Objective To investigate the presence of primary and secondary hyperalgesia among subjects with chronic subacromial impingement syndrome (SIS) compared to pain-free controls. Design Cross-sectional design. Setting Outpatient rehabilitation clinic, urban, academic medical center. Participants Volunteer sample of 62 subjects (31 with SIS, 31 controls). Interventions Not applicable. Main Outcome Measures Pressure-pain thresholds (PPTs) were measured at the middle deltoid of the affected/dominant arm (primary or secondary hyperalgesia) and the middle deltoid and tibialis anterior of the unaffected/non-dominant side (secondary hyperalgesia) in SIS and healthy controls, respectively. Differences in PPTs were analyzed by Wilcoxon Rank Sum test and with linear regression analysis controlling for gender, a known confounder of PPTs. Results After adjusting for gender, subjects with SIS had significantly lower PPTs than controls at all locations. Controls had a 1.4 kg/cm2 (95% CI 1.2 – 1.5) higher PPT at their affected shoulder than those with SIS, a 0.7 kg/cm2 (95% CI 0.5 – 0.9) higher PPT at their non-affected shoulder, and a 1.1 kg/cm2 (95% CI 1.1 – 1.2) higher PPT at their contralateral tibialis anterior. Observers were not blinded to patient groupings but were blinded to level of applied pressure. Conclusion This study provides further evidence that SIS patients have significantly lower PPTs than controls in both local and distal areas from their affected arm consistent with primary and secondary hyperalgesia, respectively. Data suggest the presence of central sensitization among subjects with chronic SIS.

Objective This study aimed to examine the association of hemiplegic shoulder pain with central hypersensitivity through pressure-pain thresholds (PPT) at healthy, distant tissues. Design This study is a cross-sectional study. A total of 40 patients (n=20 hemiplegic shoulder pain (HSP), n=20 stroke without HSP) were enrolled in this study. Pressure-pain thresholds were measured at the affected deltoid and contralateral deltoid and tibialis anterior using a handheld algometer. Differences in PPTs were analyzed by Wilcoxon Rank Sum test and with linear regression analysis controlling for gender, a known confounder of PPTs. Results Subjects with hemiplegic shoulder pain had lower local PPTs than stroke control subjects when comparing the painful to dominant shoulders and comparing the non-painful shoulder and tibialis anterior to the non-dominant side controls. Similarly, those with hemiplegic shoulder pain had lower PPTs when comparing to controls in contralesional-to-contralesional comparisons as well as ipsilesional-to-ipsilesional comparisons. Conclusions Subjects with hemiplegic shoulder pain have lower local and distal PPTs than subjects without hemiplegic shoulder pain. Our study suggests that chronic shoulder pain may be associated with widespread central hypersensitivity, which has been previously found to be associated with other chronic pain syndromes. This further understanding can then help develop better treatment options for those with this hemiplegic shoulder pain.