to the editor: A 41-year-old nurse requested a second opinion about a bowel disorder. She related her symptoms to a previous trip to Mexico, where she acquired a self-limited diarrheal illness. She complained of recurrent diarrhea that she believed was caused by a parasite acquired while she was in Mexico.

Findings on initial physical examination were unremarkable, and stool studies were negative. Because of persistent symptoms, the patient requested a gastroenterology referral. Results of multiple tests (ova and parasites, cryptosporidium antigen, giardia antigen, colonoscopy, esophagogastroduodenoscopy, mucosal biopsies and serum chemistries) were all within normal limits.

I reassured the patient that there was no evidence of an occult parasitic infection. At the time of this presentation, the patient was well groomed and appeared in no distress. She calmly explained her dilemma. She suffered no adverse consequences in other areas of her life and was not depressed. She only wanted to find and eliminate the parasite that was tormenting her. Findings on repeat physical examination were normal, and psychotherapeutic referral was suggested. The patient became hostile, promptly left the office and was lost to follow-up.

Originally described in 1894,¹ delusions of parasitosis (DOP) has been variously referred to as dermatophobia, parasitophobic neuro-dermatitis, parasitophobia or entomophobia.² Central to the diagnosis is a fixed, false belief of a parasitic infestation. Patients are usually fully functional in all other areas.

The prevalence of DOP is not known. The condition is more common in middle-age women. No risk factors have been identified, and no predilections among socioeconomic, occupational or racial backgrounds is evident. In 12 percent of patients, the delusion of parasitic infestation is shared by a significant other—a condition known as “folie a deux.”³

Patients often seek the advice of multiple physicians to seek sympathy. They often present with a container holding the purported parasite (the “matchbox sign”⁴). Patients often have received multiple treatments from multiple physicians and will also use self-concocted preparations to rid themselves of the perceived infestation.

Following a thorough history and physical examination, appropriate initial laboratory studies include a complete blood count, serum electrolytes, thyroid function tests, rapid plasma reagin, urinalysis and a drug screen. An electroencephalogram, B₁₂/folate levels or computed tomography may be appropriate based on specific patient presentation.

Successful treatment of delusional parasitosis is difficult and requires formulating a sense of trust with the patient. A multidisciplinary approach is preferred. The following steps are useful in approaching patients with DOP⁵:

1. Ensure that the diagnosis is correct.

2. Listen empathetically.

3. Ask how the condition has affected the patient's quality of life.

4. Establish the trust of the patient.

5. Be alert to any area where the patient will allow you to help.

6. Reduce the patient's sense of isolation.

7. Consider use of medication to ease the patient's anxiety or psychosis.

Pimozide (Orap), a neuroleptic agent, has traditionally been the drug of choice for the treatment of DOP.⁶ The initial dosage is 1 mg per day. This can be increased weekly by 1-mg increments until a clinical response is achieved. Most patients respond at a dosage of 4 to 10 mg per day.³ The maximum dosage is 20 mg per day.