Page 126 - Recognizing axial spondyloarthritis - Janneke de Winter

CHAPTER SEVEN
mNY, modified New York; MRI, magnetic resonance imaging; NSAIDs, non-steroidal anti- inflammatory drugs; PGA patient global assessment of disease activity; PhGA, physician global assessment of disease activity; SD, standard deviation; SIJ, sacroiliiac joints; SJC, swollen joint count; SpA, spondyloarthritis; TJC, tender joint count; TNF, tumor necrosis factor; VAS, visual analogue score. Data presented as n (%) unless otherwise specified.
DISCUSSION
We report here the baseline demographic, clinical, laboratory, and imaging features of 51 individuals included in a prospective inception cohort study of first- degree relatives of HLA–B27–positive AS patients. This study aimed to investigate the earliest, preclinical phases of disease based on the notion that first-degree relatives of HLA–B27–positive AS patients have a significantly increased risk of developing SpA.
A first major conclusion is that at baseline 33% of first-degree relatives have clinical and/or imaging features that allow a classification of SpA according to the ASAS axial SpA and/or ESSG classification criteria. These findings are perfectly consistent with previous cross-sectional studies showing an increased risk of SpA among first-degree relatives. Remarkably, the prevalence of SpA among first- degree relatives in our study (33%) was even higher than that in reported studies (5–12%), while the mean age in our study was lower (13,18,39).
Several factors may contribute to this higher prevalence. First, first-degree relatives having clinical symptoms could be more willing to participate in our study than those without symptoms, which may lead to channeling bias. Indeed, a substantial percentage of seemingly healthy first-degree relatives reported having back pain when actively questioned about this symptom at baseline. The fact that these first-degree relatives were not investigated for or diagnosed as having axial SpA before inclusion in the study may be related either to the fact that the back pain symptoms were relatively mild or to ignorance of general physicians regarding these alarm symptoms. Second, we have defined SpA in this study using the ASAS axial SpA, ESSG, Amor, CASPAR Study Group, and modified New York criteria, while previous studies mostly used the modified New York criteria. It is now well recognized that AS defined by the modified New York criteria represents only a fraction of the total spectrum of SpA. In support of this explanation, none of the first-degree relatives fulfilled the modified New York criteria. Third, inclusion of MRI may have led to increased classification of first-degree relatives. However, only 2 of 17 first-degree relatives in our study would not have been classified without MRI (40,41).
In our study, we classified first-degree relatives according to their fulfillment of the ASAS axial SpA and/or ESSG classification criteria, and we did not diagnose SpA based on the rheumatologist’s opinion for 2 reasons. First, there are no diagnostic criteria for SpA. Second, a diagnosis based on expert opinion is subjective and has large intra- and interobserver variation and therefore is not
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