Efficacy of Antipsychotic Treatment for Delusional Infestation: A Retrospective Cohort Study.

Background: Delusional infestation (DI) is a rare psychiatric disorder characterized by false beliefs in infestation, often presenting to dermatology clinics with unexplained skin complaints. Antipsychotic treatments are commonly used; however, their comparative efficacy in DI remains unclear.

Objective: This study aimed to evaluate the comparative efficacy of six antipsychotics-pimozide, olanzapine, aripiprazole, risperidone, amisulpride, and paliperidone-in the treatment of DI.

Methods: A retrospective observational cohort study was conducted at a university hospital in Turkey, analyzing anonymized medical records from 36 patients diagnosed with DI and treated with one of six antipsychotics between 2014 and 2023. Equivalent doses of antipsychotics were standardized to 100 mg of chlorpromazine. Clinical Global Impression Severity (CGI-S) scores were used to assess treatment response at baseline, 3 months, and 6 months. Repeated measures ANOVA was employed to compare the efficacy of each antipsychotic over time.

Results: All six antipsychotics significantly reduced CGI-S scores over the 6-month period (P < 0.001). Amisulpride, followed by paliperdione and risperidone, demonstrated the most substantial improvements, with mean CGI-S scores decreasing from 5.43 to 1.71, 5.20 to 2.00, and 5.17 to 2.00, respectively, by 6 months. Pimozide showed reasonable efficacy. Aripiprazole and olanzapine had the least efficacy after 6 months. There was a significant reduction over time in aripiprazole showing the strongest initial response.

Conclusions: Amisulpride, followed by paliperidone and risperidone, emerged as the most effective treatments for DI, with the greatest reductions in symptom severity, confirming previous studies. The effect is significant over time.