Quantification of cutaneous sensory nerves and their substance P content in psoriasis

The aim of the present study was to extend our previous hypothesis that the inflammatory reaction in psoriasis is neurogenic, and that substance P mediates the inflammation. For this purpose, the pattern of neurofilament-positive sensory nerve fibers was studied and the lengths and substance P content of these fibers measured morphometrically in dermal and epidermal compartments of the psoriatic lesion, psoriatic but lesion-free skin, and control skin. The epidermis and dermis of the psoriatic lesions were significantly more densely innervated with neurofilament-positive fibers than either lesion-free psoriatic or control skin. Although substance P is known to be rapidly degraded in tissues, and its actual concentrations in the sections were unknown, there was an increase in substance P containing nerves in the psoriatic lesion, the increase being significant in the epidermal nerve fibers. No significant differences in the measured parameters were obtained between lesion-free psoriatic and control skin. These results indicate that there is an altered pattern of sensory nerves in a psoriatic plaque and that substance P may be an important mediator in the inflammatory processes that contribute either to the initiation or maintenance of a psoriatic lesion.