Exploration of the clinical course and longitudinal correlations in frozen shoulder : the role of autonomic function, central pain processing, and psychological variables: a longitudinal multicenter prospective observational study

Abstract: Background Altered central pain processing (CPP) and dysautonomia might play a role in the clinical course of frozen shoulder and psychological factors, like pain catastrophizing and hypervigilance, might influence clinical variables in frozen shoulder. Objectives To explore the clinical course of frozen shoulder regarding CPP, dysautonomia, pain catastrophizing, and hypervigilance and to explore whether longitudinal correlations between these outcomes and pain intensity were present. Design prospective longitudinal observational study. Method Participants with frozen shoulder were recruited at hospitals and general practitioner practices and followed for 9 months. They completed six questionnaires (about demographics, shoulder pain and disability, pain intensity, pain catastrophizing, pain hypervigilance, and autonomic symptoms) and underwent tactile sensitivity (allodynia), pressure pain thresholds (hyperalgesia), temporal summation, and conditioned pain modulation during four timeframes (3-month intervals). Results Initially, 149 participants with frozen shoulder were recruited and 88 completed all the measurements. An improvement from baseline to at least one follow-up measurement was found for shoulder pain and disability, pain intensity, pain catastrophizing, hypervigilance, and dysautonomia. A fair longitudinal correlation was found between pain intensity and catastrophizing and hypervigilance (r\ua0=\ua00.301\u20130.397). Poor longitudinal correlations were found between pain intensity and allodynia and hyperalgesia (r\ua0=\ua0 120.180-0.193), between pain catastrophizing and dysautonomia (r\ua0=\ua00.209) and between hypervigilance and hyperalgesia (r\ua0=\ua0 120.159). Conclusion Patients with frozen shoulder showed an early improvement that flattened with time in several pain and psychological variables over the course of 9 months. However, autonomic symptoms rather showed a late improvement over 9 months