AB1191 DIFFERENTIAL DIAGNOSIS OF SERONEGATIVE ARTHRITIS: DIAGNOSIS ONE YEAR FOLLOW UP AFTER FIRST DIAGNOSIS
Authors: Ichiro Yoshii, Tatsumi Chijiwa, Naoya Sawada
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> The ACR/EULAR classification criteria (AECC) for rheumatoid arthritis (RA) is well known criteria for early diagnosis of RA with high sensitivity. However, the criteria weigh three points for seropositive, thus automatically subtracted 3 points for seronegative arthritis. Recently, elderly onset RA is increasing, that has relatively higher ratio of seronegative than young onset RA. <h3>Objectives</h3> To compare diagnosis of seronegative arthritis between initial and second diagnosis after one year follow up. <h3>Methods</h3> Arthritis patient who are sustained for more than one year since first refer despite his/her ACPA or Rheumatoid Factor were negative, were collected. From these patients, difference from initial diagnosis to second after one year follow up was evaluated statistically with chi square test. Mean EACC score and mean involved joint count for large and small joint (LJC and SJC) at initial diagnosis were compared with each of second diagnosis statistically with Mann Whitney U test (MWU). Clinical course evaluated with 28-joints disease activity score (DAS28) and Health Assessment Questionnaire Disability Index (HAQ-DI) for each diagnosis was compared at every other 3 months with MWU. Comparison between 475 seropositive RA patients treated in the same institute and seronegative RA in the study was also evaluated in a same manner. These patients' sensitivity and specificity (Sens &amp; Specs) in according with 1987 ACR diagnosis criteria (1987ACR) was also evaluated and compared with Sens &amp; Specs of AECC. <h3>Results</h3> Ninety-six patients were enrolled. In these, RA was diagnosed to 18 patients and 78 were unclassified arthritis as first diagnosis. Second diagnosis of these patients were RA for 41, spondyloarthritis (SpA) for 22, other collagen disease (CD) for 5, osteoarthritis (OA) for 9, hypothyroidism (HTh) for 2, non-tuberculotic mycobacterium (NTM) for 1, and unclassified arthritis (UA) for 16. Mean EACC score and range for each second diagnosis was 5.2 and 2 to 7, 4.4 and 3 to 7, 4.4 and 3 to 5, 5.0 and 4 to 6, 4.0 and 4, 4.0, and 4.25 and 3 to 5, for RA, SpA, CD, OA, HTh, NTM, and UA, respectively. There is no significant difference between any pair of second diagnoses. LJC and SJC of each second diagnosis was 3.2 and 9.8, 5.7 and 4.8, 2.4 and 4.8, 2.4 and 8.1, 2.0 and 6, 2 and 2, and 1.8 and 5.9, for RA, SpA, CD, OA, HTh, NTM, and UA, respectively. There is also no significant difference between any pair of second diagnoses (Table). In clinical course, there is no significant difference between the second diagnoses, and also no significant difference between seropositive and seronegative RA. In these seronegative arthritis patients, Sens &amp; Specs of RA in accordance with 1987ACR were 75.0% and 43.4%, while 83.3% and 66.7% in accordance with AECC. <h3>Conclusion</h3> Diagnosis of seronegative RA is not uncomplicated, whereas rheumatologist's diagnostic skill is questioned. <h3>Disclosure of Interests</h3> None declared