Investigation of pain sensitivity in individuals with shoulder pain

Abstract

Background: Shoulder pain is a common musculoskeletal (MSK) complaint associated with a significant impact on health and socioeconomic outcomes. Currently, there is a poor and conflicting evidence on the mechanisms driving shoulder pain experience. Review of the literature highlighted several methodological issues among previous cross-sectional studies, which investigated the contribution of peripheral and central sensitization in patients with shoulder pain. Particularly, the confounding role of psychological, social, and lifestyle factors (sleep, and physical activity) on the measures of sensitization were not taken into account. Therefore, research improving the knowledge about the mechanisms behind variability in shoulder pain experience would help to plan better management strategies for improving clinical outcomes. Aim: The overall aim of the thesis was to establish the role of peripheral and central sensitization in explaining shoulder pain experience. This thesis involves a systematic review and three original investigations: a parallel-group cross-sectional study, a prospective study, and a methodological investigation. Methods: The systematic review established the level of evidence of the relationships between psychological, social, physical activity, and sleep measures and measures of sensitization in individuals with MSK pain. Study-1: A parallel-group cross-sectional study investigated the presence of sensitization in patients with shoulder pain. Study-2 investigated the cross-sectional and prospective predictive relationships of measures of sensitization on shoulder pain outcomes. Study-3 investigated the concurrent validity of sensitivity to movement-evoked pain (SMEP) procedure, a novel, functional form of pain sensitivity testing against other measures of sensitization (i.e. quantitative sensory testing). Results: The systematic review identified a moderate level of evidence supporting the negative relationships between depression and pain catastrophizing and quantitative sensory testing (QST) measures among individuals with musculoskeletal pain. Particularly in shoulder pain, depression and pain catastrophizing have significant (small to fair) associations with QST measures with level of evidence ranged from ‘very low’ to ‘low’. Study-1 demonstrated mechanical allodynia, greater symptomology related to central sensitization, and greater SMEP when compared to healthy controls. Study-2 identified measures of sensitization were independently associated with worse shoulder pain outcomes at both baseline and follow-up. Sub-study: SMEP has demonstrated significant associations with measures of sensitization (i.e. QST). Conclusion: The thesis established that sensitization explains shoulder pain experience; however, it is confounded by psychological factors. This thesis also established the validity of SMEP, as a valid way of evaluating pain sensitivity in individuals with chronic shoulder pain.