Delusional infestation by proxy — What should veterinarians do?

Delusional Infestation (DI), also termed Ekbom’s Syndrome or delusional parasitosis, is a psychiatric disorder that manifests as an unshakable false belief of being infested with living or inanimate pathogens. The chief complaint of patients with DI is a rigid belief against all medical evidence that they are infested. Approximately 40% of reported cases are due to a primary psychosis, while the remaining 60% are secondary to neurologic or other psychiatric disorders, side effects of medications, substance abuse, or other metabolic diseases (1).

Most commonly, DI manifests as a mono-delusional disorder, where only the patient experiences the delusion on their body. However, variants of this disorder exist, including a shared delusion (also known as folie à deux), in which more than one person believe themselves to be infested, and DI by proxy (DIP), in which the patient projects the delusion onto a third party who usually cannot share the delusion (e.g., a pet, a young child, or a mentally disabled person) (1). Recently, we proposed a third variant, termed a double delusional infestation (DDI) (2), in which the patient believes that both they, and a third party who cannot share the delusion, are infested.

There are sporadic case reports of DIP, in which the delusion was projected onto a pet or a child (3–6). Authors have suggested that this is a “rare” manifestation of DI (7). However, recently, we examined this phenomenon via a survey of veterinarians, and identified over 700 cases in which the veterinarian was reasonably convinced that the client was suffering DIP or DDI (2). Thus, from this study, it appears that the disorder, while relatively uncommon in everyday veterinary practice, occurs frequently enough to be of concern to the clinician. Furthermore, because the projection is onto a pet, the client is unlikely to present to a physician or be referred for psychiatric evaluation, explaining the apparent “rarity” of the condition in the medical psychiatric literature.

In our study, we examined the courses of action taken by the clinician, both in the initial diagnosis, and in any recommendations that they made by means of a survey amongst 724 veterinarians from several countries (mainly the US and Canada) recruited via the Veterinary Information Network (VIN, www.vin.com) (2). Furthermore, we identified frustration in many of the respondents in not knowing what should or should not be done with clients presenting with suspected DIP.

Therefore, based on this study, we have now attempted to provide veterinarians with some guidelines that might assist them in dealing with clients in whom they suspect DIP or DDI.

Client characteristics/demographics

Delusional infestation is more common in women than men. The average age of onset is 61.4 y (range: 9 to 92 y) in a prevalence study from the US (8), confirming findings from a bigger but older study from Germany (9). However, in our study of DIP in pets, middle-aged women (30 to 60 y) were most commonly identified (2). This might simply reflect the pet-owning population, rather than a different distribution of patients. On the other hand, similar to previous studies, over 75% of the cases we identified involved women. Most persons belonged to the middle classes (74%); however, we failed to find an association with socioeconomic status.

In 75% of the cases (252 out of 337) where data were available, the client claimed to be affected along with their pet (DDI). Of these, 53% showed the veterinarian lesions on their own bodies. In a small percentage of cases, the veterinarian identified lesions on a client who did not claim to be infested, that they considered consistent with DI.

Thus, our study suggests that in many cases of DIP, the delusion is projected by the client onto both themselves and their pet (DDI). Consequently, a veterinarian suspecting DIP should examine the client for evidence of self-trauma. Where possible, the clinician should also ask the client if they themselves or others within their personal environment believe themselves to be infested, or just the pet — since many parasitic diseases are zoonotic. Such questioning is generally reasonable when evaluating the pet. If the client states that they believe themselves to be infested, the clinician can ask to see lesions. The distribution of self-trauma in patients with DI classically involves areas that are easy to reach and scratch and these self-inflicted lesions are usually on the side of the body opposite to the dominant hand. Therefore, commonly, the middle of the back will be devoid of such lesions. Such a pattern of distribution can help confirm the suspicion of DIP or DDI.

Patient characteristics

Dogs and cats represented the most common pets presented with DIP (87%). This likely reflects the general demographics of small animal clinicians who responded to the survey. In most cases, an unidentified ectoparasite was the alleged “infesting” organism, with some clients claiming to have seen “worms” (endoparasites). Approximately 50% of the clients identified “lesions” on the pet that they claimed were associated with the infestation. However, in only about 25% of these cases did the clinician confirm that a lesion was present.

Approximately half of the pets had been treated by the client in some manner prior to presentation. Approximately 2/3 of the clients presented material that they claimed contained the infesting organism. This is akin to the “specimen sign” seen in DI and slightly more common than in DI which is not by proxy. Many survey respondents noted that the clients had consulted multiple veterinarians for the problem prior to visiting them. This trend of seeking multiple consultations is similar to that experienced by physicians dealing with patients suffering from DI — many patients will consult multiple physicians prior to being referred for psychiatric evaluation.

