Page 114 - Recognizing axial spondyloarthritis - Janneke de Winter

CHAPTER SEVEN
subjects were ages 18–40 years, since new onset of SpA after age 45 years is rare and since the major objective was to study development rather than incidence of SpA. We included all seemingly healthy first-degree relatives, indicating that first- degree relatives 1) were not diagnosed as having SpA at the time of the baseline visit, 2) were not treated for musculoskeletal symptoms by a physician, and 3) may or may not have had musculoskeletal symptoms at the time of the baseline visit when actively questioned about those symptoms. We selected HLA–B27–positive probands with established AS rather than SpA as a whole spectrum for 3 reasons. First, we aimed for a high entry threshold by only including HLA–B27–positive AS patients, thereby avoiding as many misdiagnosed probands as possible. Second, genetic risk factors other than HLA–B27 have largely only been established in AS and not in other SpA subtypes (20). Finally, HLA–B27–positive patients tend to have more ankylosis than HLA–B27–negative patients (21), thereby possibly favoring the presence and detection of structural radiographic changes in their first-degree relatives.
HLA–B27–positive probands with AS from our dedicated SpA outpatient clinic were systematically and consecutively asked by their treating rheumatologists to inform their first-degree relatives about this cohort study both verbally and by letter. The research physician actively contacted the proband to determine whether the first-degree relatives were interested. To increase the sample size further, an interview with one of the research physicians was published in a journal of the Dutch AS association. In this interview, we requested AS patients to inform their first-degree relatives. Thereafter, we followed the same procedure as described above. Of note, probands did not participate in the study. All first-degree relatives signed informed consent prior to any study procedures. Major exclusion criteria were the presence of already diagnosed SpA, other rheumatic conditions including fibromyalgia, and back pain due to other known conditions such as intervertebral disc degeneration and back injury. All study procedures were done in compliance with the Helsinki Declaration. The study protocol was approved by the Medical Ethics Committee of the Academic Medical Center/University of Amsterdam.
Clinical evaluation at baseline
Data on demographics (sex, age, and race), medical and family history, and the use of medication were recorded. History specific for SpA-related features included back pain, IBP as defined by the Assessment of SpondyloArthritis international Society (ASAS) criteria (22), peripheral arthritis, enthesitis, dactylitis, psoriasis, inflammatory bowel disease (IBD), and uveitis, all diagnosed by a physician. Disease activity was measured by physician’s global assessment of disease activity and patient’s global assessment of disease activity on a visual analog scale (VAS), patient’s nocturnal pain on a VAS, the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) (23), and the Ankylosing Spondylitis Disease Activity Score using the C-reactive protein level (ASDAS-CRP) (24). Function was assessed by the Bath Ankylosing Spondylitis Functional Index (BASFI) (25). Clinical
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