LEARNING OBJECTIVES

After reading this article you will be able to:

• • demonstrate an understanding of delusional infestation and the interface with different specialties

• • understand the approach to take with patients with delusional infestation

• • demonstrate knowledge of available treatment options.

Most human beings have a fear of infestation and parasites, in large part because they are associated with uncleanliness and shame. In some individuals, this fear persists despite the lack of objective evidence of infestation. The belief may be sustained with a variable degree of conviction, spanning from non-delusional (obsessional thoughts) to delusional thinking, and it is termed delusional parasitosis or delusional infestation (Freudenmann Reference Freudenmann and Lepping2009). Delusional infestation has been of interest to a range of professionals, including entomologists (Hinkle Reference Hinkle2011; Pradhan Reference Pradhan, Saikia and Borkakati2019), zoologists (Trabert Reference Trabert1995) and dermatologists (Lyell Reference Lyell1983; Bewley Reference Bewley, Lepping and Freudenmann2010). The reluctance of people with delusional infestation to see psychiatrists, owing to various factors, including stigma of mental illness and lack of insight, is widely reported in the literature (Freudenmann Reference Freudenmann and Lepping2009). Psychodermatology clinics aim to provide neutral settings for consultation to address the problem of non-engagement among people with delusional infestation (Aguilar-Duran Reference Aguilar-Duran, Ahmed and Taylor2014), but there is a need to develop disease-specific pathways in primary care and hospital settings, where the majority of patients seek help.

Scope of the problem

Delusional infestation is considered to be a rare disorder, particularly by psychiatrists (Freudenmann Reference Freudenmann and Lepping2009). A population-based study in Minnesota, USA, reported an incidence of delusional infestation of 1.9 per 100 000 person-years (Bailey Reference Bailey, Anderson and Lowe2014). The incidence increases with age, with the highest incidence between 50 and 80 years of age (Lyell Reference Lyell1983; Trabert Reference Trabert1995). The female:male ratio is estimated to be 1:1 until the age of 50 and 3:1 for people over 50 (Lyell Reference Lyell1983). In Germany, Trabert (Reference Trabert1993) (cited in Freudenmann Reference Freudenmann and Lepping2009) reported a prevalence of 5.58 per million population based on cases reported to hospitals and public health services and a much higher prevalence, of 83.23 per million, based on a survey of private practices. A survey of entomologists in the USA estimated that around 100 000–250 000 Americans had delusional infestation (Hinkle Reference Hinkle2011). Point prevalence in a UK dermatology clinic was reported at 1.48 per million (Lepping Reference Lepping, Baker and Freudenmann2010).

Individuals cause great suffering to themselves and their families because of their preoccupation with symptoms and the obsessionality of the condition (Freudenmann Reference Freudenmann and Lepping2009). Multiple medical consultations and use of several laboratory, microbiology and diagnostic services add to the significant costs and economic burden for healthcare services (Boggild Reference Boggild, Nicks and Yen2010). It is estimated that 8–14% of people with delusional infestation have a family member or close friend affected with similar symptoms, which has been termed shared psychotic disorder (Freudenmann Reference Freudenmann and Lepping2009).

Diagnostic considerations

The majority of people with delusional infestation do not present to psychiatrists (Foster Reference Foster, Hylwa and Bury2012). Instead, they present to general practitioners, dermatologists, physicians, otolaryngologists and/or ophthalmologists with complaints of infestation of the skin and/or different parts of the body, including the ear, eye and gastrointestinal tract, wanting the alleged organisms to be identified and eliminated (Moriarty Reference Moriarty, Alam and Kalus2019). When tests proved negative, patients continue to demand more investigations to validate their beliefs. Patients’ reluctance to accept the lack of infestation should alert professionals to the possibility of delusional infestation.

Freudenmann & Lepping (Reference Freudenmann and Lepping2009) proposed two criteria for the diagnosis of delusional infestation: (a) patients have the conviction of being infested by animate or inanimate pathogens without any medical or microbiological evidence of a true infestation; and (b) they have abnormal cutaneous sensations explained by the first criterion. Delusional infestation is included in ICD-11 (World Health Organization 2018) and DSM-5 (American Psychiatric Association 2013) as a delusional disorder with a fixed, false belief that persists for at least 3 and 1 month, respectively. The delusion of infestation is encapsulated without extension of delusional beliefs into other areas of life. The patient may have tactile, visual or auditory hallucinations related to the delusion itself but does not have other psychotic features meeting the criteria for schizophrenia (DSM-5).

