Psychiatric dermatology: Delusions of parasitosis

Key Points

Valhalla, N.Y. - Identifying precipitating events and treating patients with the antidepressant Lexapro (escitalopram, Forest Laboratories) can help patients overcome delusions of parasitosis, one expert says.

Delusions of parasitosis represent a monosymptomatic disorder characterized by the fixed, false belief that insects or other bugs are crawling over the body under the skin, says Michael J. Fellner, M.D., attending dermatologist at Metropolitan Hospital, New York Medical College.

Although the disorder can be associated with other psychiatric disorders such as schizophrenia and obsessive-compulsive disorder, he says that in most instances, the delusions remain encapsulated, and other mental functions remain intact.

The onset of delusions of parasitosis coincides with "a triggering life event such as loss of a loved one, loss of an apartment or loss of a job or other income," he says. "It's helpful to discuss the event with patients," who are usually middle-aged women, he adds. Furthermore, Dr. Fellner says he has found in clinical practice that prescribing escitalopram, 10 mg to 20 mg nightly, is helpful in managing the disorder. He says that this practice was suggested by New Jersey-based psychiatrist George Lieb, M.D., who theorized that delusions of parasitosis might be associated with an underlying depression. A selective serotonin reuptake inhibitor, escitalopram carries fewer side effects than the currently favored treatment, pimozide, which has been associated with potentially irreversible tardive dyskinesia and sudden death, Dr. Fellner says.

Delusions of parasitosis frequently prove frustrating for dermatologists to treat because patients often lack insight to connect emotional struggles to their apparent physical symptoms, and often refuse psychiatric consultations, he says. To better understand the role of precipitating events and the efficacy of escitalopram, he and a colleague observed and reported on a series of eight patients with the disorder (Fellner MJ, Majeed MH. Clin Dermatol. 2009 Jan-Feb;27(1):135-138).

Commonly, such patients bring in what they believe to be samples of the bugs in their skin, stored in jars, bottles or matchbooks - a phenomenon known as the "matchbook sign," Dr. Fellner says. Such samples usually include lint and cutaneous debris, but no bugs, he adds.

Defining cases

In one case, a 48-year-old Haitian female who had resided in the United States for 10 years complained of bugs crawling on her skin and coming out of her body, which had resulted in severe pruritus, widespread excoriations, ulceration and hyper- and hypopigmented scars, Dr. Fellner reports. These lesions were distributed evenly over her arms, legs and torso, he says.

Interviews with the patient revealed that she had recently broken up with her boyfriend and been evicted from her apartment shortly before the onset of her complaints. Dr. Fellner prescribed Eurax (crotamiton, Ranbaxy) lotion at bedtime, Temovate (clobetasol, GlaxoSmithKline) lotion for morning use and 10 mg of escitalopram nightly. Two weeks later, the patient showed improvement in her excoriations and fewer complaints about bug bites, he says.

In another case, a 59-year-old Hispanic female complained of severe generalized pruritus of three years' duration that she believed was caused by insects crawling on her body, Dr. Fellner says. Examination revealed xerosis of the arms and legs, as well as a maculopapular rash on the abdomen and arms. All these sites showed multiple excoriations, he says.

Upon interviewing the patient, Dr. Fellner says he learned she had lost several relatives - including three brothers - to disease during a relatively short period. For this patient, he prescribed crotamiton lotion and 10 mg escitalopram nightly, plus Lac-Hydrin (ammonium lactate, Ranbaxy) lotion in the morning and Diprolene (betamethasone dipropionate, Schering-Plough) ointment for affected areas after bathing.

Thanks to this regimen, "She did very well and was able to return to work. This was the most successful outcome in this series," which also included a 51-year-old female who, after three deaths in her extended family, was convinced that bugs from her recently purchased apartment were biting her arms and face, he says.

Success rate

Other patients were lost to follow-up, Dr. Fellner says. However, he says that since the study's completion, he and Dr. Majeed have prescribed escitalopram to approximately 20 patients, with success in 25 percent to 35 percent of cases.

"The success rate with this disease has not been very high, because many of the patients do not return for follow-up," Dr. Fellner says. Although it's not clear why this occurs, he says it could be because they're disillusioned with medical treatments, or their life circumstances don't permit regular visits.

Although the average dermatologist sees perhaps one patient with delusions of parasitosis in every 100 to 200 patients, Dr. Fellner says that he and his colleagues see two to five per 100, perhaps because their interest in the disease yields a growing number of referrals.

Delusions of parasitosis resemble Morgellons disease, he notes. "Some people feel Morgellons is a variant of delusions of parasitosis; some feel it's a separate entity." Patients with Morgellons disease believe there are "strings streaming out of the skin, which are usually pieces of lint. They also can have headaches and systemic symptoms that feel like the flu, which usually do not accompany delusions of parasitosis."

Dr. Fellner says one colleague, Haines P. Ely, M.D., of Grass Valley, Calif., has told him that in his patients with Morgellons, the precipitating incident generally takes the form of sexual abandonment.

"When his patients were counseled regarding this issue, they improved," Dr. Fellner says.

Disclosure: Dr. Fellner reports no relevant financial interests.