Effect of intravenous iron dextran on rheumatoid synovitis.
Eleven patients with rheumatoid arthritis received a total dose infusion of iron dextran for anaemia. Two of them had anaphylactic reactions and the remaining nine an exacerbation of synovitis. Quantitative infrared thermal imaging was used to assess the extent and distribution of joint involvement resulting from this therapy. In all eight patients examined the 'thermographic index' increased in two or more joint areas, indicating an increase in inflammation. Small joints of the hands were maximally affected, though larger joints when previously inflamed also worsened. Uninflamed joints were rarely affected. The exacerbation of synovitis occurred 24-48 h after completion of the iron dextran infusion and corresponded with a saturating of the serum iron binding capacity. Levels of immune complexes were unaltered, implying normal reticuloendothelial function. In one further patient, reported to have synovial flares when challenged with oral ferrous sulphate, iron dextran was infused at a lower dosage. All previously inflamed joints in this patient worsened 12 h after the infusion was discontinued. Concomitant with this was an increase of lipid peroxidation products in synovial fluid and to a less extent serum. Iron dextran in vitro stimulated lipid peroxidation, but dextran alone had no effect. It is therefore suggested that iron dextran worsens synovial inflammation by promoting lipid peroxidation.