The Segmental Distribution of Hypersensitivity in Patients With Chronic Subacromial Pain Syndrome

Shoulder pain is a common musculoskeletal pain condition in the general population, with a prevalence that has doubled in all age groups over the past 40 years, reaching 22%-30%. Despite treatment, at least 40% of patients report incomplete improvement in pain severity and duration of symptoms, which are the two main determinants of treatment response. There is convincing evidence that the persistence of pain in these patients is due to peripheral or central sensitization mechanisms. Central sensitization refers to pain hypersensitivity mainly resulting from amplifying central nervous system signals and reduced activity of central inhibitory pathways. The clinical presence of central sensitization is determined by examining specific pain characteristics or evaluating changes in pain threshold. The objective manifestation of central sensitization is a decreased pressure-pain threshold (PPT) (hypersensitivity). In previous studies using PPT measurement, pain sensitivity was detected in the shoulder and remote joints in patients with subacromial pain syndrome (SPS), which was considered as evidence of central sensitization. However, these studies did not show how pain sensitivity differs according to body segment in patients with SPS. Hypersensitivity that develops due to chronic shoulder pain would exacerbate the perception of pain caused by other musculoskeletal diseases or trauma. Therefore, it may be important for clinicians to determine how pain sensitivity varies by body segment in patients with SPS

Inclusion criteria

• To be diagnosed with chronic (≥ 3 months) unilateral SPS according to clinical examination (the Hawkins-Kennedy test and the painful arc test) and/or imaging.
• To be scored ≥ 40 on CSI

Exclusion criteria

i) Bilateral shoulder pain syndrome, ii) History ofshoulder surgery, iii) Osteoarthritis of the glenohumeral joint on direct radiography, v)concomitant diseases with the potential risk of development of central/peripheral sensitization [diseases specified in CSI part B, vi) symptomatic lateral/central spinal stenosis, myelopathy, or radiculopathy, vii) history of centrally acting drug use (e.g.,pregabalin, gabapentin, amitriptyline, duloxetine, and opioid) viii) alcohol/substance abuse.