Among patients with a diagnosis of delusional skin infestation, neither biopsies nor patient-provided specimens provided objective evidence of skin infestation, according to a report posted online today that will be published in the September issue of Archives of Dermatology, one of the JAMA/Archives journals.

Delusional infestation is a condition in which patients steadfastly yet mistakenly believe that pathogens are infesting their skin. Sometimes, patients believe their skin is literally crawling with bugs, worms, or germs, which is also known as "delusions of parasitosis." In other cases, patients perceive that inanimate objects such as wood chips, fibers, or little tubes are involved. While case reports and small case series of these reports exist, there has not been much formal study of the validity of the specimens, whether derived from biopsies or provided by the patients themselves.

Sara A. Hylwa, B.S., and colleagues from the Mayo Medical School and Mayo Clinic in Rochester , Minn. conducted a retrospective review of delusional infestation cases seen at the Mayo Clinic between 2001 and 2007. Of the 108 patients included in this study, 80 received biopsies, 80 provided self-procured specimens, and 52 had both. Among the materials reported to be infesting the skin were bugs (79%), worms, eggs, fibers, "specks," "triangles," and gravel or grainlike material.

None of the biopsies showed evidence of infestation, the authors report. Sixty-one percent did reveal dermatitis and nearly half (48%) exhibited excoriation, ulceration or erosion of the skin. Of the patient-provided specimens, one-fourth of which were examined by a pathologist, only one contained an infesting parasite—a pubic louse that was determined not to be responsible for the symptoms reported.

The authors write that the results suggest that in cases of delusional infestation, biopsies may not overturn the diagnosis: "This study is important for patients. Patients frequently believe that physicians are dismissive of their concerns and are not examining their skin closely enough, and therefore patients request that more testing be performed." In conclusion, the authors note, "The majority of skin biopsy results did show dermatitis, raising the possibility that skin inflammation and its attendant tactile discomfort might be the trigger provoking delusional symptoms in susceptible individuals."