Fatigue is one of the cardinal features of ankylosing spondylitis (AS) and contributes substantially to the disability associated with this disease. The mechanisms underlying fatigue in AS remain poorly understood, and this has hampered the development of targeted, effective treatment of this disabling feature of AS. The current study was undertaken, therefore, to investigate the brain networks underlying fatigue in AS.
Twenty patients with back pain secondary to AS (15 men and 5 women; mean ± SD age 34.8 ± 11.9 years) and 20 age- and sex-matched controls consented to participate in the study. Patients underwent clinical assessment of AS using the Fatigue Severity Scale, the Affect Intensity Measure, and the McGill Pain Questionnaire. Brain gray matter and white matter connectivity was assessed using 3T magnetic resonance imaging.
The patients with AS had significant fatigue that correlated with measures of their emotional strength and spinal mobility. Individual fatigue scores were negatively correlated with the amount of gray matter in areas of the dorsal and ventral attention networks, the somatosensory cortices, and the caudate nucleus, but were positively correlated with gray matter within the executive control network and putamen. Moreover, in patients with high fatigue scores, white matter tracts connecting these brain structures (e.g., inferior fronto-occipital fasciculi, superior/inferior longitudinal fasciculi, and corticothalamic tracts) exhibited low fractional anisotropy (indicative of decreased white matter tract integrity).
These data indicate that fatigue in AS involves sensory salience and attention brain networks.