Also communicate with other specialists to gauge medication history, confirm test findings, and rule out medical causes.
Pharmacotherapy. If symptoms do not resolve after 1 or 2 days of observation, look for a comorbid medical or mental disorder. Prescribe an atypical antipsychotic such as risperidone, 2 to 4 mg/d, or olanzapine, 2.5 mg/d, both of which have been effective against delusional parasitosis.14,16 Keep dosages low to reduce risk of sedation, extrapyramidal symptoms (EPS), and tardive dyskinesia.
Suggesting a psychotropic to patients who are convinced their problem is not psychiatric can be difficult. Try saying:
- Some people are more sensitive than others to sensations on their skin or in their body. This medication will help you tolerate the sensations.”
- or, “This drug will help reduce the anxiety your problem is causing.”
Pimozide has shown efficacy against delusional parasitosis in placebo-controlled trials,17,18 but it can alter cardiac conduction, especially at higherthan-recommended dosages. Start pimozide at 1 mg/d and increase by 1 mg/week until clinical response is achieved. Most patients respond to dosages used to treat psychotic disorders (4 to 10 mg/d).19 Order a baseline and periodic ECG to monitor for QTc prolongation, and do an abnormal involuntary movement scale examination every 3 to 6 months to test for EPS.
Other treatments that have shown benefit in case reports include naloxone, 10 mg/d;20 haloperidol, 10 mg/d; trifluoperazine, 15 mg/d; chlorpromazine, 150 to 300 mg/d; and electroconvulsive therapy.7
We have found that prognosis usually is poor after first- and second-line treatments have failed. Continue to search for a missed disorder, and add an antidepressant if an underlying depression is found or suspected.
Psychotherapy. Perform supportive and harm reduction psychotherapy immediately after diagnosis. Supportive, rapport-building approaches can get the patient to comfortably discuss the issues that led to the delusion and help him/her confront a relapse. Harm reduction can discourage patients from requesting unnecessary invasive tests, using medications and toxic insecticides, or other potentially harmful behaviors.
Cognitive-behavioral therapy may help some patients with refractory delusional parasitosis, if they have enough insight to continue treatment.
Follow-up: A bug-free future
Mrs. K was released from the hospital after 4 days, and her delusional symptoms were gone after another 3 days. We followed her for 6 months.
Upon discharge, Mrs. K and her cat moved in with her daughter’s family. Within a few weeks she was able to visit her workplace and explain what had happened. She stopped taking risperidone after 2 weeks because of excessive sedation. No depressive symptoms were present after 3 months; escitalopram was stopped.
Mrs. K’s husband continued to drink and confine himself to the house. Upon visiting him, she was horrified to find the furniture still covered with plastic and the windows taped shut. Mrs. K threatened to divorce him if he did not seek help. He eventually was treated and has been sober—and bug-free—for 15 months.
Related resources
- Bohart Museum of Entomology, University of California, Davis: Delusional parasitosis. http://delusion.ucdavis.edu.
- Chlorpromazine • Thorazine
- Escitalopram • Lexapro
- Haloperidol • Haldol
- naloxone • Narcan
- Olanzapine • Zyprexa
- Pimozide • Orap
- Phenelzine • Nardil
- Risperidone • Risperdal
- Trifluoperazine • Stelazine
Dr. Matthews is an American Psychiatric Association Bristol-Myers Squibb Co. fellow in public and community psychiatry.
Dr. Hauser receives research/grant support from and is a speaker for AstraZeneca Pharmaceuticals, Eli Lilly and Co., GlaxoSmithKline, and Hoffman LaRoche. He is also receives research/grant support from Schering-Plough Corp. and is a speaker for Abbott Laboratories and Janssen Pharmaceutica.