Background: Nonattendance is common among patients suffering from delusional infestation (DI) with a risk factor for poorer patient outcomes. Objective: The aim of this study was to determine the incidence rate and predictors of nonattendance among patients presenting to a psychodermatology department with DI and the subsequent effect on the success of prescribing new antipsychotics. Methods: Data of 265 patients were reviewed of the Amsterdam UMC, the Erasmus University Medical Center, the Royal London Hospital, and the Liverpool School of Tropical Medicine between January 2008 and October 2019. Results: We observed that among the patients who attended the first consultation, 57% (n = 144) did not attend their second visit. Recreational drug use was significantly higher in the nonattendance group compared to the attendance group (25% against 18%). Patients who had a history of previously prescribed antipsychotics at the time of the first consultation were less likely to get prescribed antipsychotics from the psychodermatology departments for DI; however, prescribing antipsychotic drugs by the psychodermatology department did not influence nonattendance significantly. Conclusions: People suffering from DI are at high risk of nonattendance, even in specialist settings. Patients with current illicit drug use and younger patients are particularly at risk of this.

© 2022 The Author(s). Published by S. Karger AG, Basel

Introduction

Delusional infestation (DI) is a psychiatric disorder in which patients have the fixed belief that they are infested by living or nonliving pathogens that damage their skin, other organs, or their environment [1-4]. It causes a variety of uppermost dermatological and physical symptoms ranging from the fixed belief of being bitten by pathogens such as mites or parasites, an itchy feeling on the skin, to the conviction of being completely infected in all organs. These symptoms occur without any medical or microbiological evidence of a true infestation [5]. It is primarily a psychiatric disease, but patients usually seek care from dermatologists. DI can arise de novo or can present secondarily as a result of an underlying physical, neurological, or psychiatric disease or as a consequence of prescribed or illicit drug use [5]. The prevalence can only be estimated. Population-based studies found an incidence of DI of 1.9 cases (95% CI: 1.5–2.4) per 100,000 person-years and a prevalence of 27.3 per 100,000 person-years [6]. Within psychiatry, DI is diagnosed as a delusional disorder in ICD 11 and a somatic delusional disorder in Diagnostic and Statistical Manual of Mental Disorders, fifth edition.

Patients with DI usually do not seek care from health professionals. If they do, they present mostly to general practitioners, dermatologists, tropical medicine, or other somatic health practitioners but not to psychiatrists [7]. They believe their condition to be purely cutaneous (or physical), and it is often a real challenge to educate them about the psychiatric background of their symptoms and engage them in treatment. Patients often refuse referral to a psychiatrist and nonattendance after prescribing antipsychotics is described [8].

In primary care, nearly 20% of patients do not attend more than two appointments [9]. This corresponds to percentages described in dermatological practice [10]. Nonattendance has also been described in psychiatric patients, and percentages up to 60% for psychotic disorders have been reported. Reasons for nonattendance in this population are cognitive reasons, i.e., misconceptions about the disorder and its treatment, disagreement with the diagnosis, or dissatisfaction with the prescribed treatment [11].

The treatment of choice in DI is an antipsychotic as antipsychotics are effective and safe. There are no randomized clinical trials of antipsychotic medication for primary DI except for one very small study published in the 1980s [12]. A review of published case series and observational trials involving approximately 100 patients with DI found response rates for antipsychotics of 60–100 percent [13]. In the past, treatment for patients with DI has been pimozide [14]. However, in recent years, other second generation antipsychotics with a better safety profile are preferred [15].

Despite the fact that DI is a somatic delusional disorder, patients may or may not have had treatment with antipsychotic drugs or other psychotropic medication by former healthcare providers [5]. To our knowledge, a retrospective study of psychotropic use in DI patients does not exist. In this study, we aimed to determine.

a. the risk of nonattendance

b. the percentage of patients presenting to a psychodermatology department with DI who have been treated elsewhere with antipsychotics and

c. the subsequent effect on the success of prescribing new antipsychotics

Methods

This retrospective observational study included patients who attended the specialist psychodermatology departments in the Amsterdam UMC, the Erasmus University Medical Center, the Royal London Hospital, and the Liverpool School of Tropical Medicine between January 2008 and October 2019. The need for informed consent was waived by the Medical Research Ethics Committee, Amsterdam UMC. All patients diagnosed with DI at the participating psychodermatology departments were included; there were no exclusion criteria. Data of 265 patients were analyzed; 14 patients were excluded due to missing data or different diagnoses.

