The itch experienced in patients with delusional infestation (DI) is probably not caused by an inflammatory skin disorder but is likely to be significantly affected by psychological factors, according to study findings presented in a letter to the editor published in the Journal of the European Academy of Dermatology & Venereology.
Unidentifiable by physical examination, investigators acknowledged that DI is an extraordinary disorder (incidence estimates range from 2 to 30 per 1 million people per year). Patients may experience severe itch, believing they are infested with living or nonliving pathogens. If DI is a psychiatric disease, clinicians would not expect inflammation or cytokine release in the skin of these patients, investigators noted. Researchers sought to investigate whether patients with DI have an altered immunological response in the skin.
They conducted an observational study comparing patients (n=19) clinically diagnosed (by a panel including 1 psychiatrist and 2 dermatologists) with DI with healthy control participants (n=15). Determined in the stratum corneum (SC), levels of cytokines of different signature were collected by minimal invasive tape stripping obtained from the backs of patients between the shoulder blades — as this location is less likely to be scratched — to attenuate the possibility that long-term scratching among patients with DI may induce an inflammatory reaction and therefore a cytokine release in the skin.
Researchers found no major skin abnormalities although they did note dry skin and small excoriations in patients. The 2-sided Mann-Whitney test determined the differences in the levels of the immunological markers between patients with DI and health control participants. They included markers of itch-mediating cytokines (IL31, IL22, Th2 immunity [CCL17, CCL20]), and matrix metallopeptidase [MMP9], markers of innate immunity (IL18 and CXCL8) and Th1 immunity (CXCL10). They used a multiplex immune assay to determine stratum corneum concentrations of immunological markers.
They found no significant difference in cytokine levels between patients with DI and HC.
Researchers concluded, “The itch experienced in patients with DI is likely not caused by an inflammatory skin condition which in previous studies did show altered SC profiles of the same immunological markers.” They added, “It is therefore likely that psychological factors in particular play an important role in symptoms in patients with DI.” They suggest therapy focuses on the psychological cause with antipsychotics as the basis of treatment.
Kemperman PMJH, Vulink NCC, De Rie MA, Kezic S. Delusional infestation: it is the brain that itches and not the skin. J Eur Acad Dermatol Venereol. Published online December 22, 2022. doi:10.1111/jdv.18824