Box 1 outlines the diagnostic steps and possible investigations to undertake with patients presenting with suspected delusional infestation.

Physical and psychiatric comorbidities

It has been estimated that around 60% of people with delusional infestation have an underlying organic or psychiatric condition (Trabert Reference Trabert1995), termed secondary organic delusional infestation or secondary functional delusional infestation (Freudenmann Reference Freudenmann and Lepping2009). Predisposing factors are shown in Box 2 and conditions associated with secondary organic or functional delusional infestation are listed in Table 1.

TABLE 1 Conditions associated with delusional infestation

Source: adapted from Al-Imam & Al-Shalchi (Reference Al-Imam and Al-Shalchi2019), Driscoll et al (Reference Driscoll, Rothe and Grant-Kels1993), Freudenmann & Lepping (Reference Freudenmann and Lepping2009), Pradhan et al (Reference Pradhan, Saikia and Borkakati2019) and Moriarty et al (Reference Moriarty, Alam and Kalus2019).

Substance misuse is more common in younger patients with delusional infestation, who might use substances to relieve the distress associated with their condition. An international study of the prevalence of substance use in delusional infestation reported that 30% of people with delusional infestation in specialised psychodermatology clinics tested positive for hard or soft drugs, most commonly amphetamines and cannabis (Lepping Reference Lepping, Noorthoorn and Kemperman2017).

Delusional infestation has a significant impact on quality of life, with increased distress, frustration and comorbid depression; it is also associated with increased suicide risk, which necessitates a thorough risk assessment on an individual basis (Freudenmann Reference Freudenmann and Lepping2009). A study of psychiatric comorbidity in 134 people with delusional infestation at a psychodermatology clinic in England found that 52% patients had anxiety, 41.6% depression and 49% appearance-related concerns (Shah Reference Shah, Taylor and Bewley2017). A retrospective study of patients with delusional infestation in a tertiary care academic medical centre in Minnesota demonstrated depressive disorders in 24%, anxiety disorders in 19%, drug use disorders in 19% and personality disorders in 4% (Foster Reference Foster, Hylwa and Bury2012).

Interface between psychiatrists and other professionals

The most commonly reported area of infestation is the skin on the hands, arms, lower legs and feet, although other parts of the body can be affected. Patients commonly see dermatologists because of their preoccupation with their skin complaints, but many dermatologists are not fully prepared to identify and treat this condition (Szepietowski Reference Szepietowski, Salomon and Hrehorów2007). The primary role of dermatologists is to exclude organic skin disease and treat any skin lesions arising as a result of self-treatment (e.g. dermatitis due to the use of chemicals) but it is not to offer psychiatric treatment.

Patients with delusional infestation can be a challenge for dermatologists, given that no infestation is found, even after repeated or specialised investigations and negative skin biopsies (Hylwa Reference Hylwa, Bury and Davis2011). Patients often refuse a psychiatric referral or any psychiatric treatment, but some dermatologists might be comfortable initiating treatment with psychotropic drugs, to avoid continued suffering for the patient (Winsten Reference Winsten1997). In a survey of 172 dermatologists in Poland, about 15% said they would prescribe medication such as anxiolytics or even antipsychotics for delusional infestation (Szepietowski Reference Szepietowski, Salomon and Hrehorów2007).

Up to a quarter of people with delusional infestation describe infestation with non-living pathogens (e.g. ‘fibres’, ‘filaments’) (Freudenmann Reference Freudenmann, Kölle and Schönfeldt-lecuona2010; Lepping Reference Lepping, Huber and Freudenmann2015). Apart from the skin, body orifices such as the nose, ear, mouth and anus may be affected, termed ‘orificial delusional infestation’ (Al-Imam Reference Al-Imam and Al-Shalchi2019). In some elderly patients, the whole gastrointestinal tract can be implicated (Freudenmann Reference Freudenmann and Lepping2009). Patients may report worms travelling in their gastrointestinal tract or through different orifices and seek help from a general physician or demand an endoscopy.

