S-43 Department of Rheumatology VU University Medical Centre, Amsterdam, The Netherlands. Irene E. van der Horst-Bruinsma, MD, PhD Willem F. Lems, Prof. Dr, MD Ben A.C. Dijkmans, Prof. Dr, MD Please address correspondence to: I.E. van der Horst-Bruinsma, MD, PhD VU University Medical Centre, Department of Rheumatology, room 3A-64, P.O. Box 7057, 1007 MB Amsterdam, The Netherlands. E-mail: IE.vanderHorst@vumc.nl Received and accepted on July 29, 2009. Clin Exp Rheumatol 2009; 27 (Suppl. 55): S43-S49. © Copyright CLINICAL AND EXPERIMENTAL RHEUMATOLOGY 2009. Key words: Rheumatoid arthritis, ankylosing spondylitis, clinical symptoms. Competing interests: none declared. ABSTRACT The clinical manifestations of rheu- matoid arthritis (RA) and ankylosing spondylitis (AS) differ in many ways. The age of onset in AS is much younger, with an average onset of 28 years com- pared with 40–50 years in RA, and with a male predominance (3:1) compared with the female predominance in RA. The genetic assocition with HLA alleles is stronger in AS, with an HLA-B27 an- tigen in 95% of the patients compared with RA, with 60% HLA DR4 or DR 1 positives. The type and localisation of arthritis is peripheral polyarthritis in RA, especially with involvement of hands and feet, whereas in AS the ar- thritis is mainly localized in the spine and sacroiliac joints with an oligoar- thritis of the larger joints (hips, knees, shoulders). The radiographic signs in RA show bone resorption with erosive changes in contrast with AS where bone formation with vertebral sydesmophytes is present. Extra-articular manifesta- tions can occur in both diseases but again these manifestations differ in the eye (keratoconjuctivitis sicca and scle- ritis in RA, versus anterior uveitis in AS), heart (pericarditis in RA, conduc- tion disturbances in AS), lungs (pleural lesions or nodules in RA and fibrosis in AS) and gastrointestinal tract (peptic ulcers in RA and colitis in AS). Both diseases respond well to treatment with NSAIDs but DMARDs, which are very important in RA, have limited value in AS. TNF alfa blocking drugs, however, show a high efficacy in both diseases. Definition of the diseases Rheumatoid arthritis has a prevalence of 1–2% in the Caucasian population (Table I) and is characterised by poly- arthritis, especially of the small joints of hands and feet. The diagnosis is made on clinical judge- ment of the rheumatologists. The most often used classification criteria are the 1987 American Rheumatism Associa- tion (ACR criteria) (1) which include symmetrical polyarthritis, involvement of the hand joints, rheumatoid nodules, radiographic erosions and the presence of the rheumatoid factor. Unfortunately the ACR-criteria lack sensitivity early in the disease (2). Ankylosing spondylitis (AS) has a prevalence up to 0.9% in the Caucasian population (3) (Table I) and presents with low back pain and morning stiff- ness due to a chronic inflammation of the sacroiliac (SI) joints and vertebral column. The diagnosis of definite AS requires fulfilment of the modified New York criteria (4): obligatory are signs of a bilateral sacroiliitis grade 2-4 or unilateral sacroiliitis grade 3 or 4 at the x-ray of the pelvis (Fig. 3) plus at least one criterion out of 3 (inflammatory back pain, limited lumbar spinal mo- tion in sagittal and frontal planes and decreased chest expansion relative to normal). Etiology RA as well as AS have a multifacto- rial cause, but genetic influences play a major role in both diseases. In RA, specific Human Leukocyte Antigen (HLA) class II genes at HLA-DR4 (DRB1*0404 and 0401) and DR1 (DRB1*1001), are present in 60% of the patients. In AS, the main genetic component is localized at an HLA class I gene, HLA-B27 (5), which is present in 95% of the patients (Table I). The age at onset differs between RA and AS, because the first symptoms of AS most often starts at an earlier age com- pared with RA. RA can start at any age, but there is a peak incidence between 40-70 years of age. In contrast, AS most often begins in late adolescence or early adulthood with an average age of onset at 28 years (6). The onset of complaints in AS is often gradual and A systematic comparison of rheumatoid arthritris and ankylosing spondylitis I.E. van der Horst-Bruinsma, W.F. Lems, B.A.C. Dijkmans