Utility of Tc-99m Human Polyclonal Immunoglobulin G Scintigraphy for Assessing the Efficacy of Yttrium-90 Silicate Therapy in Rheumatoid Knee Synovitis

PURPOSE The aim of this study was to determine the utility of Tc-99m human polyclonal immunoglobulin G (HIG) scintigraphy for evaluating the efficacy of yttrium-90 (Y-90) silicate therapy in rheumatoid knee synovitis. MATERIALS AND METHODS Fifteen patients (13 women, 2 men; mean age, 53.5 ± 8.4 years) with rheumatoid arthritis had radionuclide synovectomy using 185 MBq (5 mCi) Y-90 silicate to evaluate 24 knee joints with chronic persistent synovitis. Radiologic and clinical evaluations and Tc-99m HIG scans were performed in each patient before radionuclide synovectomy. Each patient was reassessed 3, 6, 9, and 12 months after therapy using clinical examination and Tc-99m HIG scintigraphy. RESULTS In 14 of 24 knee joints (4 Larsen stage I, 10 Larsen stage II) that had excellent or good clinical responses to Y-90 silicate therapy, the Tc-99m HIG index values 3 months after treatment were significantly lower than the pretreatment index values (P < 0.001). In 13 of these 14 joints, these low index values and clinical results remained constant throughout the 1 year of follow-up. One patient (1 of the 14 knee joints) experienced severe pain and swelling as a result of recurrent arthritis at 9 months, and the Tc-99m HIG index value increased at 9 months and remained high 12 months after therapy. In 10 of 24 knee joints (4 Larsen stage II, 6 Larsen stage III) that had a fair or poor clinical response, Tc-99m HIG index values were statistically similar before and after radionuclide therapy. CONCLUSIONS Quantitative Tc-99m HIG scintigraphy is a valuable method for assessing the efficacy of Y-90 silicate therapy in rheumatoid knee synovitis.