SAT0358 EROSION MIGHT INCREASE PROBABILITY OF POSITIVE AXIAL SPONDYLOARTHRITIS (SPA) DIAGNOSIS IN PATIENTS WITH EARLY INFLAMMATORY BACK PAIN(IBP). A PROSPECTIVE 3.5 YEAR FOLLOW UP OF 133 PATIENTS
Authors: Liliya Yankova Komsalova, Pilar Martinez, Jose Fermin Gomez, Antonio Valdivia
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Objectives</h3> To analyse sensitivity, specificity and predictive values of inflammatory back pain (IBP), positive HLA B27 antigen, increased C-reactive protein (CRP), clinical features (CF) such as peripheral arthritis, dactylitis, psoriasis, uveitis, inflammatory bowel disease and enthesitis, familial history (FH) of SPA and assess probabilities to develop SPA. To evaluate the impact of chronic (T1) MRI lesions in early diagnosis of SPA <h3>Methods</h3> We prospectively collected and followed up 133 patients referred to our department with suspicion of SPA from September 2014 to March 2018. Data such as IBP, HLA B27 antigen, increased CRP, CF, FH and sacroiliac X-rays were collected for each patient. STIR and T1 MRI imaging were separately and independently evaluated by a rheumatologist and two radiologists. In case of disagreement, agreement between two readers was regarded as conclusive. MRI STIR sacroiliac joints (SI) images were assessed in a semi-qualitative way as follows: 1) strongly positive MRI imaging(SPMRI): patients with at least 2 highly specific bone marrow oedema(BME) lesions, easily classifiable as SPA. 2) Weakly positive MRI imaging(WPMRI): patients with at least 2 tiny BME lesions, suggestive, but not easily classifiable as SPA. 3) Clearly negative MRI imaging: patients without any of those features. T1 SI MRI images were assessed for erosion, fat metaplasia, backfill and sclerosis in a qualitative way as positive, if there were 1 or more than one, or negative, if there were none of those lesions. <h3>Results</h3> The average age in our study was 38.9 years. 47(35.3%) patients received diagnosis axial SPA. Radiographic sacroiliitis had 8(17%). Sensitivity (St), specificity (Sf) and predictive positive values (PPV) were found as follows for each item (p&lt;0.001): IBP: 83% St, 81.4% Sf, 71%PPV, positive HLA B27: 49% St, 80% Sf, 57.5% PPV, increased CRP: 40.4% St, 93% Sf, 76% PPV, and CF: 36.2% St, 91% Sf, 68%PPV. Multivariate logistic regression binary analysis applied to the group of patients with non-radiographic SPA showed Odds Ratios for positive diagnosis, 64.8 for IBP (p=0.000), 9.4 for increased CRP (p=0.005) and 11.9 for CF (p=0.006). For the total group of patients the Odds Ratios were as follows: 49.2 for IBP (p=0.000), 10.3 for increased CRP (p=0.002) and 11.3 for CF (p=0.002). STIR MRI imaging assessment proved acceptable sensitivity (79%), excellent specificity (94%), and high PPV (88%) for SPMRI (p&lt;0.001). WPMRI displayed better sensitivity (87%) nonetheless, specificity (67%) and PPV decreased (59%) (p&lt;0.001). T1 MRI examination showed reasonable sensitivity (72%) excellent specificity (97%) and high PPV (85%) for erosion (p&lt;0.001). Sensitivity for backfill was lower (32%), but specificity (100%) and PPV (100%) were excellent (p&lt;0.001). Association, erosion and SPMRI pointed out a highly strong specificity (100%) and PPV (100%), however decreased sensitivity (51%) (p&lt;0.001). Association, erosion and WPMRI significantly increased specificity (98%) and PPV (94%), although slightly decreased sensibility (64%)(p&lt;0.001). Inter-observer agreement was higher for STIR MRI performance 0.70(95%CI0.59; 0.80), and lower for T1 0.47 (95% CI 0.35; 0.59). <h3>Conclusion</h3> At the onset, IBP, increased CRP, CF and IBD might be good indicators for selecting patients with a higher likelihood of positive diagnosis. Strongly positive SI MRI imaging is highly specific, brings acceptable sensibility and may be an excellent tool for early diagnosis of SPA. Weakly positive MRI STIR imaging might be helpful to detect patients with early SPA but lacks specificity. Early detection of erosion adds additional value to the STIR MRI reading, enhancing the specificity and increasing the probability of positive SPA diagnosis <h3>Disclosure of Interests</h3> None declared