Thus, based on our study, the pets presented to clinicians infrequently have lesions. However, clients frequently present material that they claim is the infesting organism.

The initial approach to the client with suspected delusional infestation — Look for the pathogen!

Delusional infestation is usually suspected after a fruitless, but reasonably comprehensive, investigation for a pathogen. Most clinicians in our study performed a battery of diagnostic tests, including physical examination, dermatophyte culture, or Wood’s Lamp examination, combing for flea dirt, adhesive tape test for Cheyletiella (in feline patients), skin scraping (for mites), fecal examination (for endoparasites). If a sample had been presented by the client for inspection, clinicians generally either examined the sample under a microscope (or dissecting microscope), or submitted the sample to a diagnostic parasitologist for evaluation.

Such actions by the clinician are warranted and encouraged. Good-faith attempts to identify the pathogen should be performed. Indeed, in our study, clinicians identified an organism in 25 cases (but did not necessarily attribute the clinical signs to the organism). It is perfectly conceivable that the client is not delusional, but that the patient is, in fact, infested. Consequently, ruling out a true infestation is always warranted.

The attempt to identify a pathogen also strengthens the client-veterinarian relationship. Several survey respondents commented that the clients felt relieved that the clinician “took them seriously” and considered the infestation to be plausible at the outset. This increased trust of the client can help the clinician to later provide the most appropriate advice or help for the client, once the DI is strongly suspected. This is in keeping with strategies employed by DI clinics. Tables 1 and 2 suggest questions for veterinarians to ask their clients.

Appendix 1.

How to approach suspected DI with patient. Suggested actions:

“Quote” the patient’s word and acknowledge his or her suffering to build up trust (e.g., “I can see you are afraid that your pet has an unknown infection…”) You may want to “agree to disagree;” this means you acknowledge that the pet owner has the right to have a different belief than you have, but claim that he or she shall acknowledge that you have the same right. Do not directly reinforce the pet owner’s (false) beliefs. Do not say “Yes, I found XY” (although you have not), or “Try this worm cure” (although there are no worms). Do not directly challenge the pet owner’s (false) beliefs. Do not say “The pet has nothing, settle down, it’s all in your head/psychological/ your fault” or “You are wrong. I know it better than you do, I am the professional/doctor.”

Appendix 2.

How to determine whether the pet owner believes the pet and others are infested. Suggested questions:

“Do you feel you are infested, too?” If they respond “yes,” you can ask to see the lesions. If they show you lesions, you can ask “Have you consulted a physician or a dermatologist about these?” If they answer “no,” this allows you to suggest a consultation between you and their physician to help explain the pet’s “problem.” If they answer “yes,” you can ask what was determined by the physician to help you diagnose their pet’s “problem.” If they do not show you lesions, look for evidence of self-trauma. If they respond “no,” proceed to the following questions. “Do you think your child(ren) are infested?” “Are there other people close to you who think they are infested or whom you think are infested (although doctors failed to find a pathogen)?”

You found no pathogen — Should you treat anyway?

Delusional infestation by proxy or DDI is suspected when the veterinarian fails to identify any evidence of infestation or pathogens despite reasonable (or exhaustive) attempts to do so. The diagnosis also rests on the descriptions of the symptoms, which are often improbable and unscientific. In our study, it became evident that approximately 50% of clinicians, after a series of negative diagnostic tests, prescribed some sort of therapy. Often, this was done “just in case I missed something,” or because “the pet could do with de-worming and ectoparasite control anyway,” or because “it would be unlikely to harm the pet, and might satisfy the client,” or “I might be able to demonstrate treatment failure to convince the client later.”

These are all completely understandable, rational justifications. Failure to identify a pathogen does not completely rule out the possibility of its existence (you cannot ever prove a negative). Furthermore, clinicians have learned that clients expect them to “do something,” and therefore, develop and reinforce a behavior pattern of providing treatments whenever possible, to keep the client satisfied.

However, any treatment directed against the apparent infestation has been shown to strengthen and reinforce the patient’s delusion, and validates the patient’s claim of infestation. In the case of DIP or DDI, this treatment of the pet, or the environment, would serve to similarly reinforce the delusion.

Therefore, despite the urge to treat the patient, the clinician should not offer any treatment directed against the apparent infestation and should strongly resist any attempts by the client to obtain treatment.

The other important issue relates to animal welfare. Just as futile and superfluous treatments are unethical and strongly discouraged in humans, principles of animal welfare suggest that the same is true for animals. No animal should undergo treatment purely for the benefit of the vet or the owner. Treatment, even when it is unlikely to cause harm, should always be directed at a treatable illness.

I think the client is delusional — What should I do?

