Microdialysis documents changes in the micromilieu of psoriatic plaques under continuous systemic therapy

Microdialysis is a novel technique suitable to analyse soluble mediators in the skin compartment. We applied this methodical approach to monitor changes in the micromilieu of psoriatic plaques under therapy. Tissue fluid was collected from lesional and non-lesional skin of three patients with severe plaque-type psoriasis prior to as well as after 12 weeks of continuous oral therapy with fumaric acid esters. Concentrations of a spectrum of cytokines and adipokines were measured using a commercial fluorescent bead immunoassay. The procedure was well tolerated even without local anaesthesia. Prior to initiation of therapy, we found elevated levels for IL-2, IL-6, IL-18, IL-23, and resistin in lesional versus non-lesional skin, whereas adiponectin levels were higher in non-lesional skin. All patients showed significant clinical improvement under treatment, paralleled by reduced concentrations of IL-6, IL-18, IL-23, and resistin, but not IL-2 and adiponectin in lesional skin. Thus, we were able to demonstrate through microdialysis a shift in the micromilieu of psoriatic plaques, characterized by reduced levels of pro-inflammatory mediators in three patients under effective systemic anti-inflammatory therapy with fumaric acid esters. Our observations need to be confirmed by larger studies. This approach is limited by practical aspects as it is very time-consuming, but suitable to directly explore pathomechanisms causing the psoriatic phenotype in general and insulin resistance in the skin compartment in particular.