Few patient characteristics of men and women with nonradiographic axial spondyloarthritis (nr-axSpA) appear to differ, yet women with the condition have a significantly lower response rate to treatment with tumor necrosis factor (TNF) inhibitors, according to results from a prospective cohort study.
Despite these similarities between the sexes, first author Regula Neuenschwander of the department of rheumatology at Zurich University Hospital and colleagues reported in Arthritis Research & Therapy that women treated with a TNF inhibitor were 81% less likely than men to have a 40% or greater improvement on Assessment of Spondyloarthritis International Society (ASAS) response criteria by 1 year. Statistically significant differences at baseline included women's longer time to nr-axSpA diagnosis, slightly lower HLA-B27 positivity rate, higher mean baseline Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) score, higher rate of current enthesitis, and lower mean body mass index (BMI).
With radiographic disease, women have been reported to more often "present with higher self-reported disease activity and functional impairment, a lower quality of life, less severe spinal radiographic changes, and more peripheral disease (arthritis and enthesitis)," whereas men more often have "objective markers of inflammation, such as elevated C-reactive protein (CRP) levels and magnetic resonance imaging (MRI) inflammation of the axial skeleton," the researchers wrote. Radiographic disease also tends to occur more often in men, and some studies have reported men to have a greater response to TNF inhibitors. However, the current study sought to understand whether these differences between sexes exist in patients with nonradiographic disease.
The researchers included 495 patients (231 men and 264 women) with a clinical diagnosis of nr-axSpA in the Swiss Clinical Quality Management cohort during 2005-2018 who fulfilled ASAS classification criteria for axSpA and lacked definite radiographic sacroiliac joint changes according to the modified New York criteria. The radiographs were centrally digitized and independently scored in a blinded manner by a rotating group of two readers (out of six total).
Both women and men had a mean age of around 28 years at symptom onset, but women had a significantly longer diagnostic delay of 6.0 years vs. 4.7 years. Also, women were significantly less likely to be HLA-B27 positive (67.0% vs. 76.5%) and had a significantly higher mean BASDAI score at baseline (5.3 vs. 4.6). More women than men also showed signs of current enthesitis (79.6% vs. 64.0%), and women had a lower mean BMI (24.3 vs. 25.7 kg/m2). Concomitant clinically diagnosed fibromyalgia was higher in women than in men (13.1% vs. 2.7%), and when patients with fibromylagia (n = 25) were excluded the remaining differences in BASDAI were mainly because of fatigue and enthesitis, both of which occurred more often in women than in men.
A total of 163 patients without fibromyalgia started a first TNF inhibitor, and 120 had a follow-up visit at 1 year. An ASAS40 response is defined as 40% improvement in at least three of four domains on the ASAS response criteria: patient global assessment of disease activity for the past week, patient assessment of back pain over the past week, function (as assessed on the Bath Ankylosing Spondylitis Functional Index [BASFI]), and inflammation (mean of BASDAI questions 5 and 6). An ASAS40 response was achieved by 17% of women and 38% of men (odds ratio, 0.34; 95% confidence interval, 0.12-0.93), and this difference became more pronounced after adjustment for baseline differences in BASDAI, Maastricht Ankylosing Spondylitis Enthesitis Score, BMI, and diagnostic delay (OR, 0.19; 95% CI, 0.05-0.61). ASAS40 response rates were lower for patients with higher BMI but better for those with higher BASDAI levels. The researchers found comparable results when they excluded patients who stopped a TNF inhibitor because of other reasons for discontinuation and also when they counted patients who discontinued the TNF inhibitor because of remission as responders.
The sex difference in nr-axSpA patients' treatment response to TNF inhibitors was even larger than the 56% lower odds the same group of researchers reported finding between women and men with radiographic disease in an earlier report, according to the new paper.
Given that this study and others in nr-axSpA patients have found higher remission rates to TNF inhibitor therapy in men versus women, the "current study therefore adds to available data to support the claim for future randomized controlled trials in axSpA to be sufficiently powered to detect potential sex differences," the researchers said.
The authors acknowledged that a lack of MRI scans available for central scoring made it impossible to evaluate potential imaging misinterpretation, such as possible abnormalities mimicking mild sacroiliitis that have been reported to be more prevalent in women. It is also possible that some patients with fibromyalgia were missed because of screening for the condition by expert opinion of the treating rheumatologist "on a comorbidity questionnaire and not through fulfillment of classification criteria for fibromyalgia or via the use of a standardized fibromyalgia questionnaire," they said.
The study was funded by the Stiftung für Rheumaforschung in Zurich. The Swiss Clinical Quality Management Foundation is supported by the Swiss Society of Rheumatology and by 11 pharmaceutical companies. Two study authors reported receiving consulting and/or speaking fees from some of those same companies.
SOURCE: Neuenschwander R et al. Arthritis Res Ther. 2020;22(1):233.
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