Delusions of parasitosis.

The most common monosymptomatic hypochondriacal psychosis encountered by a dermatologist is delusions of parasitosis. In this condition, patients have an "encapsulated" fixed, false belief that they are infested with parasites or have foreign objects extruding from their skin. The patient will often experience feelings of biting, crawling and stinging related to the delusion. Most patients do not have other major psychiatric problems outside of their encapsulated delusion. The patient usually presents with a long history of symptoms and multiple visits to physicians in more than one specialty. Without an informed approach to these patients that focuses on the development of therapeutic alliance, clinical interactions can become very unpleasant. However, when treated with pimozide, risperidone, or other antipsychotic medications, patients have a very high response rate. Therefore, it is important for dermatologists to be able to handle these cases and know that the development of the therapeutic alliance is the key step to successful management.