The goal of this observational study is to better understand whether blood levels of Substance P are related to pain, itching, altered pain sensations, central sensitization, psoriasis severity, and quality of life in adults with chronic plaque psoriasis.
The main questions this study aims to answer are:
Are serum Substance P levels associated with neuropathic pain features, central sensitization, psoriasis severity, pain, itching, and quality of life? Do serum Substance P levels and these clinical features differ among patients receiving different psoriasis treatments?
Researchers will compare three groups of patients: those receiving IL-17 inhibitor treatment, those receiving conventional systemic treatment with methotrexate or acitretin, and those receiving topical treatment only or no current treatment.
Participants will:
Have their psoriasis severity assessed and complete questionnaires about pain, itching, central sensitization, and quality of life.
Undergo a neurological examination. Participants who report pain will also be evaluated for neuropathic pain features using the DN4 questionnaire.
Provide a blood sample for measurement of serum Substance P and routine laboratory tests.
Undergo electromyography and nerve conduction studies if peripheral neuropathy is suspected during the neurological evaluation.
No treatment will be assigned or changed as part of this study.
Age ≥18 years
Diagnosis of chronic plaque psoriasis
Ability and willingness to provide written informed consent
For the IL-17 inhibitor group: current treatment with an IL-17 inhibitor for at least 8 weeks
Known diabetes mellitus, HbA1c ≥6.5%, or fasting plasma glucose ≥126 mg/dL
Vitamin B12 level <200 pg/mL
Known peripheral neuropathy or peripheral neuropathy detected during neurological evaluation and/or electromyography
Neuropathy related to uremia or thyroid disease
Adults with chronic plaque psoriasis who are followed at the Dermatology Department of Istanbul Training and Research Hospital and meet the study eligibility criteria will be included. Participants will be classified into three predefined groups according to their current psoriasis treatment: IL-17 inhibitor therapy, conventional systemic therapy with methotrexate or acitretin, and topical therapy only or treatment-naive. Participants will undergo clinical, patient-reported, laboratory, and neurological assessments during a single cross-sectional study period.
Cohort
Cross-sectional
IL-17 Inhibitor Therapy
Biological/VaccineExposure to IL-17 inhibitor therapy prescribed as part of routine clinical care for chronic plaque psoriasis. Treatment is not assigned, initiated, or modified by the study. Participants are classified according to their current treatment at the time of study assessment.
Conventional Systemic Therapy
DrugExposure to conventional systemic therapy with methotrexate or acitretin prescribed as part of routine clinical care for chronic plaque psoriasis. Treatment is not assigned, initiated, or modified by the study.
Association Between Serum Substance P Levels and DN4 Score
The association between serum Substance P concentration measured by ELISA and the total Douleur Neuropathique 4 Questions (DN4) score will be evaluated among participants who report pain and undergo DN4 assessment. DN4 scores range from 0 to 10, with scores ≥4 considered positive for neuropathic pain features.
Association Between Serum Substance P Levels and Central Sensitization Inventory Score
The association between serum Substance P concentration and the Central Sensitization Inventory (CSI) Part A total score will be evaluated. Part A consists of 25 items, with total scores ranging from 0 to 100. Higher scores indicate a greater burden of symptoms associated with central sensitization.
Association Between Serum Substance P Levels and Psoriasis Severity
The association between serum Substance P concentration and psoriasis severity measured by the Psoriasis Area and Severity Index (PASI) will be evaluated. PASI ranges from 0 to 72, with higher scores indicating greater disease severity.
Association Between Serum Substance P Levels and Pain Intensity
The association between serum Substance P concentration and pain intensity measured using a 0-10 Numeric Rating Scale (NRS) will be evaluated, with higher scores indicating greater pain intensity.
Differences in Serum Substance P Levels Across Treatment Groups
Serum Substance P concentrations will be compared among participants receiving IL-17 inhibitor therapy, conventional systemic therapy with methotrexate or acitretin, and topical therapy only or no previous/current systemic treatment according to the study group definitions.
Psoriasis Area and Severity Index (PASI) Score Across Treatment Groups
The Psoriasis Area and Severity Index (PASI) total score will be compared across the three predefined treatment groups. Scores range from 0 to 72, with higher scores indicating greater psoriasis severity.
Central Sensitization Inventory (CSI) Score Across Treatment Groups
The Central Sensitization Inventory (CSI) Part A total score will be compared across the three predefined treatment groups. Part A consists of 25 items, with total scores ranging from 0 to 100. Higher scores indicate a greater burden of symptoms associated with central sensitization.
Dermatology Life Quality Index (DLQI) Score Across Treatment Groups
The Dermatology Life Quality Index (DLQI) total score will be compared across the three predefined treatment groups. Total scores range from 0 to 30, with higher scores indicating greater impairment of dermatology-related quality of life.
Neurological Sensory Symptoms and Sensory Examination Findings
The presence of sensory symptoms including burning, stinging, electric shock-like sensations, tingling, numbness, pins and needles, pain associated with itching, pain evoked by touch, and sensitivity to heat or cold will be recorded. Sensory examination findings including vibration sensation, pinprick sensation, allodynia, and hyperalgesia will also be documented during the neurological examination. The frequency and distribution of these symptoms and examination findings will be evaluated.
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