OMERACT Definitions

OMERACT (Outcome Measures in Rheumatoid Arthritis Clinical Trials) has a set of consensus definitions for important joint pathologies and an MRI scoring system called the RAMRIS (RA-MRI Scoring).

The definitions and scoring system are focused on the wrist and metacarpophalangeal joints because of their frequent involvement in rheumatoid arthritis and the large amount of MRI data on these joints.

Atlases have been published for the wrist and the metacarpophalangeal joints and should be used for guidance and calibration.

The definitions are as follows:

• Assessed bone volume: Used for scoring bone erosions (see below). In the long bones, the assessed bone volume is from the articular surface (or its best estimated position) to a depth of 1 cm. For the carpal bones, the assessed bone volume is the whole bone.
• MRI bone edema: A lesion, alone or surrounding an erosion or other bone abnormality, within the trabecular bone, with ill-defined margins and fluid signal.
  
  Each bone is scored separately. The scale is from 0–3 based on the proportion of bone with edema. 0: no edema; 1: 1%–33% of bone is edematous; 2: 34%–66% of the bone is edematous; 3: 67%–100% of bone is edematous.
• MRI bone erosion: A sharply marginated bone lesion, with correct juxtaarticular localization and typical signal characteristics, which is visible in 2 planes with a cortical break seen in at least one plane.
  
  Typical signal characteristics on T1-weighted images: loss of normal low signal intensity of cortical bone and loss of normal high signal intensity of trabecular bone. Quick post-gadolinium enhancement suggests presence of active, hypervascularized pannus tissue in the erosion.
  
  Each bone is scored separately. For the wrists: carpal bones, distal radius, distal ulna, and metacarpal bases. For the metacarpophalangeal joints: metacarpal heads and phalangeal bases.
  
  The scale for scoring is from 0–10. The score is based on the proportion of eroded bone compared to the assessed bone volume (see above), judged on all available images. 0: no erosion; 1: 1%–10% of bone eroded; 2: 11%–20%, etc.
• Synovitis: An area in the synovial compartment that shows above normal post-gadolinium enhancement with a thickness greater than the width of the normal synovium.
  
  Synovitis is assessed in three wrist regions (the distal radioulnar joint, the radiocarpal joint, and the intercarpal and carpometacarpal joints) and in each metacarpophalangeal joint. The scale is 0–3 (0: normal, 1: mild, 2: moderate, 3: severe).
  
  The first carpometacarpal joint and the first metacarpophalangeal joint are not scored.

References

• Conaghan P, Bird P, Ejbjerg B, O'Connor P, Peterfy C, McQueen F, Lassere M, Emery P, Shnier R, Edmonds J, Østergaard M. The EULAR-OMERACT rheumatoid arthritis MRI reference image atlas: the metacarpophalangeal joints. Ann Rheum Dis. 2005 Feb;64 Suppl 1:i11-21.
• Ejbjerg B, McQueen F, Lassere M, Haavardsholm E, Conaghan P, O'Connor P, Bird P, Peterfy C, Edmonds J, Szkudlarek M, Genant H, Emery P, Østergaard M. The EULAR-OMERACT rheumatoid arthritis MRI reference image atlas: the wrist joint. Ann Rheum Dis. 2005 Feb;64 Suppl 1:i23-47.
• Østergaard M, Edmonds J, McQueen F, Peterfy C, Lassere M, Ejbjerg B, Bird P, Emery P, Genant H, Conaghan P. An introduction to the EULAR-OMERACT rheumatoid arthritis MRI reference image atlas. Ann Rheum Dis. 2005 Feb;64 Suppl 1:i3-7.