Predictive Model for PENS Response in Subacromial Pain Syndrome

Inclusion Criteria: Adults aged between 18 and 65 years. Clinical diagnosis of subacromial pain syndrome (SAPS), based on the following clinical criteria: * Pain localized to the anterolateral shoulder region. * Symptoms present for more than 6 weeks. * Painful arc during shoulder abduction. * Positive Neer or Hawkins-Kennedy impingement signs. * Positive Jobe (empty can) test or external rotation resistance test. Visual Analogue Scale (VAS) for shoulder pain ≥ 3/10 in the previous week. Able to understand study procedures and sign informed consent. Exclusion Criteria: * Bilateral shoulder pain. * History of fracture, dislocation, or surgical intervention on the affected shoulder. * Presence of other shoulder pathologies such as adhesive capsulitis (frozen shoulder), glenohumeral instability, or full-thickness rotator cuff tear. * Medical contraindications for PENS application (e.g., active anticoagulation, pregnancy, or decompensated psychiatric condition). * Diagnosed cervical radiculopathy or myelopathy. * Neurological or cognitive disorders interfering with study participation. * Presence of chronic widespread pain syndromes, such as fibromyalgia. * Belonephobia (severe needle phobia) that prevents intervention.