Delusional parasitosis: time to call it delusional infestation

Delusional parasitosis (DP) is a term that was coined by Wilson and Miller in 19461 to describe a particular psychocutaneous clinical picture which had previously been called by various names. The well‐recognized clinical picture of DP is reportedly an uncommon condition. Patients with DP hold a fixed belief that they are infected with organisms such as unicellular parasites, bacteria, viruses and worms; or infested with insects; or infiltrated by organic and nonorganic fibres, threads, ‘stealth viruses’ or other forms of inanimate particles known or unknown by medical science.2 We would like to support the change in the name proposed by Freudenmann and Lepping2 from ‘delusional parasitosis’ to the all‐encompassing term ‘delusional infestation’ (DI). This term better reflects the growing number of patients who do not believe they are infested by ‘parasites’, covers any species blamed by patients for their symptoms, and includes the so‐called ‘Morgellons syndrome’. The condition has been known by a variety of names since its initial description as ‘acarophobie’ in 1894 by Thieberge:3 these include ‘Dermatozoenwahn’ (Ekbom’s syndrome), delusion of infestation and parasitophobia.4‘Delusional parasitosis’ (the term preferred by many up until now) has been a more accurate term than parasitophobia as it is a true delusion, i.e. a fixed false belief, rather than a phobia (a persistent irrational fear). The diagnosis of DI can be subdivided into primary and secondary disorders. Primary functional delusional disorder is classified in DSM‐IV‐TR5 as delusional disorder somatic type and in ICD‐106 as persistent delusional disorder. Nevertheless, the predominant delusional theme for most is that of an infestation. Some patients also see this as an infection or infiltration of one’s own body or immediate environment. We therefore prefer the term DI as it includes patients with a delusional belief that they are infected with any kind of vivid and inanimate pathogen. The basic phenomenology of the disease has remained unchanged for centuries, but as with most psychiatric disorders, the exact nature of the patients’ presentation is context dependent and changes over time. The term DI captures all the various presentations and, what is more, it is open to all future kinds of pathogens and infesting species which will (no doubt) emerge.2 Although reportedly uncommon, the average dermatologist will see two to three patients with DI every 5 years.7 The annual incidence of DI has been estimated at 20 cases per million.2 The female to male ratio under the age of 50 years is equal but over the age of 50 years the incidence is reported as 2 : 1.2 There is a bimodal distribution with a peak between 20–30 years and another at > 50 years,2 and there are frequent reports of the delusions being shared with a relative or close friend (folie à deux; 8–12% of cases of DI),8 and occasionally more than one person.9 It is likely that the incidence and prevalence of DI have been systematically under‐reported. Clinicians who set up clinics for patients with DI and related disorders are soon inundated with patients who have hitherto been ‘held’ in primary care, or have ‘doctor‐shopped’ so much that there is no one clinician who holds clinical responsibility for the patient.2 In many cases the aetiology is unknown. It may follow a real infestation, be associated with recreational drug use (especially alcohol, amphetamines, cannabis and cocaine), be a dementia‐related psychosis in the elderly, and be associated with other organic disease. The management of patients with DI can be challenging. Treatment of secondary DI should begin with treating (where possible) underlying causes, in addition to treating the delusion itself. For example, it is important to treat any recreational drug and alcohol abuse as well as treating the patient’s skin and the delusion. Treatment of the skin as well as the psychiatric disease is crucial, not least because that is usually the patient’s main focus. Randomized controlled trials in the treatment of the delusion itself are lacking in part due to the nature of the condition and the obvious difficulty of recruiting patients for trials with informed consent. When referred to a purely psychiatric clinic, patients with DI will often default their appointments.2 Conversely, it is also difficult to manage these patients in a standard dermatology clinic as they often take considerable time and other resources to engage in therapeutic management. Lepping and coworkers2, 10 conducted a systematic review of the effectiveness of antipsychotics in primary DI, and concluded that there was weak evidence that they are effective as there are no randomized controlled clinical trials. They describe the difficulties encountered by those trying to study pharmacological management of this group of patients. Healy et al.11 have reported a recent U.K. audit of the use of atypical antipsychotics in the treatment of DI. These authors report successful treatment of DI with atypical antipsychotics (often risperidone in surprisingly low doses, for example 0·5–1 mg daily) in up to 75% of patients with DI. Patients who respond to second generation antipsychotics will usually start to describe benefit in their symptoms after 4–6 weeks of treatment, but the treatment will usually need to be continued for 6 months to 1 year. In the absence of evidence‐based data there is some rationale in using atypical antipsycotics as first generation antipsychotics (for example, pimozide) may be associated with cardiotoxic side‐effects, albeit that these side‐effects are reported in patients who require larger doses of pimozide than those needed to treat DI. We have recently followed up this audit with a protocol to perform a randomized controlled clinical trial of risperidone vs. no treatment for patients with DI. However, we have been unable to recruit patients to the trial (because engagement with patients with DI is difficult enough without seeking consent and psychometric testing). We believe that the renaming of ‘delusional parasitosis’ as ‘delusional infestation’ is an advance in the terminology of this difficult condition. DI describes more accurately the clinical picture currently encountered by clinicians, and most especially the widening spectrum of ‘pathogens’ to which patients ascribe their symptoms.