1948 The Journal of Rheumatology 2014; 41:10; doi:10.3899/jrheum.131462 Personal non-commercial use only. The Journal of Rheumatology Copyright © 2014. All rights reserved. Is HLA-B27 Increased in Patients Diagnosed with Undifferentiated Arthritis? Results from the Leiden Early Arthritis Cohort Floris van Gaalen, Rosaline van den Berg, Inge Verhoog, Joris Schonkeren, Annette van der Helm-van Mil, Tom Huizinga, and Désirée M. van der Heijde ABSTRACT. Objective. Undifferentiated arthritis (UA) is a common form of arthritis. According to the Assessment of Spondyloarthritis international Society (ASAS) criteria for peripheral spondy- loarthritis (pSpA), HLA-B27 can be used to help classify patients with pSpA. We tested whether HLA-B27 is increased in patients diagnosed with UA. Methods. Prevalence of HLA-B27 was compared between healthy controls and patients with UA. SpA features were compared between HLA-B27-positive and -negative UA, and SpA. Results. We found 10.1% of UA (38/375) versus 7.2% (403/5584) of controls were HLA-B27-posi- tive (OR 1.5, 95% CI 1.0–2.1; p = 0.037). HLA-B27-positive patients with UA had more SpA features than HLA-B27-negative patients (mean 1.6, SD 1.0, and 0.9 SD 0.6; p < 0.001), but patients with SpA had significantly more SpA features (mean 4.5, SD 1.5; p < 0.001). Family history and preceding infection were features more common in HLA-B27-positive than in HLA-B27-negative UA (15.8% vs 1.3%, p = 0.04 and 15.8% vs 2.6%, p = 0.04). After HLA-B27 testing, 21 additional patients (5.6%) with UA could potentially have been classified with pSpA according to the ASAS criteria. Conclusion. HLA-B27 is more common in patients with UA than in controls. However, the yield of HLA-B27 testing in UA is low. Our results suggest that HLA-B27 testing should be reserved for patients with additional SpA features. (First Release Aug 15 2014; J Rheumatol 2014; 41:1948–51; doi:10.3899/jrheum.131462) Key Indexing Terms: HLA-B27 GENETIC RISK FACTORS SPONDYLOARTHRITIS UNDIFFERENTIATED ARTHRITIS From the Department of Rheumatology, Leiden University Medical Centre, Leiden, the Netherlands. The work of F. van Gaalen is supported by Tracer, a Centre for Translational Molecular Medicine project. F. van Gaalen, MD, PhD; R. van den Berg, MSc; I. Verhoog, BSc; J. Schonkeren, BSc; A. van der Helm-van Mil, MD, PhD; T. Huizinga, MD, PhD; D.M. van der Heijde, MD, PhD, Department of Rheumatology, Leiden University Medical Centre. Address correspondence to Dr. F. van Gaalen, Department of Rheumatology, Leiden University Medical Centre, C4-R, PO Box 9600, Leiden 2300 R, The Netherlands. E-mail: f.a.van_gaalen@lumc.nl Accepted for publication June 18, 2014. Spondyloarthritis (SpA) refers to a group of common related rheumatic diseases, including ankylosing spondylitis, psoriatic arthritis, reactive arthritis, inflammatory bowel disease (IBD)-related spondylitis and arthritis, and undiffer- entiated SpA. The clinical presentation of SpA is hetero- geneous, and no single distinguishing feature exists for all forms of SpA 1 . However, various clinical laboratory and imaging features suggestive of SpA are known and form the building blocks for classification criteria for SpA and diseases in the SpA spectrum. SpA can be distinguished by its clinical presentation as predominantly axial SpA (axSpA; e.g., inflammation of the spine and/or sacroiliac joints) or peripheral SpA (pSpA; e.g., arthritis, dactylitis, and/or enthesitis) and classified with 2 criteria sets developed by the Assessment of Spondylo- Arthritis international Society (ASAS). In patients with early arthritis, the ASAS pSpA criteria performed well with a good specificity at a reasonable sensitivity 2 . According to the ASAS criteria for pSpA, HLA-B27 can be used to help classify patients with pSpA 3 . While in adults HLA-B27 is better known for its association with axSpA rather than pSpA 4 , we recently showed that in a large cohort of patients presenting with arthritis, HLA-B27 was signifi- cantly more common in patients with SpA than in patients without SpA 2 . Undifferentiated arthritis (UA) is defined as an inflam- matory arthritis in which no definitive diagnosis can be made. Inception cohorts from Europe and North America have shown that UA is common and may even be seen more frequently than rheumatoid arthritis (RA). Estimates of the percentage of patients diagnosed with UA range from 23% to 81% of early arthritis cohorts 5 . UA spans a wide spectrum of conditions with various natural courses. Some patients will have a benign, self-limiting disease course while others will experience disease persistence including development of destructive arthritis 6 . There are limited data on the preva- www.jrheum.org Downloaded on January 10, 2022 from