Delusional infestation, including delusions of parasitosis: results of histologic examination of skin biopsy and patient-provided skin specimens.

OBJECTIVE: To review the results of skin biopsies and patient-provided specimens from patients whose assessment was consistent with delusional infestation, including delusions of parasitosis.
DESIGN: Retrospective medical record review.
SETTING: Mayo Clinic, Rochester, Minnesota. PATIENTS: The study population comprised all patients who were seen at Mayo Clinic and had a diagnosis of delusional skin infestation, including delusions of parasitosis, between 2001 and 2007, and who underwent biopsies as part of their dermatologic evaluations or brought samples to their clinical consultations. MAIN OUTCOME MEASURES: The results of examination of these biopsy and patient-provided specimens.
RESULTS: A total of 108 patients met inclusion criteria for this study: 80 received biopsies, 80 had self-procured skin specimens, and 52 patients received biopsies and provided specimens. No biopsy specimen (0 of 80) provided evidence to support skin infestation. The most common interpretations in the 80 biopsy specimens were dermatitis in 49 of 80 (61%); excoriation, ulceration, or erosion in 38 (48%); and nonspecific dermal inflammation in 25 (31%). Patient-provided specimens were most frequently assessed by the physician (generally a dermatologist) evaluating the patient, although 20 of the 80 samples (25%) were submitted for pathologic evaluation. Of these 80 specimens, 10 (13%) contained insects. All but 1 of the insects were noninfesting varieties; 1 (1%) was a pubic louse. The remaining findings consisted of cutaneous debris, environmental detritus, or plant material.
CONCLUSION: In patients with suspected delusional infestation, neither skin biopsies nor examination of patient-provided specimens provided objective evidence of skin infestation.