Delusional infestation

Abstract

This papers aims at familiarizing psychiatric and nonpsychiatric readers with delusional infestation (DI), also known as delusional parasitosis. It is characterized by the fixed belief of being infested with pathogens against all medical evidence. DI is no single disorder but can occur as a delusional disorder of the somatic type (primary DI) or secondary to numerous other conditions. A set of minimal diagnostic criteria and a classification are provided. Patients with DI pose a truly interdisciplinary problem to the medical system. They avoid psychiatrists and consult dermatologists, microbiologists, or general practitioners but often lose faith in professional medicine. Epidemiology and history suggest that the imaginary pathogens change constantly, while the delusional theme "infestation" is stable and ubiquitous. Patients with self-diagnosed "Morgellons disease" can be seen as a variation of this delusional theme. For clinicians, clinical pathways for efficient diagnostics and etiology-specific treatment are provided. Specialized outpatient clinics in dermatology with a liaison psychiatrist are theoretically best placed to provide care. The most intricate problem is to engage patients in psychiatric therapy. In primary DI, antipsychotics are the treatment of choice, according to limited but sufficient evidence. Pimozide is no longer the treatment of choice for reasons of drug safety. Future research should focus on pathophysiology and the neural basis of DI, as well as on conclusive clinical trials, which are widely lacking. Innovative approaches will be needed, since otherwise patients are unlikely to adhere to any study protocol.

FIG. 1.

Specimen sign. Patients provide all kinds of proof of infestation, in this case a matchbox filled with skin particles and crusts on a piece of white cotton.

FIG. 2.

Skin lesions. Self-inflicted scratch excoriations in a patient with primary DI before (left) and after (upper right) antipsychotic treatment. Note that the skin lesions are limited to parts of the back that a right-handed elderly female can reach. At higher magnification, typical skin alterations in different stages of healing and scars of different ages can be seen (lower right).

FIG. 3.

Diagnostic overview (step 1).

FIG. 4.

Therapy overview (step 2).

FIG. 5.

Pathogenetic model (hypothesis). This illustration integrates the limited evidence available on pathophysiology and neural correlates of DI in a hypothetical network model.