Prescription Stimulants as a Risk Factor for Delusions of Infestation: Results of a Large Case-Control Study in a Psychodermatology Clinic

Abstract: Background/Significance: Patients with delusions of infestation (DI) believe that there are organisms or objects in their skin despite the absence of objective evidence. DI impairs function and decreases quality of life. Patients often scratch, pick, and dig in their skin causing substantial physical damage. Prior studies of patients with DI have been largely limited to retrospective case series [1] and risk factors for development of DI are poorly understood. Clinical experience and at least one small case control study raise concern for an association between prescription medication (stimulants and opioids) and DI [2].

Methods: We conducted a retrospective case-control study of patients with DI. Cases were identified via chart review and matched 1:1 on age (±5 years), sex, race, and ethnicity with patients without DI who were seen in the same location for general dermatological complaints. Chi-square analysis was used to evaluate the difference in rate of prescription stimulant and prescription opioid (full- or partial-agonist) use between cases and controls. We also examined treatment response in cases prescribed stimulants compared to cases who were not.

Results: The case cohort consisted of 96 patients seen between February 2020 and February 2023. The majority of patients were single (n=62; 64.6%), non-Hispanic (n=77; 80.2%), Caucasian (n=75; 78.1%), and female (n=74; 77.1%) with a mean age of 58.5 years (±13.6 years) (range=27-84 years). The rate of prescription stimulant use in the DI cohort was significantly higher in the patients with DI (28.1% vs. 4.2%; p< 0.0001). There was no significant difference between the DI cohort and the control cohort in prescribed opioid use (61.5% vs 67.7%; p=0.365). Among cases who proceeded with the treatments prescribed by the dermatologist, patients taking stimulants were significantly less likely to experience symptom remission (18% vs. 51.9%, p=0.005).

Discussion: Our findings are supportive of a robust association between prescription stimulant use and DI. The exact role stimulants play in the pathophysiology of DI remains unclear, but it is plausible that prescription stimulants could be a risk factor, an aggravating/perpetuating factor, or a primary cause of DI. The results of this study also raise concern that continued treatment with prescription stimulants may prevent effective treatment of DI.

Conclusions/Implications: Physicians caring for patients with DI should be aware of the association between DI and prescription stimulant use, and consider discontinuing or reducing prescription stimulant use in this population. As most of these patients are seen in primary care, dermatology, and infectious disease clinics, consultation liaison psychiatrists are uniquely positioned to provide effective care to these patients in interdisciplinary settings.