Most patients attempt to treat the infestation themselves, and some of these eradication attempts result in serious complications (Foster Reference Foster, Hylwa and Bury2012). Emergency physicians might be called to treat self-mutilation attempts by razor blades, nail-biting and purification rituals, such as applying insecticides that result in skin burns (Aw Reference Aw, Thong and Chan2004; Park Reference Park, Myers and Punekar2018). Presentation to other specialties has been reported in the literature, such as otolaryngology with self-inflicted trauma to the ear (Spariosu Reference Spariosu and Coira2015), ophthalmology with corneal damage (Meraj Reference Meraj, Din and Larsen2011) and urology with repeated urethral self-instrumentation and foreign body insertion, resulting in stricture formation (Ismail Reference Ismail and Cassidy2015). Some people with delusional infestation approach entomologists directly to investigate suspected organisms and a few demand frequent insecticide treatment of their homes by pest control organisations (Pradhan Reference Pradhan, Saikia and Borkakati2019).

Psychodermatology clinics

As mentioned above, treatment of delusional infestation (of the symptoms of the delusion) is challenging for dermatologists, particularly owing to patients’ reluctance to engage and accept the presence of a psychiatric or non-skin disorder (Ahmed Reference Ahmed and Bewley2013). Liaison between psychiatry and dermatology as a forum for exchange of insight and experience was identified almost a quarter of a century ago as a way forward for treating patients with this difficult and complex disorder (Winsten Reference Winsten1997). There are models proposed of psychodermatology clinics with access to a psychiatrist (Aguilar-Duran Reference Aguilar-Duran, Ahmed and Taylor2014) to treat people with delusional infestation. A psychodermatology clinic in the UK reported that over 70% of patients with delusional infestation were successfully treated by psychiatrists, dermatologists and psychologists working in collaboration (Healy Reference Healy, Taylor and Dhoat2009). A similar positive outcome (82% adherence to treatment) has been reported for people with delusional infestation treated in specialised multidisciplinary clinics in England, Italy and Russia (Romanov Reference Romanov, Lepping and Bewley2018). Early intervention models have been proposed, as longer duration of untreated psychosis is associated with significantly less favourable clinical outcomes (Romanov Reference Romanov, Lepping and Bewley2018).

Psychiatric management

Mental health professionals often have the challenging task of engaging with people with delusional infestation in non-psychiatric settings, as they are likely to refuse engagement in psychiatric clinics. Furthermore, despite the obvious presence of psychosis and the significant subjective distress, delusional infestation may not be classed as a severe and enduring mental illness and patients often do not meet the criteria for detention under the Mental Health Act 1983 to enforce any treatment (Freudenmann Reference Freudenmann and Lepping2009). However, in certain severe cases, where legally possible, detention under the Mental Health Act should be considered and attempts should be made to engage and educate patients about their condition and to discourage harmful self-treatments.

An integrative holistic approach with psychotropic medications, psychotherapeutic and sociotherapeutic methods may benefit up to two-thirds of patients, with improvements in delusional symptomatology (Sadock Reference Sadock, Sadock and Ruiz2017). A meta-analysis of 1223 cases conducted by Trabert (Reference Trabert1995) reported that about half of the patients attained full remission with psychopharmacological treatment. No particular strategy has been found to be superior to others and hence a consistent multidisciplinary approach is needed, with a combination of medications and psychological treatment.

Engagement

Non-engagement remains one of the major challenges, as a meaningful therapeutic alliance is often not established owing to the patient's conviction about the somatic nature of the illness (Lepping Reference Lepping, Russell and Freudenmann2007). This failure of the therapeutic alliance results from the obvious discrepancy between the patient's belief system and the clinician's ‘illness model’. Patients are reluctant to accept the mind–body link, focusing either on skin complaints or ‘infestation’ of the body. Professionals should focus on engagement, taking a non-judgemental attitude and conveying to the patient that their problems are being taken seriously (Koo Reference Koo and Lee2001). Clinicians should give the patient time to talk about their experiences, listening to their detailed stories and explanations about the alleged infestation (Sadock Reference Sadock, Sadock and Ruiz2017). Clinicians should be empathetic and acknowledge that the patient's symptoms are real; they should explore with the patient how the symptoms affect their lives, for example the associated social withdrawal and reduced activity (Freeman Reference Freeman2013). Clinicians should not challenge or confirm the patient's view about the cause of the symptoms early in the course of engagement (Silva Reference Silva, Kim and Hofmann2003).

