Assessment of Neuropathic Pain in Ankylosing Spondylitis: Prevalence and Characteristics

INTRODUCTION: Pain in ankylosing spondylitis is currently considered an inflammatory pain (IP). However, it was found that some patients still had the sensation of pain even without inflammation. Our study was to investigate the prevalence and characteristics of neuropathic pain (NeP) in Chinese Han ankylosing spondylitis (AS) patients. METHODS: The study consisted of three parts. Firstly, we assessed the prevalence and clinical data of NeP in 182 AS patients. Secondly, we evaluated pain improvement after etanercept therapy in 63 patients. Finally, serum neurotransmitters were measured for 20 AS patients and ten healthy controls (HC). RESULTS: Out of 182 AS patients, our study showed that 14 patients (7.70%) had likely NeP and 55 (30.21%) had uncertain NeP. There were significant differences among the three groups with respect to nocturnal pain (NP), peripheral pain (PP), total back pain (TBP), BASDAI, ASDAS-CRP, HAD-A, HAD-D, and BASDAI-fatigue except fort CRP concentrations. Principal component analysis (PCA) of AS pain revealed that the weight of NeP was greater than PP in the first principal component (0.703 vs. 0.639). Structural equation modeling (SEM) revealed that NeP altered disease activity (β = 0.62, P < 0.001), which influenced psychological status (β = 0.42, P < 0.001). Of 63 patients who used etanercept for 3 months, significant improvement was found in NP, TBP, and PP (all P < 0.0001) but not in PDQ (10.60 ± 6.85 vs. 9.98 ± 6.40, P = 0.0671). Serum norepinephrine concentrations in patients with PDQ > 19 were higher than those in patients with PDQ ≤ 19 and HC. CONCLUSIONS: We conclude that NeP contributes to pain in AS patients.