Central Hypersensitivity in Patients With Subacromial Impingement Syndrome

Abstract Paul TM, Soo Hoo J, Chae J, Wilson RD. Central hypersensitivity in patients with subacromial impingement syndrome. Objective To investigate the presence of primary and secondary hyperalgesia among subjects with chronic subacromial impingement syndrome (SIS) compared with pain-free controls. Design Cross-sectional design. Setting Outpatient rehabilitation clinic, urban, academic medical center. Participants Volunteer sample (N=62) (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/nondominant 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 sex, a known confounder of PPTs. Results After adjusting for sex, subjects with SIS had significantly lower PPTs than did controls at all locations. Controls had a 1.4kg/cm2 (95% confidence interval [CI], 1.2–1.5) higher PPT at their affected shoulder than did those with SIS, a 0.7kg/cm2 (95% CI, 0.5–0.9) higher PPT at their nonaffected shoulder, and a 1.1kg/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 the level of applied pressure. Conclusions This study provides further evidence that patients with SIS have significantly lower PPTs than do 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.