Page 116 - Recognizing axial spondyloarthritis - Janneke de Winter

CHAPTER SEVEN
the proportion of first-degree relatives fulfilling any of the SpA classification criteria to that of first-degree relatives not fulfilling SpA classification criteria. The Mann- Whitney U test was used for continuous data. Data are presented as numbers and percentages or as the mean±SD. Statistical tests were 2-sided, and P values less than 0.05 were considered significant. A similar analysis was performed for first- degree relatives with imaging signs suggestive of SpA versus first-degree relatives without imaging abnormalities.
RESULTS
Clinical and biological features of SpA in FDRs of HLA-B27 positive AS patients
Fifty-one first-degree relatives of 36 probands (comprising 33 parents and 5 siblings) with AS were included in this analysis. Approximately 85% of the approached first-degree relatives were willing to participate in the study. The main reasons for refusing study participation were living abroad, being too busy, and fear of blood collection, and a few first-degree relatives were not interested in participating without clarifying their motivation. Twenty-seven families of the 36 probands (75%) did not have any members with SpA other than the proband. Six of the probands (17%) had 1 sibling diagnosed as having SpA, and 1 proband (3%) had 1 child diagnosed as having SpA. Five probands (14%) had a parent diagnosed as having SpA. Of the first-degree relatives of these 5 probands, 3 families had both 1 sibling (with the exception of 1 proband having 2 siblings) and 1 parent. The mean±SD age of the first-degree relatives at inclusion was 25±5 years; 25 participants (49%) were male, and 26 (51%) were HLA–B27 positive. The baseline characteristics of the study population are summarized in Table 1. Upon being asked, 29 first-degree relatives (57%) reported back pain and 11 (22%) fulfilled criteria for IBP. Of the 51 first-degree relatives, 20 (39%) reported past or present arthralgia and 1 (2%) reported past or present peripheral arthritis. None of the first-degree relatives reported past or present enthesitis or dactylitis. Of all 51 first-degree relatives, 2 (4%) had psoriasis, 1 (2%) reported IBD, none reported past or present urethritis/diarrhea, and 1 (2%) had past or present uveitis. A modified Schober test result of 4.5 cm was found in 11 first-degree relatives (22%), and 2 first- degree relatives (4%) had a chest expansion of 3.6 cm. None of the first-degree relatives had arthritis, but 8 (16%) had at least 1 tender joint. Ten participants (20%) had tenderness of at least 1 entheseal point, but none had dactylitis, nail psoriasis, or skin psoriasis. Laboratory results showed an elevated CRP level, ESR, or calprotectin level in 6 (12%), 4 (8%), and 0 (0%), respectively, of first-degree relatives.
Imaging features of SpA in first-degree relatives of HLA–B27–positive AS patients
Three first-degree relatives (6%) had low-grade sacroiliitis not fulfilling the modified New York criteria (grade I unilaterally or bilaterally, or grade II unilaterally) on SI joint radiography, and 1 (2%) had syndesmophytes on spinal radiography.
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