Delusional Parasitosis

Abstract

Delusional parasitosis is a rare psychiatric disorder. Patients with delusional parasitosis have a false and fixed belief that they are infested by parasites. According to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, the disorder is characterized by a nonbizarre delusion of the somatic type that persists for at least 1 month. Patients must not meet criterion A for schizophrenia, and the delusion cannot be due to the effects of a substance or a general medical condition.1American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders: DSM-IV-TR, 4th ed. Text revision. American Psychiatric Association, Washington, DC2000Google Scholar The mean age of onset is 56.9 years, and the male-to-female ratio is 1:1.5.2Zomer SF De Wit RF Van Bronswijk JE Nabarro G Van Vloten WA Delusions of parasitosis: a psychiatric disorder to be treated by dermatologists? an analysis of 33 patients.Br J Dermatol. 1998; 138: 1030-1032Crossref PubMed Scopus (77) Google Scholar Patients describe an invasion of a parasite on or inside the skin; they may bring in objects such as hair, lint, or skin, “the matchbox sign,” as “proof” of the infestation despite normal findings on examination.3Le L Gonski PN Delusional parasitosis mimicking cutaneous infestation in elderly patients.Med J Aust. 2003; 179: 209-210PubMed Google Scholar In an effort to remove the insects, patients may excoriate the skin or apply skin-toxic agents. When the same delusion develops in another individual, often a spouse, the disorder is termed folie a' deux.1American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders: DSM-IV-TR, 4th ed. Text revision. American Psychiatric Association, Washington, DC2000Google Scholar Patients rarely seek the help of a psychiatrist; rather, because of their belief in a somatic complaint, patients often see primary care physicians or dermatologists for treatment.2Zomer SF De Wit RF Van Bronswijk JE Nabarro G Van Vloten WA Delusions of parasitosis: a psychiatric disorder to be treated by dermatologists? an analysis of 33 patients.Br J Dermatol. 1998; 138: 1030-1032Crossref PubMed Scopus (77) Google Scholar, 3Le L Gonski PN Delusional parasitosis mimicking cutaneous infestation in elderly patients.Med J Aust. 2003; 179: 209-210PubMed Google Scholar Management initially involves ruling out a general medical condition and excluding the use of drugs, illicit or prescribed. Traditionally, treatment is pimozide, a dopamine antagonist, although some patients may respond to atypical neuroleptics such as haloperidol or risperidone. Duration of treatment varies from 2 weeks to 3 months before use is tapered, but compliance can be challenging.2Zomer SF De Wit RF Van Bronswijk JE Nabarro G Van Vloten WA Delusions of parasitosis: a psychiatric disorder to be treated by dermatologists? an analysis of 33 patients.Br J Dermatol. 1998; 138: 1030-1032Crossref PubMed Scopus (77) Google Scholar, 4Safer DL Wenegrat B Roth WT Risperidone in the treatment of delusional parasitosis: a case report [letter].J Clin Psychopharmacol. 1997; 17: 131-132Crossref PubMed Scopus (37) Google Scholar, 5Hanumantha K Pradhan PV Suvarna B Delusional parasitosis—study of 3 cases.J Postgrad Med. 1994; 40: 222-224PubMed Google Scholar