Reduced sleep quality is highly prevalent and associated with physical function and cardiorespiratory fitness in patients with axial spondyloarthritis: a cross-sectional study

Objectives: To assess sleep quality, and its associations with physical function, cardiorespiratory fitness, and spinal mobility, in axial spondyloarthritis (axSpA) patients.Method: Baseline data from the Exercise for Spondyloarthritis trial were used.Assessments included [Pittsburgh Sleep Quality Index (PSQI), 0-21, 21 = worst], performance-based physical function [Ankylosing Spondylitis Performance Index (ASPI), seconds, higher = worse], patient-reported physical function [Bath Ankylosing Spondylitis Functional Index (BASFI), 0-10, 10 = worst], cardiorespiratory fitness [peak oxygen uptake (VO 2peak ), mL/kg/min, lower = worse], and spinal mobility [Bath Ankylosing Spondylitis Metrology Index (BASMI), 0-10, 10 = worst].Associations were examined in separate models using multiple linear regression.Results: Ninety-nine patients with axSpA were included, 53% female, mean age 46 years, and 72% with high disease activity (ASDAS-C-reactive protein ≥ 2.1), of whom 84 (85%) had reduced sleep quality.Sleep disturbance was most frequently reported (65%), followed by poor subjective sleep quality (53%), daytime dysfunction (41%), and increased sleep latency (41%).Positive associations were observed between PSQI and ASPI [β = 0.10, 95% confidence interval (CI) 0.01, 0.19] and PSQI and BASFI (β = 0.85, 95% CI 0.51, 1.20), and there was an inverse association between PSQI and VO 2peak (β = -0.14, 95% CI -0.27, -0.01), adjusted for age and sex.There was no association between PSQI and BASMI.Conclusion: Reduced sleep quality was common in axSpA patients with moderate to high disease activity.Better sleep quality was associated with better physical function and higher cardiorespiratory fitness.There was no association between sleep quality and spinal mobility.Trial registration: ClinicalTrials.govNCT02356874 Axial spondyloarthritis (axSpA) is an autoimmune inflammatory rheumatic disease that primarily affects the axial skeleton, and encompasses both radiographic (also termed ankylosing spondylitis) and non-radiographic axSpA (1).The disease usually debuts in early adulthood, with an equal sex distribution among patients with non-radiographic axSpA, although more men tend to develop radiographic axSpA.The leading symptoms are inflammatory back pain and morning stiffness (1).Patients also report reduced sleep quality (2).The importance of sleep in axSpA is being increasingly recognized, and since 2021 sleep has been included as an important domain for clinical trials in the Assessment of SpondyloArthritis international Society (ASAS)-Outcome Measures in Rheumatology (OMER-ACT) core domain set for axSpA (3,4).