Contributor: Taylor Lynch, MD

Educational Pearls:

Delusional parasitosis is a subtype of the psychiatric condition delusional disorder
- Defined as a fixed, false belief of infestation by parasites or other organisms
- A somatic type of delusional disorder
Primary delusional parasitosis
- Occurs in the absence of other psychiatric or medical conditions
Secondary delusional parasitosis
- Causes include methamphetamine use disorder, schizophrenia, neurologic diseases, or medical conditions such as thyroid disease
Pathophysiology
- Poorly understood
- Upregulation of striatal dopamine system is implicated
Management
- Form a strong therapeutic alliance and do not discredit the patient immediately
- Perform a full physical exam
  - This helps reassure the patient and strengthen the therapeutic alliance
  - Some day there may be a patient in whom this is not a delusion
Treatment & Management
- Discontinuation of substances if substance-induced
- Antipsychotic medications like risperidone or olanzapine

References

Lepping P, Russell I, Freudenmann RW. Antipsychotic treatment of primary delusional parasitosis: systematic review. Br J Psychiatry. 2007;191:198-205. doi:10.1192/bjp.bp.106.029660
Moriarty N, Alam M, Kalus A, O'Connor K. Current Understanding and Approach to Delusional Infestation. Am J Med. 2019;132(12):1401-1409. doi:10.1016/j.amjmed.2019.06.017
Skelton M, Khokhar WA, Thacker SP. Treatments for delusional disorder. Cochrane Database Syst Rev. 2015;2015(5):CD009785. Published 2015 May 22. doi:10.1002/14651858.CD009785.pub2

Summarized and Edited by Jorge Chalit, OMS4

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Episode 978: Delusional Parasitosis

Emergency Medical Minute