DEFINITION

• Delusional parasitosis (DP), or delusional infestation, is a psychiatric disorder characterized by a fixed false belief that one’s body is infested with pathogens or, rarely, inanimate objects. Though the specific organ and type of infestation may vary, presentations typically involve the skin and small organic pathogens such as worms, mites, files, or unspecified insects. ’Morgellons’ is an example of inanimate DP where patients believe they have skin lesions that are filled with a fibrous material.
• DP classified as a form of somatic delusion rather than a diagnostic entity in the DSM5.
• Case of DP can be divided into primary or secondary disorders depending whether a patient’s DP is a symptom of an underlying illness. Secondary causes include psychiatric conditions (e.g. affective disorders with psychotic features, schizophrenia, substance use), neuropsychiatric conditions (e.g. stroke, dementia), and medical conditions such as diabetes and vitamin deficiencies. Symptoms may be transient during instances of stimulant intoxication or alcohol withdrawal. Primary DP is a form of monosymptomatic delusional disorder that occurs in the absence of one of these conditions. [1][2]

History

• 1857 - English dermatologist William Wilson describes DP-like condition under umbrella of ’skin neurosis’.
• 1894 - First clear description from French dermatologist George Thibierge who coins ’acarophobia’ (fear of tiny bugs) to describe patients who believed they were infested with mites.
• 1938 - Ekbom describes condition as ’präsenile Dermatozoenwahn’ (presenile dermatologic delusion), recognizing incidence in older adults.
• 1946 - Wilson and Miller - introduce term ’delusion of parasitosis’ emphasizing a disorder of belief rather than anxiety and fear (entomophobia, parasitophobia, acarophobia).
• 1975 - Riding and Munro demonstrate response to Pimozide in 4 patients with ’monosymptomatic hypochondriacal psychosis’.
• 2007 - Lepping and Freudenmann conduct systematic review demonstrating comparable remission rates with typical and atypical antipsychotics for DP.

Synonyms/eponyms: Delusions of parasitosis, delusional infestation, Ekbom syndrome, [instance of] monosymptomatic hypochondriacal psychosis