Background Remission of disease is the best possible outcome of treatment regimens in rheumatoid arthritis (RA). However, definitions of clinical remission, including the most recent ACR/EULAR definitions are all based on clinical signs, laboratory values and patient (and physician) reported measures and may not rule out residual disease activity. Such disease activity may have prognostic relevance since progressive joint damage occurs in 15% of RA patients in remission. Residual synovitis may be well detected by macrophage targeting ((R)-11C-PK11195) and positron emission tomography (PET). This technique has previously been successful in the detection of (subclinical) synovitis in preclinical (ACPA+ arthralgia) RA patients and established RA patients.
Objectives Pilot study to determine whether macrophage targeting by (R)-11C-PK11195 PET can visualise subclinical joint inflammation in RA patients without signs of clinical synovitis, with a flare of arthritis as outcome measure and MRI as reference imaging technique.
Methods (R)-11C-PK11195 PET and contrast-enhanced MRI of hands/wrists were performed in 29 RA patients without clinical synovitis. (R)-11C-PK11195 uptake (visual score: 0 (low)-3 (high)) in metacarpophalangeal, proximal interphalangeal and wrist joints (n=22 joints/patient) was scored and corrected for background uptake. Individual joint scores were summed to obtain a cumulative PET score (range 0-66). MRI RAMRIS scoring was performed of the same hand joints as were evaluated by PET. Synovitis and bone edema scores (>1) were summed to obtain a cumulative MRI score (range 0-288). Flare of arthritis during a 3-year follow up was determined by screening patients’ medical records.
Results Clinical flare of arthritis was reported in 17/29 (59%) of patients within three years. (R)-11C-PK11195 PET showed enhanced tracer uptake in at least one hand and/or wrist joint in 16/29 (55%) of patients, of which 69% developed a flare of arthritis during the follow-up period. Cumulative PET scores of patients developing a flare of arthritis were higher than that of patients without a flare (median (IQR) = 2 (0-4.5) vs 0 (0-1), p=0.03). Maximum cumulative PET and MRI scores were respectively 24 and 40. Highest cumulative PET scores (>6, n=3) corresponded with highest cumulative MRI scores (>39) and were associated with development of a flare of arthritis in hands/wrists within 26 weeks. All patients that did not develop a flare of arthritis had low cumulative PET scores (≤1), while cumulative MRI scores of these patients varied much more and were not significantly lower than that of patients with a flare.
Conclusions (R)-11C-PK11195 PET showed enhanced uptake, pointing to presence of subclinical synovitis, in over half of the patients without clinical synovitis. At patient level, high cumulative PET scores (comparable to high scores on MRI) may predict flare of arthritis. In particular with regard to specificity, PET may add diagnostic value to detection of subclinical synovitis in these patients.
Disclosure of Interest None Declared