Recent reports suggest deficits in conditioned
pain modulation (CPM) and enhanced suprathreshold heat
pain response (SHPR) potentially play a role in the development of
chronic pain. The purpose of this study was to investigate whether central
pain processing was altered in 2 musculoskeletal
shoulder pain models. The goals of this study were to determine whether central
pain processing: 1) differs between healthy subjects and patients with clinical
shoulder pain; 2) changes with induction of exercise-induced
muscle pain; and 3) changes 3 months after shoulder surgery. Fifty-eight patients with clinical
shoulder pain and 56 age- and sex-matched healthy subjects were included in these analyses. The healthy cohort was examined before inducing
EIMP, and 48 and 96 hours later. The clinical cohort was examined before shoulder surgery and 3 months later. CPM did not differ between the cohorts, however; SHPR was elevated for patients with
shoulder pain compared to healthy controls. Induction of acute
shoulder pain with
EIMP resulted in increased
shoulder pain intensity but did not change CPM or SHPR. Three months following shoulder surgery, clinical
pain intensity decreased but CPM was unchanged from preoperative assessment. In contrast, SHPR was decreased and showed values comparable with healthy controls at 3 months. Therefore, the present study suggests that: 1) clinical
shoulder pain is associated with measurable changes in central
pain processing; 2) exercise-induced
shoulder pain did not affect measures of central
pain processing; and 3) elevated SHPR was normalized with shoulder surgery. Collectively our findings support neuroplastic changes in
pain modulation were associated with decreases in clinical
pain intensity only, and could be detected more readily with thermal stimuli.
PERSPECTIVE: Longitudinal studies involving quantitative sensory testing are rare. In exploring 2 musculoskeletal
shoulder pain models (exercise-induced
muscle pain and surgical
pain), conditioned
pain modulation was unchanged from pre- to post-assessment in both models. Suprathreshold heat
pain response decreased after shoulder surgery and was comparable to healthy controls, suggesting this measure may be sensitive to decreases in clinical
pain intensity.