Iron in the synovial membrane in rheumatoid arthritis and other joint diseases.

The most constant pathological feature of rheumatoid arthritis is involvement of the synovial membrane. The lesions lack specificity and vary from site to site even in one joint, but generally they show exudation and cell proliferation. The exudates consist of fibrin and inflammatory cells including plasma cells and lymphocytes. Synovial lining cells become larger and more numerous and blood vessel proliferation is prominent. Less commonly reported are giant cells and haemosiderin deposits within the synovial tissue (Sokoloff, 1966). In recent years the fine structure of the normal synovium in man and animals has been described and this has been followed by descriptions of the ultrastructure of rheumatoid synovial tissue. Barland, Novikoff, and Hamerman (1964) have described the presence of large cytoplasmic granules considered to be lysosomes in the Type A lining cell in rheumatoid arthritis. This feature has been confirmed by Hirohata and Kobayashi (1964) and by Norton and Ziff (1966). Recently the presence of ferritin molecules in many of these complex cytoplasmic granules and also scattered throughout the cell cytoplasm in the Type A lining cell has been described (Muirden, 1966). In continuing the latter studies, particles with the molecular dimensions of ferritin have been identified in fourteen out of fifteen open biopsies of synovium from rheumatoid patients. The consistency of this finding on electron microscopy indicated the need to survey larger areas of synovium than is possible with the electron microscope. The purpose of the present study was to examine with the light microscope rheumatoid synovium removed at open operation, using Prussian blue staining to demonstrate the distribution of iron. Samples of both normal synovium and synovium