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Responses to Intradermal Injections of Substance P in Psoriasis Patients with Pruritus

Background: Various mediators have been suggested for the pathogenesis of pruritus in psoriasis. Methods: To investigate cutaneous responses of substance P in pruritic lesional and nonlesional areas of psoriasis patients and in healthy controls, substance P, saline and histamine were injected intradermally. After each injection, pruritus, flare and wheal were recorded. Results: There was no statistical difference in the latency period, duration, area under the curve and maximum intensity of pruritus evoked by substance P (10–5 and 10–6 mol/l) between psoriasis and healthy control skin. Substance P (10–5 mol/l) induced a tendency to a greater intensity of pruritus in lesional compared to nonlesional psoriatic skin (p = 0.08). Histamine produced a shorter itch latency period (p < 0.05) and a lower maximum intensity of pruritus (p = 0.05) in lesional psoriasis skin than in healthy control skin. No significant difference in flare area was observed between the psoriasis patients and healthy controls. The histamine-induced wheal was smaller in psoriasis patients than in healthy individuals (p < 0.05). Conclusion: Intradermally injected substance P induced pruritus, flare and wheal in psoriasis patients. However, these responses did not differ significantly from those of the healthy controls.