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Delusional infestation

What nurses should know

Windbiel-Rojas, Karey MS; Matuskey, Rachel BSN, RN; Parilo, Denise Wall PhD, RN

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doi: 10.1097/01.NURSE.0000757152.58008.d1
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DELUSIONAL INFESTATION is a rare psychiatric disorder in which a person has a false and fixed belief of being infested with organisms such as parasites, mites, bacteria, or fungi despite a lack of clinical evidence to support this belief.1,2 A common manifestation of delusional infestation is the feeling of crawling organisms in or on the skin.1

The Diagnostic and Statistical Manual of Mental Disorders, 5th ed., classifies delusional infestation as a somatic-type delusional disorder.1-3 What the patient experiences is a very real, persistent, and disruptive sensation on or in the skin regardless of the use of home remedies, pesticide treatments, or sanitation of the area perceived to be infested.4 Patients typically put a great deal of energy and time into proving the existence of a parasite or pest while denying any suggestion that their experience is a psychiatric condition.4-6

Because of its fixed nature, the delusion presents significant challenges to healthcare providers, but it can be treated. This article describes signs and symptoms, available treatments, and appropriate nursing interventions.

Unshakable conviction

The presence of an unshakable conviction of infestation is a hallmark of delusional infestation. Patients typically complain of invisible skin parasites or other organisms with accompanying pruritus. However, upon expert assessment, no such organisms can be found.

Skin assessment may reveal multiple areas of irritation or injury due to chronic scratching, frequent cleaning, or repeated chemical treatments. Some patients may even attempt to cut out the source of the uncomfortable sensations. In addition, the nurse may see scarring from previous efforts to treat the perceived problem.4,5 Patients may blame the perceived infestation on exposure to an unclean environment or person.2,5

Patients often become desperate to find what is causing the discomfort and will go from one professional to another in an effort to validate, confirm, and find treatment for their perceived infestation.5 Among the professionals patients may seek out for consultation are healthcare providers such as primary care practitioners, dermatologists, and allergists, as well as insect experts such as entomologists and pest control technicians.6-9

Patients will often exhaustively harvest, catalog, and submit samples to healthcare providers in a behavior often referred to as the “specimen sign.”2,6,10,11 These specimens can include skin cells, scabs, hairs, plants, dust, and photographs of skin lesions.2,6

Failure to obtain relief from over-the-counter or prescribed medications may drive patients to apply unconventional and sometimes highly toxic compounds to the body in an attempt to alleviate symptoms. Patients may also ask a local pest control company to treat inside the home to eradicate the unseen pest. Some people have been known to spray over-the-counter pesticides on themselves or ask a pest control professional to spray them with commercial pesticide, which is not legal. Neither of these actions is safe and may lead to deepening of the delusion as well as skin irritations and other health problems from pesticide exposure.7

Assessment and diagnosis

The healthcare provider will perform a thorough physical and psychosocial assessment to determine if the patient has the primary or the secondary form of the disorder. A patient with primary delusional infestation, the focus of this article, has no identifiable infestation or any other recognized cause for the uncomfortable skin sensations.6,11 (See Risk factors for primary delusional infestation.) Secondary delusional infestation results from a known medical or psychiatric condition or behavior that causes the uncomfortable skin sensation and that may be treatable.6 Examples of such underlying conditions include illicit drug use, topical exposure to chemicals, allergies, anemia, cancer, diabetes, lupus, schizophrenia, cirrhosis, and dementia.6,8,9,10

Before making a diagnosis of delusional infestation, the healthcare provider must consider whether the patient actually has an infestation of a biting organism. Some entomologic causes of skin irritation include infestation with or bites from bed bugs, spiders, head lice, fleas, mites, and mosquitoes.7,9 Each person's skin reacts differently to arthropod bites or stings; therefore, it is not possible to accurately diagnose the cause of a bite, bump, rash, or welt simply from assessing the lesion. The healthcare provider should submit any necessary specimens to appropriate experts to assist in diagnosis and treatment.9 For example, proper evaluation of a specimen by an entomologist may be helpful to confirm or rule out the presence of living organisms such as insects, spiders, or mites.12

The healthcare provider will also need to carefully review the patient's current medications. Even if polypharmacy is not a factor, the provider must rule out an adverse reaction to one of the patient's regular medications as a cause of symptoms. For example, pruritus is a common adverse reaction to many medications such as opioids, psychotropic drugs, and some antibiotics.

The initial nursing priority is to conduct a thorough physical and psychosocial assessment while building the foundation of a therapeutic relationship. The nurse should examine the skin closely for signs of injury or infection associated with scratching or previous efforts at self-treatment. When performing medication reconciliation, the nurse should obtain a detailed history of medications, chemicals, or other interventions that the patient may have used prior to the present encounter.

Treatment options

After the provider rules out a true infestation and if a secondary cause cannot be identified, the diagnosis of primary delusional infestation can be made. The healthcare team and patient then must work together to develop a plan of care. Management of the disorder must be interdisciplinary, holistic, and patient-centered.11 Patients tend to reject, at least initially, any evidentiary data that run counter to their conviction, and challenging their delusion may lead them to resist treatment or abandon care altogether.8,13 When developing a treatment plan, nurses and other healthcare professionals should take care to emphasize symptom reduction and emotional well-being rather than attempting to refute the delusion by overpowering the patient with scientific evidence or dwelling on the likelihood that the disorder is psychogenic in nature.

