John Koo, MD, and Scott A. Norton, MD, MPH, join host Lorenzo Norris, MD, for this special edition of the Psychcast. This is a crossover episode with our sister podcast, Dermatology Weekly. Dr. Koo is a psychiatrist and a dermatologist at the University of California, San Francisco. He has no disclosures. Dr. Norton is a dermatologist with the Uniformed Services University of the Health Sciences in Bethesda, Md., and with George Washington University, Washington. He has no disclosures. They are featured in an article on this topic online at MDedge.com/Psychiatry. Dr. Norris is associate dean of student affairs and administration at George Washington University. He has no disclosures. Take-home points Delusional infestation or delusions of infestation, also known as delusional parasitosis, is a fixed false belief that one has an infestation of animate or inanimate pathogens, despite strong evidence against infestation. Common precipitants of delusional infestation include previous exposure to external or internal parasites, stress, and travel. The condition is more common among highly functional older women. A recent study estimated the prevalence of delusional infestation as 1.9/100,000, though the condition is an area of limited study. Delusional infestation is poorly recognized by physicians, therapists, and families, which leads patients to search for an external cause of the symptoms and contributes to distress for patients and their loved ones. Patients with delusional parasitosis often lack insight into their disease, and it can be difficult to persuade them to take the recommended treatment of antipsychotics. Low-dose pimozide, a first-generation antipsychotic, is the most common treatment for delusional infestation, particularly because it does not have Food and Drug Administration approval as a treatment for psychosis. Therefore, patients are less biased against taking this medication. Summary Delusions of infestation are a monosymptomatic hypochondriacal psychosis in which the only delusion present is one of infestation, and patients do not have other symptoms of psychotic spectrum illness. Secondary delusions of infestation may occur in individuals who use drugs, such as methamphetamine or cocaine, or who have a primary psychotic disorder, such as schizophrenia. Delusions of infestation is related to Morgellons disease, which is defined as a skin condition characterized by the presence of “threads” or filaments that patients believe are embedded in their skin and might be accompanied by stinging and itching sensations. Patients with delusions of infestation usually present to a primary care physician or ED with symptoms of abnormal sensations of their skin, including crawling sensations. In addition, patients usually bring personal proof of their condition, such as a small bag of “specimens,” including pieces of lint, threads, or scabs. Some patients also bring in journals detailing the timing and associated factors of their symptoms. Dr. Norton advises that physicians treating the patients with delusions of infestation should mentally prepare themselves against initial bias and set aside time for longer visits or several follow-up visits. Dr. Norton starts with the premise that the patient has an actual infestation or other underlying cause of their pruritus and performs a thorough, full-body exam for dermatologic conditions, and examines the materials patients bring with them using a double-headed microscope – so that he and the patient can look at the specimens together. Dr. Koo often tells patients that they have Morgellons disease because it does not include the stigmatizing term of “delusional.” He reframes Morgellons as an infestation that cannot be cured by internal or external antiparasitic medications. He then pivots away from etiology to validation of their emotions and eventually to treatment. Dr. Koo usually often starts treatment with pimozide because it is an antipsychotic with FDA approval for T