Delusional infestation is an extremely frustrating and difficult-to-treat psychosis, because the patient cannot easily (or sometimes ever) be convinced that they are in fact imagining the infestation. Therefore, a veterinarian has little chance of convincing the client that their pet is not infested. Trying to do so will frustrate or anger the client, who is likely to seek veterinary advice elsewhere (as evidenced by our observation that many clients had consulted multiple veterinarians about the problem).

Since the veterinarian is not bound by “patient-doctor” confidentiality, the initial approach can be to consult with a family member of the client. Detailing the concern of the diagnosis of DIP to a family member can reveal valuable information (in some instances, family members admit that the client has been diagnosed with a psychiatric disorder, occasionally even with DI). For example, given the prevalence of secondary DI (induced by drugs, substance abuse, organic neurological disease, or metabolic disease), a veterinarian could enquire of the family member whether such disorders are possible in the client. Figure 1 exemplifies a pathway of action for veterinarians.

Figure 1.

Suggested approach for veterinarians confronted with a client suspected of suffering from delusional infestation by proxy or double delusional infestation.

The clinician can suggest to the family member that a consultation with a physician or a mental health professional is warranted. They can offer to provide the physician or psychiatrist with the evidence they used to formulate the hypothesis that the client suffers DI. This can help the physician address the problem more rapidly. Suggesting to the client directly that they should consult with a physician for a suspected DI is unlikely to be effective but depends on the trust that has been built between veterinarian and client and the degree of delusional intensity the client has.

If the client appears to suffer from DDI, an alternative can be to ask whether you, as a veterinarian, could talk to the client’s physician or family doctor. This can be done under the pretext that you would like to advise the physician of your concerns about the pet’s “infestation” and that you will be better able to convey this information directly. You can also suggest that the client should consult their physician about their own “infestation,” because you are not allowed to diagnose human medical conditions. If the client agrees, you can then explain your concerns to the physician confidentially to prepare her/him for further patient (client) evaluation. Suggestions to see a psychiatrist will only be effective if there is already a very trustful relationship between veterinarian and client and should never be attempted at first consultation. Such a referral is likely best handled by the client’s own physician.

Alternatively, if the client exhibits lesions consistent with DI on their body, then a suggestion to consult a dermatologist about their condition can be productive. Most dermatologists are familiar with DI as a potential cause of excoriated skin lesions. Such a suggestion is likely to be perceived as empathetic and unlikely to alienate the client.

Risk assessment

Clients with DI can use dangerous pesticides or bleach and other chemicals on themselves or the pet in the attempt to get rid of the alleged infestation. This can pose a significant risk to the client or the proxy (pet, children, other family member), especially when the proxy is unable to exercise a choice. A basic risk assessment is always required as DI is associated with the risk of significant harm. The main questions in any risk assessment are: Is there any reliable evidence of a substantial health risk to the pet, the pet owner, or his/her relatives secondary to the pet owner’s DI (e.g. feeding the pet with toxic amounts of anti-infective agents, causing severe skin rashes in a child because of unneeded skin cleaning measures)?

1. Who is at risk?

2. How immediate is the risk and therefore how urgent is it to act?

3. How significant is the potential danger?

4. Is there any obvious violation of local legislation (e.g., animal protection laws, child abuse)?

If any of the above is the case, you not only offer help, but you must take action. Depending on who is at risk [pet owner, other adult, child(ren) or animal] you must contact the appropriate local or federal authority or institution. This may be the police, a public health department, Child Protection Services, a community mental health team/social workers, or the state/ provincial veterinary office, or animal welfare groups to discuss appropriate measures that comply with local legislation (e.g., removal of custody of children from their parents, involuntary admission to a psychiatric hospital, removal of the animal). In countries like the UK any clinician is obliged by law to alert children’s services if any child is found to be at significant risk.

Conclusions

Delusional infestation by proxy (or double delusional infestation) is a condition that many practicing veterinarians are likely to experience at least once in their professional career. It is exasperating and frustrating to both the client and clinician. Veterinarians should make good-faith attempts at ruling out pathogens. If, after such a series of diagnostic investigations, they believe the client suffers DI, they should avoid providing any treatment for the pet’s apparent condition, but should make attempts to obtain professional medical help for the client. Often, this can be done by consulting with family members or with the client’s physician.

Appendix 3.

How to determine whether the pet owner likely suffers from DI by proxy or double delusion. Suggested questions:

“Have you seen any other veterinarians about this problem in your pet?” If they respond “yes,” you can ask what the outcomes of those visits were “Have you attempted any treatment of the condition, or has it been prescribed by any veterinarian previously?” “Do you have any samples of the parasitic organism that we can analyze or examine?” “Does your pet have any lesions (sores) that you attribute to the parasitic infestation?”