Increased IL-23 Expression in Palmoplantar Psoriasis and Hyperkeratotic Hand Dermatitis

P atients with hyperkeratotic hand dermatitis (HHD) have chronic, sharply demarcated, fissureprone plaques on the palms and/or soles without evidence of other skin diseases such as atopic dermatitis or psoriasis. Although HHD has a distinct clinical picture, the histologic pattern of HHD is nonspecific, showing “spongiotic psoriasiform” type changes. The cause of HHD is unknown, and whether it is a chronic eczematous process or a variant of localized psoriasis is controversial. Recent evidence suggests that type 17 helper T (TH17) cells, which are CD4 T cells that produce interleukin (IL) 17A, are major contributors to psoriasis pathogenesis. Characteristically, TH17 cells express IL-23 receptors, which makes them responsive to IL-23, a cytokine that promotes survival and proliferation of TH17 cells. Although chronic psoriatic plaques have demonstrated elevated levels of IL-23, IL-23 expression has not been evaluated in palmoplantar psoriasis or HHD. Thus, we sought to compare IL-23 expression patterns in chronic plaque psoriasis, palmoplantar psoriasis, and HHD.