MAGNETIC RESONANCE IMAGING IS SENSITIVE FOR THE DETECTION OF RHEUMATOID ARTHRITIS JOINT PATHOLOGIES, BUT LACKS SPECIFICITY

2. [2008] [OP-0184] MAGNETIC RESONANCE IMAGING IS SENSITIVE FOR THE DETECTION OF RHEUMATOID ARTHRITIS JOINT PATHOLOGIES, BUT LACKS SPECIFICITY

E. Olech1, J.V. Crues², D.E. Yocum³, P. Kamp1, J.T. Merrill^{1 1}Pharmacology, Oklahoma Medical Research Foundation, Oklahoma City; ²Radnet Management, Los Angeles; ³Immunology, Tissue Growth and Repair, Genentech, Inc., San Francisco, United States

Background: Specificity of Magnetic Resonance Imaging (MRI) for the detection of Rheumatoid Arthritis (RA) joint pathologies has not been well established. There are only a few published studies assessing bony lesions or synovitis-like changes in healthy subjects. In addition, the subject numbers in prior studies were small and the readers evaluating images were usually not blinded to the subjects' diagnosis.

Objectives: In order to calculate the sensitivities and specificities of MRI-detected erosions, bone edema and synovitis in the metacarpophalangeal and wrist joints in RA, images of 40 healthy subjects (employees of the Oklahoma Medical Research Foundation) and 40 RA patients from the Oklahoma RA Cohort were evaluated.

Methods: The study had institutional review board approval. MRI of the bilateral hand and wrist was performed using a 0.2 T dedicated-extremity MRI unit (C-scan). Coronal T1-weighted 3-dimensional gradient echo with thin slices (0.6 – 0.9 mm) and coronal fat-suppressed short tau inversion recovery (STIR) sequences were obtained. The images were evaluated for bone erosions, bone marrow edema and synovitis by a trained, blinded observer using the OMERACT MRI scoring system (RAMRIS). In order to determine the inter-reader reliability for MRI scores, images of 10 subjects were also read independently by a musculoskeletal radiologist. Agreement between the two observers was determined by intra-class correlation coefficient (ICC).

Results: F/M ratio and mean age of the healthy controls were 29/11 & 36.7, RA subjects: 32/8 & 47.3 respectively. Mean RA duration was 83.5 months, median: 47. 72.5% of RA patients were RF+; 58% were anti-CCP+ and 50% were both RF and anti-CCP positive. One healthy volunteer was anti-CCP positive. Mean ESR & CRP was 11 & 0.48 in controls and 29 & 1.32 in RA respectively.

The ICC between the two readers was 0.76 for individual joints and 0.88 for total scores.

A total of 3360 (1680 in each group) bones were evaluated. 514 erosions were found; 62% of them were in the wrist bones. Both groups had the highest number of erosions and erosion scores in the 3rd metacarpal head. The highest scores for bone edema were found in the lunate and for synovitis in the intercarpal joint area in both groups.

Twenty six healthy subjects (65%) had at least one erosion, 7 (17.5%) had bone edema, and 17 (42.5%) had changes resembling synovitis. Four (10%) RA patients were erosion free.

If having one erosion on MRI of bilateral hand and wrist was a positive test for RA, the sensitivity of this test would be 90%, but specificity only 35%. Presence of bone edema appears to be a better test for RA with 82.5% specificity and 60% sensitivity. Having an erosion in the dominant wrist has 70% sensitivity and 65% specificity for RA. Having > 5 erosions or erosion score > 8 in both hands and wrists is 90% specific for RA with sensitivity of 55% and 57.5% respectively.

Conclusion: While MRI is highly sensitive for identifying bone erosions, it does not provide good specificity for RA. The presence of bone edema is more specific for RA and provides fair sensitivity.

Ann Rheum Dis 2008;67(Suppl II):106