PREVALENCE OF SPONDYLARTHROPATHIES IN HLA-B27 POSITIVE AND NEGATIVE BLOOD-DONORS

Objective. To determine the overall prevalence of spondylarthropathy ( SpA) among whites. Methods. To screen for SpA symptoms, such as inflam matory back pain (IBP), joint swelling, psoriasis, and uveitis, or a s pecific family history, questionnaires were mailed to 348 blood donors (174 HLA-B27 positive and 174 HLA-B27 negative), From the responding 273 persons (78%; 140 B27 positive, 153 B27 negative), 126 were select ed for further evaluation based on the symptoms reported, Of this grou p, 90 persons agreed to undergo physical examination (71.4%; 46 B27 po sitive, 44 B27 negative), There was no difference between the B27-posi tive and -negative groups in terms of age (mean +/- SD 38.4 +/- 10 ver sus 39.5 +/- 11 years) and sex ratio (67% versus 68% were men). In add ition, 58 donors (32 B27 positive, 26 B27 negative) agreed to undergo magnetic resonance imaging (MRI) of the sacroiliac joints, A diagnosis of SpA and ankylosing spondylitis (AS) was made according to the Euro pean Spondylarthropathy Study Group criteria and the New York criteria . Results. SpA was diagnosed in 20 persons: 19 of 140 B27-positive (13 .6%) and 1 of 133 B27-negative (0.7%) subjects (15 male and 5 female). AS was diagnosed in 9 persons (7 male and 2 female; 45%), undifferent iated SpA (SpA) in 7 (5 male and 2 female; 35%), psoriatic arthritis ( PsA) in 3 (2 male and 1 female; 15%), and chronic reactive arthritis ( ReA; Reiter's syndrome) in 1 (male; 5%). On that basis of a B27 freque ncy of 9.3% among the population of Berlin (3.47 million persons), the estimated prevalence of SpA was 1.9%, AS was 0.86%, USpA was 0.67%, a nd PsA was 0.29%. The relative risk of developing SpA in B27-positive subjects was calculated as 20.7 (95% confidence interval 4.6-94.2; P = 0.001). Of 58 persons with IBP, sacroiliitis was detected by MRI in 1 5 of 32 B27-positive (46.9%) and 1 of 26 B27-negative (3.9%) subjects (P = 0.002). Four of these 16 donors did not fulfill diagnostic criter ia for SpA. Conclusion. With a calculated prevalence of 1.9%, spondyla rthropathies are among the most frequent rheumatic diseases in the whi te population, HLA-B27 positive persons carry a 20-fold increased risk of developing SpA. AS and USpA are the most frequent SpA subtypes. Pe rsons with IBP who are B27 positive have a 50% likelihood of having sa croiliitis.