Cases That Test Your Skills

A creepy-crawly disorder

Current Psychiatry. 2005 January;4(1):88-92

References

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Box

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’

Rule out infestation with skin scrapings/biopsy Get a thorough alcohol and drug use history to rule out substance abuse/dependence (particularly stimulant use) Perform a complete physical examination 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 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.

Rule out infestation with skin scrapings/biopsy
Get a thorough alcohol and drug use history to rule out substance abuse/dependence (particularly stimulant use)
Perform a complete physical examination
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
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.