Data were obtained using patient files and included patients’ characteristics, psychiatric history, previous prescribed antipsychotic drugs, duration of symptoms of DI at the time of first consultation, and outcomes at the psychodermatology departments (Table 1). For statistical analysis, IBM Statistical Package for Social Sciences software version 25 was used. For patient characteristics and presentation details, the mean, standard deviation, and percentages were calculated. The χ2 test, unpaired t test, and Mann-Whitney U test were performed to determine whether there is a statistically significant difference between our outcome variables. A p value of 0.05 or less was defined as statistically significant.

Table 1.Results

The data of 251 patients were analyzed. The mean age was 58 years with a range of 23–97 years. 37% (n = 93) of the patients were male. 34% of the patients (n = 84) had a known psychiatric disease at the time of or prior to the first consultation. In 24% of the patients (n = 61), this information was not available. The psychiatric diagnoses included depression, schizophrenia, and psychosis. Six percent (n = 16) of patients had been diagnosed before with DI. Sixteen percent (n = 39) of patients had used an antipsychotic drug, prescribed by a physician.

The median duration of the DI symptoms was 24 months. Of the patients who attended the first consultation, 57% (n = 144) were lost to follow-up, consisting of patients who refused all treatment, patients who started initial treatment but refused further treatment, and patients that did not appear at their next appointment without giving a reason.

Consequently, 41% (n = 104) of patients were not lost to follow-up. These included patients who were discharged because they were now asymptomatic or had a good response to therapy, patients who are still in follow-up, and patients whose treatment was taken over by another physician or institute, for example, one which was closer to home or a psychiatrist. Of those not lost to follow-up, 1 patient died, 1 patient did not respond to any treatment, and 1 patient was lost to follow-up for an unknown reason.

Nonattendance

In the patient nonattendance group, the mean age was 4 years younger, and there were relatively more male patients (43% compared to 29%). Between the nonattendance group and the attendance group, there was no significant difference regarding the history of psychiatric disease and previous prescribed antipsychotic drug use (Table 2). In contrast, recreational drug use was significantly higher in the nonattendance group (25% against 18%). Duration of symptoms of DI was longer in the nonattendance group, but this was not statistically significant. Furthermore, prescribing antipsychotic drugs by the psychodermatology department did not influence attendance significantly.

Table 2.

Differences between groups of nonattendance

Duration of Follow-Up

In the nonattendance group, the mean duration of follow-up was 47 weeks, with an SD of 72 weeks. However, 16% (n = 41) of the entire study group did not even attend their second appointment.

Prescribing Antipsychotic Drugs

During treatment at the psychodermatology department, 78% (n = 195) of patients were prescribed an antipsychotic drug at some point during their treatment, mainly including risperidone, amisulpride, and olanzapine (Table 3). Patients who had a history of previously prescribed antipsychotics at the time of the first consultation were less likely to get prescribed antipsychotics from the psychodermatology departments for DI. In this group, 25% of the patients refused antipsychotic drugs.

Table 3.

Prescribing antipsychotic drugs

Discussion

DI is a therapeutically challenging disease in which there is a considerable chance that the patient will not comply with follow-up appointments for various reasons. In particular, the lack of patient’s understanding of the disease makes it difficult for them to accept a suitable therapy. There is therefore a significant chance that the patient will not engage and may not appear on the next outpatient appointment [16]. In our sample, 57% of patients withdrew from follow-up at some point. 16% were lost to follow-up after their first appointment. These data confirm that there is a relatively high risk that patients will withdraw from care at some point. One risk factor we have identified is previous or current substance drug use. Substance drug use is a well-known comorbidity in DI [17]. In our sample, there was a high substance drug use, 22% (n = 56) compared to 30% (n = 76) no drug use and 47% unknown (n = 119). It is therefore important to ascertain from the patient whether they have current harmful drug use. Another factor is younger age, which is independently associated with higher nonattendance. Specific efforts should be made to engage younger patients to reduce this risk.

