Substance P and pruritus in psoriasis

Background Pruritus is a frequent symptom that is encountered in psoriasis, and it can significantly add to the burden of the disease. Due to their frequent involvement in neurogenic inflammation, neuropeptides have been implicated in the pathogenesis of psoriasis and pruritus. Results from various studies, however, are conflicting. Objective To examine the expression of substance P (SP) mRNA in skin specimens, as well as to measure the skin and plasma levels of SP using ELISA in patients with psoriasis. The values will be correlated to each other, as well as to the severity of psoriasis and its itch. Patients and methods Thirty patients with chronic plaque psoriasis and 18 healthy controls were involved in this study. Skin expression of SP mRNA was analyzed by real-time PCR. SP levels in skin biopsies and plasma were determined using enzyme linked immunosorbent assay. We examined the levels of SP in patients with psoriasis in relation to severity of psoriasis, as represented by the Psoriasis Area and Severity Index, and pruritus intensity, as determined by the Visual Analogue Scale. Results SP mRNA expression, and tissue and plasma SP levels as well, were significantly higher in patients with psoriasis with or without pruritus in relation to controls. No significant differences were detected in SP measurements between pruritic and nonpruritic patients. SP mRNA expression correlated with Psoriasis Area and Severity Index scores, whereas tissue SP levels correlated negatively with Visual Analogue Scale scores. Conclusion SP seems to have a significant role in the pathogenesis of psoriasis irrespective of pruritus. It seems to have an indirect role, however, in psoriatic pruritus, possibly through the action of proteases. The role of SP antagonists in the treatment of psoriasis, as well the relation of SP to proteases in psoriatic pruritus are points that deserve further research.