Evaluation of the Association of Serum Substance P Levels With Neuropathic Pain, Central Sensitization, Disease Severity, and Quality of Life Across Different Treatment Groups in Patients With Chronic Plaque Psoriasis

Psoriasis is a chronic, immune-mediated inflammatory skin disease characterized by complex interactions between immune pathways, cutaneous inflammation, and the nervous system. In addition to visible skin lesions, patients may experience pruritus, pain, burning, tingling, and other sensory complaints that can substantially impair quality of life. Increasing evidence suggests that neuroimmune mechanisms may contribute to these symptoms. Substance P, a neuropeptide involved in neurogenic inflammation, nociception, and pruritus, may represent one of the mediators linking cutaneous inflammation with sensory symptoms in psoriasis. The IL-17 pathway may also interact with neuroimmune mechanisms involved in pain and pruritus.

This single-center, cross-sectional, observational study aims to investigate the relationship between serum Substance P levels and clinical features including neuropathic pain characteristics, central sensitization, psoriasis severity, pain intensity, pruritus intensity, and dermatology-related quality of life in adults with chronic plaque psoriasis. The study will also explore whether serum Substance P levels and clinical characteristics differ according to the patients current treatment approach.

Approximately 100 patients with chronic plaque psoriasis will be enrolled and evaluated in three treatment groups: patients receiving IL-17 inhibitor therapy, patients receiving conventional systemic therapy such as methotrexate or acitretin, and patients receiving topical therapy only or no current treatment. Treatment history and duration of current therapy will also be recorded.

Psoriasis severity will be assessed using the Psoriasis Area and Severity Index (PASI), and quality of life will be evaluated using the Dermatology Life Quality Index (DLQI). Pain and pruritus intensity will be recorded using Numeric Rating Scales (NRS), and central sensitization symptoms will be evaluated using the Central Sensitization Inventory (CSI).

The presence and localization of pain will be recorded, including whether the pain is associated with psoriatic plaques. In participants reporting pain, neuropathic pain characteristics will be assessed using the Douleur Neuropathique 4 Questions (DN4). DN4 scores will be recorded both as total scores and according to the validated cutoff, with scores of 4 or higher considered positive for neuropathic pain features. Participants without pain will not undergo DN4 assessment.