Clinicians should find about the patient's expectations and agree realistic therapeutic goals in collaborative discussion (Freudenmann Reference Freudenmann and Lepping2009). Examples of goals could include reducing the distress associated with the delusions and improving quality of life; reducing skin lesions; reducing delusional conviction to a degree that enables normal social contact; increasing confidence; and re-engaging in activities (Freudenmann Reference Freudenmann and Lepping2009; Freeman Reference Freeman2013).

A Cochrane review on treatment for delusional infestation was unable to draw conclusions regarding the efficacy of any treatment (pharmacological or non-pharmacological) owing to the lack of evidence from randomised controlled trials (RCTs) comparing interventions with placebo (Assalman Reference Assalman, Ahmed and Alhajjar2019). Antipsychotics are the most commonly used medications for the disorder and most of the literature focuses on case series. A systematic review by Lepping et al (Reference Lepping, Russell and Freudenmann2007) of 16 trials and case reports demonstrated 60–100% partial or full remission rates with typical antipsychotics for primary delusional infestation, and rates did not differ significantly between typical and atypical antipsychotics. A further review by Freudenmann & Lepping (Reference Freudenmann and Lepping2009) recommended amisulpride, risperidone or olanzapine as first-line treatment and aripiprazole, quetiapine or haloperidol as second-line; however, the evidence of one agent being superior to another has come mainly from case series rather than RCTs. Ahmed & Bewley (Reference Ahmed and Bewley2013) studied adherence to treatment for delusional infestation in a psychodermatology clinic in the UK and concluded that patients’ adherence to physical health medications or skin treatment was high as they are convinced about the physical nature of the infestation, but adherence to psychotropic medications was low as they did not accept the presence of a mental illness.

Challenges for clinicians

Patients continue to demand evidence of infestation even though repeated investigations are negative. This must be dealt with appropriately and tactfully, with empathy and a consistent approach by clinicians in primary and secondary care. Anger and resentment towards professionals are common (Hinkle Reference Hinkle2011) and some accuse their doctors of incompetence when they fail to identify the parasites or pathogens that the patient believes are present. Most patients move between practitioners/specialists (doctor shopping) (Moriarty Reference Moriarty, Alam and Kalus2019) and are eventually lost to follow-up as they become increasingly frustrated and subsequently lose faith in the healthcare system.

People with delusional infestation are resistant and difficult to treat, leading to frustration for both patient and clinician (Winsten Reference Winsten1997). Clinicians might feel helpless and it is important to acknowledge the transference and feed back to the patient.

Cognitive–behavioural therapy can be used to challenge delusions to shift the belief, focusing on re-evaluating fearful thoughts of the infestation and work on fostering feelings of hope, control and self-worth (Freeman Reference Freeman2013). The clinician may work on limiting the time spent worrying about the infestation, improving sleep and increasing engagement in positive activities (Freeman Reference Freeman2013). It is important to be careful while addressing the unrealistic nature of the delusions, as attempting to persuade an individual that the delusion is incorrect can be self-defeating (Beck Reference Beck2007). Acceptance and mindfulness-based interventions may help to manage comorbid anxiety and depression and reduce associated distress of delusional beliefs (Louise Reference Louise, Fitzpatrick and Strauss2017; Shah Reference Shah, Taylor and Bewley2017). A paper by Lepping et al (Reference Lepping, Huber and Freudenmann2015) and its accompanying podcast give practical advice to clinicians regarding treatment for delusional infestation.

Dealing with patients who do not engage

A high percentage of people with delusional infestation continue to refuse help and will not engage in any therapeutic work. In these cases, a ‘do no further harm’ principal should be followed. Palliative interventions to alleviate symptoms, such as sedating or non-sedating antihistamines for sleep disturbances or pruritus, topical steroids and emollients, can be offered even though they do not alter the course of the disease (Moriarty Reference Moriarty, Alam and Kalus2019). Use of unnecessary medications such as antimicrobial agents and anthelmintic treatment is discouraged and unnecessary repeated testing should be avoided as this does not usually add clinical value (Hylwa Reference Hylwa, Bury and Davis2011).