Sleep disturbance in frozen shoulder: Disentangling pain-related sleep disturbance and sleep dysfunction with sensitivity and cognitive assessments

Background Sleep disturbance is a prominent feature of frozen shoulder (FS), frequently driven by nocturnal pain. However, it remains unclear whether such problems primarily reflect pain-related sleep disturbance (PRSD) or intrinsic insomnia and how each relates to pain sensitivity and cognitive–psychological factors. The aim of this study was to characterize sleep disturbances by classifying PRSD and insomnia-related symptoms (IS) in patients with FS, to provide clinically useful information, and to delineate their respective associations with pain sensitivity and pain-related psychological factors. Methods Using a prospective cohort design, 52 patients with FS were assessed for PRSD and insomnia-related symptoms (IS) using the Athens Insomnia Scale, quantitative sensory testing (pressure pain threshold, temporal summation [TS], and conditioned pain modulation [CPM]), and validated pain-related questionnaires. Patients were classified by the presence of PRSD and/or IS, and two-way ANOVA was used to test potential interactions. Results PRSD was observed in 55.8% and IS in 57.7% of the recruited patients, with 73.1% experiencing at least one form of disturbance. PRSD was associated with greater pain intensity and impaired TS and CPM, suggesting altered pain modulation. Conversely, IS was linked to higher Central Sensitization Inventory and Fremantle Shoulder Awareness Questionnaire scores and elevated anxiety and depression. Patients with comorbid PRSD and IS exhibited the most adverse profiles, with a significant interaction for TS on the affected side (p = 0.007). Conclusion PRSD and insomnia are highly prevalent in FS. They are mechanistically distinct yet synergistic in amplifying pain sensitivity. Differentiating these disturbances is crucial, as their coexistence may worsen prognosis and requires tailored multimodal management.