Delusional infestation: An update

NTRODUCTION AND NOMENCLATURE

Delusional infestation (DI) is a monosymptomatic hypochondriacal psychosis characterized by a fixed, false belief that one is infested with a parasite, bacteria, worm, insect, virus, fungus, or inanimate material, despite lack of objective evidence.^[1-3] It is categorized as a somatic delusional disorder under the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5TR) classification and as delusional disorder (code 6A24) under International Classification of Diseases 11^th Revision (ICD-11) (2019).^[4,5] This disease was first described by Georges Thibierge, a French dermatologist, in patients who actually had scabies and were treated successfully, and also in those who never had scabies but felt that they were infested. He called these patients “les acarophobes,” implying an irrational fear of mites. DI has earlier been referred to by several terms, e.g., delusions of parasitosis, delusional parasitosis, Ekbom syndrome, acarophobia, parasitophobia, and pseudoparasitic dysesthesia. At present, DI is the preferred term, reflecting that DI is not a phobic disorder, and patients may present with a range of infesting organisms, fungi, animate material, etc., not just parasites.^[6-8]

As a delusional disorder, the patient has an unshakable belief, even though no infesting organism or material can be demonstrated. In a few cases, DI can be due to an overvalued idea and may be more likely responsive to critical reasoning. However, most of the patients with DI have a primary delusion (monosymptomatic hypochondriac psychosis). DI can occur as a shared delusion among spouses, family members, carers, and friends (folie à deux, folie à trois, etc.).^[9] In DI by proxy, patients complain that their child, pet, or friend is infested despite evidence to the contrary.^[10]

Morgellons disease (or syndrome) is a delusion marked by a persistent belief that solid fibers, threads, or substances are being extruded from the skin.^[11] Similar to DI, these patients have sensations of crawling or stinging. Some workers suggest a possible dermatological or infectious basis (e.g., Lyme disease). Both these conditions have typical somatic preoccupations and skin-damaging behaviors (e.g., scratching and picking) and resist psychiatric referral. Morgellons disease has been considered a variant of DI, although many workers have distinguished it from DI. Morgellons disease may consist of various phenomena.^[2,7,12,13]

HISTORICAL BACKGROUND

In 1889, Magnan and Saury described tactile symptoms in several patients with regular use of cocaine, now called the “cocaine bugs” (signe de Magnan).^[2] However, the first formal description of DI was given by Georges Thibierge, a French dermatologist, in 1894, in patients having an irrational fear of mites (“les acarophobes”). Later, in 1938, Swedish psychiatrist Karl-Axel Ekbom described the disease as “der präsenile dermatozoenwahn” and conceptualized a presenile involutional or organic brain syndrome. His disease model was based on the study of seven postmenopausal female patients and earlier published cases.^[14] In 1946, Wilson and Miller comprehensively reviewed all available cases (and described their own six cases) and introduced the term delusional parasitosis. They hypothesized four different etiologies: toxins, schizophrenia, old-age depression, and paranoia/delusional disorder.^[15] In 1960, German Entomologist Döhring published a large series of 77 cases of DI as “illusory vermin infection syndrome.”^[16] The term DI was first proposed by Bewley et al.^[6] A comprehensive historical account of this illness was recently described by Orsolini et al., in 2020.^[17]

EPIDEMIOLOGY

DI is a relatively rare but disabling condition, with a worldwide incidence of the disease estimated to be about 1.9–27.3 cases per year per 100,000 people.^[18,19] A prevalence rate quoted as 17 per million people per year is an underestimate, probably due to underreporting, particularly in the elderly.^[20,21] DI can rarely be seen in children, but the peak incidence is in adults in their fifties. There does not seem to be any gender predilection, but as affected males may present to clinicians much less, research indicates a male-to-female ratio of 1:2.5. All ethnicities are susceptible to the disease.^[22]

ETIOPATHOGENESIS

Patients may sometimes describe an inciting event.^[23] This event may be an actual insect or insect bite, a hallucination (i.e., sensory experience in the absence of a stimulus), or an illusion. Later, this may convince the patient to believe that there was an actual infestation, thus initiating the disease process. Functional magnetic resonance imaging study of the brain of these patients demonstrated altered central processing of infestation-relevant stimuli in DI patients with abnormal skin sensations. The authors hypothesized a heightened threat processing within the amygdala, increased salience of skin representations within the insula, and compromised prefrontal capacity for self-regulation and appraisal.^[24] Isolated reports have proposed the possible etiologic roles of supplementary motor area dysfunction and reduced dopamine transporter (DAT) function leading to increased synaptic dopamine in striatal regions.^[25,26]

In secondary DI, several organic and psychiatric diseases, infections, malignancies, and micronutrient deficiencies etc., may be associated [Table 1].^[27,28] Approximately half of DI patients may have concomitant diseases, although causality may not be proven in all cases. However, occasional patients may have other delusions as well, for example, DI associated with a co-morbid psychiatric disease (e.g., schizophrenia). Substance abuse, including methamphetamine use, alcohol withdrawal, and acute cocaine use (described as “cocaine bugs”)^[29] and certain medications (e.g., topiramate, ciprofloxacin, amantadine, steroids, ketoconazole, and phenelzine) may present with clinical features of DI. In clinical practice, it is essential to rule out these conditions and treat nutrient deficiencies for optimal treatment outcomes.

