Development and preliminary validation of a magnetic resonance imaging joint space narrowing score for use in rheumatoid arthritis: potential adjunct to the OMERACT RA MRI scoring system.

OBJECTIVE

To develop and validate a magnetic resonance imaging (MRI) method of assessment of joint space narrowing (JSN) in rheumatoid arthritis (RA).

METHODS

Phase A: JSN was scored 0-4 on MR images of 5 RA patients and 3 controls at 15 wrist sites and 2nd-5th metacarpophalangeal (MCP) joints by 8 readers (7 once, one twice), using a preliminary scoring system. Phase B: Image review, discussion, and consensus on JSN definition, and revised scoring system. Phase C: MR images of 15 RA patients and 4 controls were scored using revised system by 5 readers (4 once, one twice), and results compared with radiographs [Sharp-van der Heijde (SvdH) method].

RESULTS

Phase A: Intraobserver agreement: intraclass correlation coefficient (ICC) = 0.99; smallest detectable difference (SDD, for mean of readings) = 2.8 JSN units (4.9% of observed maximal score). Interobserver agreement: ICC = 0.93; SDD = 6.4 JSN units (9.9%). Phase B: Agreement was reached on JSN definition (reduced joint space width compared to normal, as assessed in a slice perpendicular to the joint surface), and revised scoring system (0-4 at 17 wrist sites and 2nd-5th MCP; 0: none; 1: 1-33%; 2: 34-66%; 3: 67-99%; 4: ankylosis). Phase C: Intraobserver agreement: ICC = 0.90; SDD = 6.8 JSN units (11.0%). Interobserver agreement: ICC = 0.92 and SDD = 6.2 JSN units (8.7%). The correlation (ICC) with the SvdH radiographic JSN score of the wrist/hand was 0.77. Simplified approaches evaluating fewer joint spaces demonstrated similar reliability and correlation with radiographic scores.

CONCLUSION

An MRI scoring system of JSN in RA wrist and MCP joints was developed and showed construct validity and good intra- and interreader agreements. The system may, after further validation in longitudinal data sets, be useful as an outcome measure in RA.