Low synovial clearance of iodide provides evidence of hypoperfusion in chronic rheumatoid synovitis

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Abstract
Iodide clearance was measured in the chronic knee effusions of 11 patients with rheumatoid arthritis and 9 patients with osteoarthritis. The mean (±SE) iodide clearance of 1.92 ± 0.30 ml/minute in rheumatoid arthritis effusions did not differ significantly from the 2.19 ± 0.52 ml/minute found in osteoarthritis effusions. Clearance values in rheumatoid arthritis patients ranged widely (0.79–3.22 ml/minute). Iodide clearance in these patients correlated directly with synovial fluid (SF) pH (r = 0.731, P = 0.005), SF glucose: serum glucose ratio (r = 0.746, P = 0.004), and SF temperature (r = 0.878, P = 0.001), and indirectly with SF lactate (r = −0.782, P = 0.002) and percentage of SF neutrophils (r = −0.581, P = 0.03). These relationships support the hypothesis that rheumatoid synovitis is often marked by tissue hypoperfusion, and that the “sickest” rheumatoid joints (as defined by physiologic indices) are the most ischemic.