors until they find someone who understands their problem. Developing rapport can promote treatment adherence and prevent or minimize relapse.

Table 2

5 steps to confirm ‘bugaphobia’

  1. Rule out infestation with skin scrapings/biopsy
  2. Get a thorough alcohol and drug use history to rule out substance abuse/dependence (particularly stimulant use)
  3. Perform a complete physical examination
  4. Order a CBC, urinalysis, liver function tests, thyroid function test, vitamin B 12 , folate, iron studies, blood urea nitrogen, serum electrolytes, and glucose to screen for associated medicalconditions
  5. Order head CT or MRI to rule out infarction or mass

Source: Adapted from Driscoll MS, Rothe MJ, Grant-Kels JM, Hale MS. Delusions of parasitosis: a dermatologic, psychiatric, and pharmacologic approach. J Am Acad Dermatol 1993;29:1023-33.

Start by getting the patient to leave the environment that feeds the delusion. Tell the patient, for example, “The hospital may have experts on your disorder who can help you.” Hospitalize the patient if he or she cannot function independently or will not leave the offending environment. Wait 1 to 2 days before starting medication to see if symptoms remit spontaneously, which they frequently do.4

Also communicate with other specialists to gauge medication history, confirm test findings, and rule out medical causes.

Pharmacotherapy. If symptoms do not resolve after 1 or 2 days of observation, look for a comorbid medical or mental disorder. Prescribe an atypical antipsychotic such as risperidone, 2 to 4 mg/d, or olanzapine, 2.5 mg/d, both of which have been effective against delusional parasitosis. 14,16 Keep dosages low to reduce risk of sedation, extrapyramidal symptoms (EPS), and tardive dyskinesia.

Suggesting a psychotropic to patients who are convinced their problem is not psychiatric can be difficult. Try saying:

  • Some people are more sensitive than others to sensations on their skin or in their body. This medication will help you tolerate the sensations.”
  • or, “This drug will help reduce the anxiety your problem is causing.”

If symptoms persist another 3 days, try a different atypical or a conventional neuroleptic. Watch for EPS or other neuroleptic-related side effects in patients age >65.

Pimozide has shown efficacy against delusional parasitosis in placebo-controlled trials, 17,18 but it can alter cardiac conduction, especially at higherthan-recommended dosages. Start pimozide at 1 mg/d and increase by 1 mg/week until clinical response is achieved. Most patients respond to dosages used to treat psychotic disorders (4 to 10 mg/d). 19 Order a baseline and periodic ECG to monitor for QTc prolongation, and do an abnormal involuntary movement scale examination every 3 to 6 months to test for EPS.

Other treatments that have shown benefit in case reports include naloxone, 10 mg/d; 20 haloperidol, 10 mg/d; trifluoperazine, 15 mg/d; chlorpromazine, 150 to 300 mg/d; and electroconvulsive therapy.7

We have found that prognosis usually is poor after first- and second-line treatments have failed. Continue to search for a missed disorder, and add an antidepressant if an underlying depression is found or suspected.

Psychotherapy. Perform supportive and harm reduction psychotherapy immediately after diagnosis. Supportive, rapport-building approaches can get the patient to comfortably discuss the issues that led to the delusion and help him/her confront a relapse. Harm reduction can discourage patients from requesting unnecessary invasive tests, using medications and toxic insecticides, or other potentially harmful behaviors.

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