Patient Characteristics and Treatment Approaches in Delusional Infestation Across Two Medical Centers: A Retrospective Study

Background: Delusional Infestation (DI) is a psychiatric disorder marked by a persistent, false belief of infestation despite medical evidence to the contrary. Large-scale research on DI is limited, with only one population-based study to date. DI remains poorly understood and difficult to manage. Methods: We conducted a multicenter retrospective chart review of adult outpatients seen in tertiary dermatology clinics at the University of Michigan and University of California, San Francisco between January 2021 and May 2024. Patients were identified using relevant ICD codes, and eligibility was confirmed by manual review for DSM-5 criteria for DI. Key clinical and demographic data were extracted, and relative risk was calculated using national prevalence data from NAMI and SAMHSA. Results: We identified 155 patients with DI; most were female (79%), non-Hispanic (94%), and white (73%). Mean age at onset was 54 years, with a three-year diagnostic delay. Delusions commonly involved parasites (25%) or bugs/insects (27%). Diagnostic evaluations included skin biopsy (34%) and skin scrapings (15%), with significant variation between centers. Substance use and psychiatric comorbidities were prevalent, with elevated relative risks compared to general population prevalence estimates. Treatments most often involved antiparasitic agents, pimozide, and second-generation antipsychotics; pimozide was associated with the highest rate of improvement. Conclusions: DI primarily affects middle-aged females and is marked by delayed diagnosis, frequent substance use, and psychiatric comorbidities. Despite varied diagnostic approaches, treatment outcomes remain poor. Multidisciplinary care and standardized protocols are needed to improve management and outcomes.