Characterisation of Pain in Patients With Musculoskeletal Disease: a Prospective, Longitudinal, Observational Study With an Embedded Feasibility Window of Opportunity Sleep Study

BACKGROUND AND RATIONALE Pain and sleep share a complex bidirectional relationship. In both laboratory and clinical settings, pain demonstrates circadian rhythmicity and sensitivity to sleep deprivation. Poor sleep aggravates pain, and increasing pain worsens sleep disturbance, creating a potentially self-perpetuating cycle that may contribute to the development and maintenance of chronic pain. However, the mechanisms by which sleep deprivation increases pain remain unclear, particularly in the context of fibromyalgia.

One proposed mechanism involves kinesiophobia (fear of movement), which is central to the Fear Avoidance Model of chronic pain. This model proposes that excessive fear of movement, due to the expectation that moving will cause pain, prevents people from engaging in beneficial physical activities. This avoidance leads to physical deconditioning, which further amplifies pain by reducing the engagement of endogenous descending pain control mechanisms. Understanding the mechanistic link between sleep, pain, and physical activity is particularly important in fibromyalgia, a debilitating chronic pain condition characterised by widespread pain, poor sleep, fatigue, and reduced motivation.

Polysomnography studies in fibromyalgia have demonstrated specific EEG correlates of sleep fragmentation, including alpha intrusion into slow-wave sleep, which may reflect non-restorative sleep. Observational and laboratory studies have shown behavioural changes consistent with kinesiophobia in this population. Previous research by our group has found that 73% of fibromyalgia patients fulfil criteria for clinical insomnia, with strong correlations between sleep disturbance and pain severity (R=0.44; P<0.001), fear of movement (R=0.38; P<0.001), and quality of life measures (R=0.51; P<0.001). Additionally, patient partners have explicitly identified poor sleep as a barrier to participating in physical rehabilitation and regular exercise, both of which are mainstays of fibromyalgia treatment.

RATIONALE FOR DIGITAL CBT-I Recent systematic reviews suggest that cognitive behavioural therapy for insomnia (CBT-I) is associated with significant improvements in self-reported sleep quality, pain, and depression in chronic pain populations. However, existing research has important limitations: (1) it has not focused on physiological measures of sleep and activity, (2) quantitative measures of motor performance and pain have not been assessed, (3) the mechanisms by which CBT-I affects pain and physical activity remain unknown, and (4) most studies have used in-person CBT-I, which has variable delivery and limited accessibility.

Digital CBT-I (dCBT-I) addresses these limitations. It removes inter-therapist variability, ensuring consistent treatment delivery, and overcomes access barriers such as therapist shortages, long waiting lists, and travel difficulties. Sleepio, the dCBT-I program used in this study, has demonstrated effectiveness for sleep disturbance and cognitive symptoms in insomnia and has NICE accreditation.