Harvard Mental Health Letter

Delusions of infestation

Delusional parasitosis may occur on its own or as a complication of another disorder. It's enough to make your skin crawl, just thinking about it: insects, worms, fungi, or other pathogens colonizing a person's body. When there is no proof of actual infestation, however, the problem may be delusional parasitosis. This poorly understood disorder has gone by different names over the years, including Ekbom's syndrome (named for the first doctor to identify the phenomenon as a disorder), organic hallucinosis, unexplained dermopathy, and delusional infestation. The most recent manifestation of delusional parasitosis may be Morgellons, in which people believe they have been infested with fibers, threads, and other inanimate material. None of these names appears in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV). Instead, delusional parasitosis most closely resembles what the DSM-IV categorizes as delusional disorder, somatic type. Defined most simply, hallucinations are false perceptions, and delusions are false beliefs. Delusional parasitosis is a bit of a hybrid. The phenomenon involves both perception and belief. And the disorder's symptoms may be based on a misinterpretation of real sensations. This disorder may thus be related to paresthesia (Greek for abnormal sensation), akin to the feeling of "pins and needles."
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