An inflammatory compartment radionuclide such as Indium-111 chloride (111InCl3) may offer advantages over bone seeking radionuclides in the assessment of active rheumatoid synovitis. As an iron analog, 111InCl3 binds iron complexing proteins including transferrin. Active rheumatoid synovitis is a transferrin receptor rich compartment, reflecting profound cellular activation and proliferation. We investigated 111InCl3 scanning for the detection of active rheumatoid arthritis (RA).
Nine patients satisfying ACR criteria for definite or probable RA were scanned twice at a 28-day interval. Patients were undergoing multiple medication changes with resultant fluctuating disease activity. Blinded readings were performed by an experienced nuclear medicine physician and correlated with simultaneous clinical examinations by a single rheumatologist. Sixteen assessed joint areas/patient and a total of 144 joint areas were available for analysis.
Scintigraphy correlated with swollen and tender joint scores at both timepoints. Specificity was highest with stringent scoring. Sensitivity was lowest for small joints with lower 111InCl3 uptake relative to background. A receiver operator curve (ROC), generated to analyze the diagnostic value of varying 111InCl3 scan stringency, demonstrated utilization of the most accurate portion of the ROC curve by the reader.
111InCl3 joint scintigraphy correlates with clinically detectable rheumatoid synovitis, supporting the hypothesis that transferrin receptor levels reflect rheumatoid disease activity.