CLINICAL FEATURES

DIAGNOSIS

The diagnosis of DI is made by first excluding other psychiatric conditions. The DSM-5-TR defines DI as a psychotic disorder characterized by one or more delusions lasting for at least 1 month.^[4] In the ICD-11, DI is classified under delusional disorders, as a subtype of persistent delusional disorder.^[5] The patient should have a fixed, false belief in infestation without objective physical evidence. If the delusion is part of another psychiatric disorder, such as schizophrenia, a separate diagnosis of delusions of parasitosis cannot be made. Second, other illnesses, medication use, drug abuse, etc., should be ruled out [Table 1].^[38] Patients may insist on close and microscopic examination of skin fragments and other materials they bring. Some patients ask for skin biopsies. Some authors suggest that a biopsy may be performed to rule out a primary cutaneous disease and help build a therapeutic rapport with the patient.^[39] However, a biopsy is an invasive procedure and is better avoided. Dermatoscopy, with a hand-held dermatoscope, in DI can be performed to examine the patient or materials they bring (the “dermatoscopic” matchbox sign), and it is a quick, non-invasive, and convenient examination method.^[40] Skin biopsies are inconclusive and usually show non-specific dermatitis/dermal inflammation.^[30,41]

MANAGEMENT

Early diagnosis and appropriate intervention are critical for DI, as patients with a short duration of delusion tend to have a better prognosis with treatment.^[42] Untreated patients are likely to become isolated, and their condition may become more resistant to therapy.^[22] Treatment is challenging, and the patient would likely have consulted many physicians (doctor-hopping) and be frustrated. They may be hostile toward the new healthcare provider and may straightaway refuse a psychiatric evaluation.^[43] The crucial step in effectively treating a DI patient is establishing a strong therapeutic rapport. Gaining trust of the patient through empathy and support is essential in the physician–patient therapeutic relationship [Figure 1].^[3]

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Figure 1:

Stepwise intervention plan for delusional infestation patients.

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Some workers have suggested an initial approach, which is to take a thorough history and to avoid confrontation during the first clinical encounter. A complete diagnostic workup of the patient has been recommended to exclude associated diseases and malignancies [Table 2].^[3,44] Afterward, the patient may be started on a low dose of antipsychotic medication after explaining that “it has helped other patients with similar complaints.”^[7,23,30] As the pharmacologic action of the medication takes effect, the DI patient is likely to improve clinically. As the therapeutic alliance is established, the medication dosage may be titrated and optimized.

Antipsychotic medications are the mainstay of treatment.^[45] Classically, pimozide, a first-generation antipsychotic, has been studied for treating DI and was found to be very effective, even in many chronic patients.^[46,47] Historically, pimozide was first used by Riding and Munro in 1975.^[48] In their second case series, a complete response was seen in 3 out of 6 patients with no response in a single case (of suspected personality disorder).^[49] Later, pimozide was considered effective by many workers.^[50-52] Pimozide works by blocking dopamine receptors at low doses to reduce psychotic symptoms and has opioid-antagonistic effects that may help with skin sensations. However, pimozide is known to cause QTc prolongation (torsades de pointes – a specific form of polymorphic ventricular tachycardia) and may cause significant hemodynamic compromise and often mortality. Baseline electrocardiogram and frequent cardiac evaluation are recommended, especially in older patients or those with heart disease. At present, pimozide is not a preferred therapy for DI.^[3]

First-line medications for DI consist of second-generation antipsychotics (SGAs, also called atypical antipsychotics). In 1995, risperidone (an SGA) was successfully used in DI by Gallucci and Beard.^[53] At present, most commonly recommended SGAs include quetiapine, olanzapine, risperidone, and aripiprazole.^[23,54-60] Aripiprazole is sometimes referred to as a third-generation antipsychotic owing to its unique mechanism of action as a partial dopamine agonist, leading to more balanced dopamine levels in the brain.^[61] These medications should be employed at the lowest possible dosage to prevent side effects, including extrapyramidal and metabolic side effects (weight gain, hyperglycemia, precipitation of diabetes). The dosages and main side effects are described in Table 3.^[3,44,62] Newer antipsychotics, such as lurasidone, paliperidone, and brexpiprazole, can also be considered for therapy.^[63,64] However, a Cochrane Review in 2021 found no evidence from randomized controlled trials available to compare the treatment of primary DI with placebo and did not make any conclusions regarding the effects of treatments for primary DI.^[65] A more recent systematic review in psychodermatology identified only one trial on DI, highlighting the lack of evidence for its management, and underscoring the need for robust clinical data comparing various antipsychotics in the treatment of DI.^[66]

A step-wise intervention plan for managing DI patients is provided in Figure 1. Though pharmacologic interventions remain the cornerstone of management, structured psychotherapeutic approaches may aid in patient engagement and adherence [Figure 2].

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Figure 2:

Basics of care of delusional infestation patients.

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PROGNOSIS

Adherence to antipsychotic treatment is critical, and as the patient experiences symptom relief, compliance is likely to improve. In many patients, after remission, the antipsychotic medication can be tapered to a maintenance dose after a few months while maintaining efficacy. Most patients usually require long-term, low-dose maintenance therapy. Recent work indicates improved clinical outcomes in multidisciplinary clinics.^[67]

FUTURE DIRECTIONS

Biomarkers of the DAT function may be helpful in future research to elucidate the risk of DI and personalize therapy.^[68] Designing randomized trials to compare antipsychotics (risperidone, aripiprazole, and olanzapine) and psychotherapeutic adjuncts will generate further evidence for the treatment of DI and offer alternative options for patients intolerant to traditional antipsychotics.

CONCLUSION

Treatment of a DI patient is possibly the ultimate test of the most astute dermatologist. One must be skilled not only as a clinician but also as a communicator who can empathize and connect with these patients. Therefore, dermatologists must approach these patients constructively and become comfortable prescribing select antipsychotic agents. These are the essential steps for the care these patients need.