First-line pharmacologic treatment for primary delusional infestation is currently a low-dose, second-generation atypical antipsychotic such as olanzapine or risperidone.5 These drugs are generally considered to be safe and well-tolerated.10 Studies indicate that their effectiveness in achieving remission ranges from 60% to 100%, depending on the drug.5

Providers should stress the potentially beneficial secondary effects of antipsychotic therapy to mitigate patient resistance to initiating a psychiatric medication. For example, providers can educate patients that in addition to reducing the feeling of the perceived infestation, the medication may also reduce anxiety and improve sleep.4 Long-acting, injectable antipsychotic formulations are available and may help patients adhere to therapy over time.6 Depending on the patient's clinical condition, other complementary medications may be prescribed for palliative effect, such as antihistamines, steroid creams, or topical emollients.5

Cognitive behavioral therapy (CBT), in concert with medication, can round out the treatment plan. Ideally, CBT will allow patients a safe space to begin to question or redirect their delusional thoughts while promoting positive coping skills.5,10 CBT may also help counter depression, which often accompanies delusional infestation.10

Nursing interventions and support

Nursing care for patients with delusional infestation consists primarily of providing emotional and palliative support. The nurse can also act as a patient advocate and care coordinator within the interdisciplinary team.11 The nurse should convey to patients that relief is possible and encourage them to work with their care provider rather than seeking advice in online forums or attempting to self-treat with inappropriate over-the-counter treatments, home remedies, or household pesticides.

The nurse should recognize that patients may distance themselves from friends and family for fear of passing an infestation to others. In addition, because the disorder consumes their thoughts, they may have difficulty with conversation and abandon relationships.11 Proper nursing care and support can help prevent these patients from moving further into social isolation and deepening the fixation. All care providers can help patients identify goals and set short-term objectives aimed at emotional relief and symptom reduction.

Therapeutic communication is a nurse's most valuable tool in caring for someone with delusional infestation. It is important to avoid either affirming or denying the delusion; instead, employ nonverbal cues, such as sitting close while conversing to project confidence that the patient is not infested or contagious.5

When speaking with a patient, the nurse needs to control the direction of the conversation.5 For example, the nurse should allow only brief discussion of the delusion during any given visit before shifting focus to strategies for achieving relief and remission. The patient may benefit from discussing sources of stress and brainstorming techniques to reduce or cope with the stressor.3,5

CBT, provided by a nurse trained in this technique, is another strategy that can decrease the severity of the delusion.14 Establishing trust and rapport between nurse and patient facilitates earlier diagnosis and treatment, and may improve outcomes by reducing the risk of injury and infection caused by incessant scratching and picking.

If a provider prescribes an atypical antipsychotic such as risperidone or olanzapine to treat delusional infestation, nursing care must include careful teaching regarding expected benefits and possible adverse reactions. Nurses should also regularly assess for potential complications associated with antipsychotic medications, including elevated blood glucose levels, weight gain, and hyperlipidemia.11,7

Inform patients that the medication may take time to reach a therapeutic level in the body. Instruct patients to continue taking the prescribed medication as directed by the healthcare provider, even if symptoms seem to have subsided, as this is a sign the medication is working. Inform patients that pharmacotherapy may not be fully effective for several weeks or months after initiation of treatment.10

It is also important to educate patients not to stop taking their prescribed medication abruptly. If they experience troublesome adverse reactions, they should instead notify the healthcare provider, who may modify the treatment plan.

Nurses are in an ideal position to provide educational resources to the community about delusional infestation. Even pest control professionals may benefit from information on the condition and welcome resources for customers seeking initial or repeated visits for unverifiable pests.

Nurses can also raise awareness of the disorder among healthcare providers and model nonjudgmental, empathetic care that stresses the importance of early diagnosis to mitigate self-harm and to reduce the incidence of further negative psychological effects from the condition.

Risk factors for primary delusional infestation

Age is a leading risk factor for delusional infestation. The prevalence peaks moderately during young adulthood, at which time cases are most commonly correlated with drug use—particularly use of cocaine, methamphetamines, and opioids.8 Some evidence suggests that cases peak again among the middle-aged, with an average patient age of 57.15 Other research suggests that delusional infestation is predominantly a disease of middle-aged and older adults and may correlate with age-related neurodegeneration.3

Gender is another risk factor, with female patients outnumbering males at a rate of nearly 3:1.11,15 Prolonged exposure to a person afflicted with delusional infestation may put some people at risk for developing the delusion themselves, a phenomenon known as folie à deux.5 This generally occurs in cases where family or friends are living with the affected person. This phenomenon is seen predominantly in females as well.5

Delusional infestation may correlate with social isolation coupled with a high degree of online interaction, which can create an echo-chamber effect that reinforces the delusion and leads to more unhealthy behaviors.5 Stressors such as divorce, loss of income, and other major life changes may trigger onset of the delusion.8


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CBT; cognitive behavioral therapy; delusional disorders; delusional infestation; pruritis

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