SAT0302 Spinal involvement in axial psoriatic artritis is not determined by the presence of HLA-B27. Is the HLA-B27 arm of the axial SPA criteria reliable for classifying axial psoriatic arthritis?
Authors: J.L. Fernandez-Sueiro, J. Pinto Tasende, S. Pertega Diaz, E. Gonzalez, I. Rego Perez, F. Blanco
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> There is a debate whether axial psoriatic arthritis (axPsA) is an ankylosing spondylitis with psoriasis, however due to the fact that PsA has characteristic clinical features, this concept is debatable. On the other hand HLA-B27 is a key component of the clinical arm of the new ASAS criteria for axial SpA <h3>Objectives</h3> To determine the prevalence of HLA-B27 in PsA and to analyze its prevalence according to the clinical forms <h3>Methods</h3> Cross-sectional prevalence study of HLA-B27. HLA-B27 was determined in the following populations: a) healthy controls (HC) (n=308) and AS (n=106) (1), b) cutaneous psoriasis (n=113), c) PsA (n=172). axPsA was defined according to our previous definition (2,3). HLA-B27 was determined wit a commercial kit: Invitrogen®, Allset Gold B27 Low and High Res SSP. For each group of patients, HLA-B27 prevalence was determined, together with its 95% confidence interval. Using data from the Galician population as reference, prevalence ratio and odds ratio values were estimated from a logistic regression model. Comparisons among groups were performed by using the Mann-Whitney U, chi-squared and Fisher’s exact tests. <h3>Results</h3> The prevalence of HLA-B27 was: HC 9,4%, AS 94,3% (p&lt;0,001), cutaneous psoriasis 9,7% (p=0,921), PsA whole group 14,5% (p=0,099), peripheral PsA 8,2% (p=0,708), axPsA (mixed/“pure”) (n=68) 23,5% (p=0,002), axPsA “mixed” (n=61) 18% (p=0,052), axPsA (pure) (n=7) 71,4% (p≤0,001),]] HLA-B27+ PsA patients had a diagnosis of the disease at an earlier age, 39,2±14,14 vs 45,3±13,52 years (p=0,036). Comparing axPsA (mixed/“pure”) HLA-B27– (n=52) vs HLA-B27+ (n=16) there were no significant differences in the following: epidemiological, clinical, metrological, inflammatory, function and structural damage assessed by BASRI. The only exception was the occiput to wall distance (1,1 cm vs 4,7 cm; p=0,036) <h3>Conclusions</h3> The prevalence of HLA-B27 in PsA is similar to the general population. HLA-B27+ seemed to determine the age of presentation of PsA. There seems to be two populations with spinal involvement in axPsA, HLA-B27+/–, being the most prevalent the HLA-B27–. These data question the hypothesis that axPsA is a primary AS and question the reliability of HLA-B27 for classifying axPsA patients using the new ASAS criteria for axial SpA Finance with a grant from: Instituto de Salud Carlos III, FIS PI080789 <h3>References</h3> Fernández-Sueiro JL, et al. Prevalence of HLA-B27 and subtypes of HLA-B27 associated with ankylosing spondylitis in Galicia, Spain Clin Exp Rheumatol. 2004, 4:465-8 Fernández-Sueiro JL, et al. Evaluation of ankylosing spondylitis spinal mobility measurements in the assessment of spinal involvement in psoriatic arthritis.Arthritis Rheum. 2009 Feb 26;61:386-392. Fernández-Sueiro JL, et al. Validity of the BASDAI for the evaluation of disease activity in axial psoriatic arthritis. Arthritis Care Res 2010 Jan 15;62:78-85. <h3>Disclosure of Interest</h3> None Declared