Patients with delusional infestation (delusional parasitosis) often require prolonged treatment as recurrence of symptoms after cessation of treatment is common: an observational study.

Abstract

Delusional infestation (DI) is an uncommon psychiatric disorder in which patients present with the false and fixed belief of infestation. Numerous studies have demonstrated improvement with pharmacological treatment; however, recurrence rates on cessation of treatment remain unknown. To assess the clinical response and recurrence rates following treatment for DI. All patients with DI seen in our combined dermatology/psychiatry clinic to date (n=73) were offered pharmacological therapy. Patients were contacted to complete a telephone questionnaire to assess clinical outcomes, including remission and recurrence rates following treatment. Fifty-nine of 73 (81%) patients with DI received treatment, of whom 40/59 (68%) reported improvement or resolution of symptoms, and the remaining 19/59 (32%) failed to respond. Fifteen of 40 patients with DI completed a course of treatment, 12/40 patients are still undergoing treatment, and outcomes are unknown for 13/40. Of those who completed treatment, 11/15 (73%) reported total remission for at least 9months after discontinuing treatment (range 9months-2·5years). Recurrence of symptoms occurred in 4/15 (27%) within 4months of stopping treatment. Pharmacological treatment of DI can be effective, particularly in a combined dermatology/psychiatry clinic. Most treated patients have a good prognosis, and a remission period can be expected. However, more than 25% of patients may relapse on stopping treatment, with the greatest risk being within the first few months of discontinuation. These patients may require longer treatment courses, or long-term maintenance therapy for symptom control, although further studies are needed to provide recommended guidelines on drug and dosing regimen.