BACKGROUND AND AIM: Rheumatoid arthritis (RA) is a chronic polyarthritic syndrome in which actively inflamed joints coexist with others being in remission. Compatible bone scan (BS) reveals joints with increased activity due to degenerative alterations, whilst scanning with human polyclonal immunoglobulin (HIG) is capable to show which of the joints present active inflammation of the synovial membrane. The aim of the study is to investigate the utility of molecular imaging with HIG in patients suffering from RA.PATIENTS AND METHODS: Forty patients (9 males plus 31 females), suffering from painful polyarthritic syndrome, with a mean age 45.3±7 years and a duration of disease 18.3±4.2 months were enrolled in the study. Twenty-six of the patients were serum positive to RA factor, considered as suffering from RA, whilst fourteen of them were RA factor negatives and they were considered as patients with serum-negative polyarthritis. All patients were submitted to x-rays and ultrasound examination (US) in joints of interest, plus whole body BS with (99m)Tc-MDP and finally scan with (99m)Tc-HIG.RESULTS: A total of 1680 joints have been evaluated. In 6 of the patients-two with serum negative RA (252 joints), radionuclide imaging with HIG was within normal limits, despite the fact that in compatible bone scan degenerative alterations have been mentioned in 30 joints. In all these patients disease was evaluated as inactive ("arthrotic changes"). In the remaining 34 patients-12 with serum negative RA (1428 joints), increased accumulation of HIG, concerning serum positive patients, has been mentioned to 163 joints ("arthritic changes"), whilst in the same group, BS revealed degenerative changes to 265 joints. Concerning serum negative patients, the respective results were 64 versus 190 joints. Increased uptake of HIG has been found in 189/226 swollen and painful joints (overall sensitivity according to clinical criteria 83.3%) and in 38 joints without any clinical evidence of inflammation, with clinical active inflammation presented after follow-up to 35 of them, yielding thus specificity at the level of 92%. Matched findings between these two methods have been mentioned to 185 out of 227 joints with an abnormal scan with HIG. Abnormal x-rays and US findings have been mentioned in 67 of the joints.CONCLUSIONS: According to the above mentioned, BS in RA reveals joints being actively inflamed or not, whilst radionuclide study with HIG is capable to distinguish actively inflamed joints, even in patients with serum negative RA, in a greater extent than anatomical imaging modalities.