We already know that a longer period of untreated DI can lead to both loss of efficacy in any further treatment and loss of engagement with healthcare professionals [18]. So, we have shown that being lost to follow-up is a further risk for the patient. Suffering increases along with dangerous attempts to rid themselves of the alleged pathogens. In the worst cases, those afflicted attempt suicide [19]. Hence it is very important to be aware of this risk and to try to motivate patients to engage with treatment. Treating physicians need to take into account factors that can increase the risk of staying away. Patients with DI want their complaints to be taken seriously, and they want to understand where they come from. Communication and building trust therefore plays a pivotal role.

A good starting point is the thorough exploration of the complaints, with attention to all dimensions of those complaints, including thoughts about the infestation, emotions resulting from the symptoms, behavior and social consequences. This shows that the physician has understood the complaint and understands the patient’s problems holistically. The physician thus adopts an empathetic attitude, which helps to build up trust and engagement. It is important to remember that the patient’s symptoms are real; what differs is the belief of the underlying pathology. Another advantage of such thorough exploration is that potential biopsychosocial problems are more likely to surface and that further questioning is easier. This thorough exploration is necessary to justify the use of “delusional infestation” or similar terms as a working hypothesis and to take it as a starting point for the subsequent treatment plan.

The second important point is to offer an explanation that makes sense to both the physician and the patient. For example, alternative explanatory models for the itch that the patient experiences can be given to give space for an alternative origin of the complaints. Antipsychotics are the cornerstone of therapy. However, given the patient’s nonpsychiatric understanding of the disease, it is often difficult to motivate the patient to try this. Explanatory models can facilitate this difficult conversation [20].

Third, expressing positive expectations are important. These include the prospect that

a. the complaints can decrease

b. the consequences of the patient’s complaints can be contained

c. the patient can function better and have a normal life again

Many physicians may be unaware of the positive effect this can have but may also be wary of expressing such expectations if they do not know whether it is warranted. If the doctor expresses a positive expectation about the course of the illness, this can have a positive effect on patient engagement. Furthermore, positive outcomes are likely if patients take medication regularly because antipsychotics have a high efficacy.

Last but not least, our study reveals that patients who had antipsychotics prescribed in the past are less likely to be treated with antipsychotics in the participating specialist clinics. The cause of this is not quite clear, but hypothetically, there are several explanations. First, it may be that previous antipsychotic therapy has not reduced the complaints or that the response was minimal. It is therefore good to mention during the consultation that it is always useful to switch to another antipsychotic if the former drug has not helped. Side effects of antipsychotics can also affect compliance. It is advisable to ask about and take into account previous side effects. Second, the lack of insight into the disease can hinder treatment with antipsychotics. This point is perhaps the most challenging for the physician – good motivational conversation techniques are essential.

It is worth mentioning that there are several confounding factors to appoint, including diversity in age, differences in population personality, and duration of delusional disorder. This makes it statistically difficult to assess to what extent the factors recreational drugs, age, and nonattendance are independent of each other. Thus, these findings should be interpreted with these limitations in mind. However, so little has been published about DI that all the information collected about it contributes to a better understanding of the disease and thus hopefully to better treatment.

Conclusions

People suffering from DI are at high risk of being lost to follow-up, even in specialist settings. Patients with current illicit drug use and younger patients are particularly at risk of this. Moreover, this study shows that it becomes more difficult to initiate effective medication if patients have already received antipsychotics from another healthcare provider in the past.

Key Message

People suffering from DI are at high risk of nonattendance.

Acknowledgements

We thank Stephen Bertel Squire, School of Tropical Medicine, Liverpool for his valuable suggestions on the manuscript.

Statement of Ethics

This study did not fall under the scope of the Medical Research Involving Human Subjects Act, as confirmed by the local Medical Research Ethics Committee. The need for informed consent was waived by the Medical Research Ethics Committee, Amsterdam.

Conflict of Interest Statement

The authors have no conflicts of interest to declare.

Funding Sources

No funding was received for this study.

Author Contributions

Patrick Kemperman designed the study. Mèdelyn Wennekers, Sara Aboalkaz, and Ahmed Kazmi collected all the data. Mèdelyn Wennekers performed the data analysis. Patrick Kemperman and Mèdelyn Wennekers wrote the manuscript. Patrick Kemperman, Peter Lepping, Anthony Bewley, and Rick Waalboer-Spuij supervised the multicenter study. All the authors critically commented on the manuscript.

Data Availability Statement

All data generated or analyzed during this study are included in this article.

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