More than 150 different diseases are known in which one or more joints may be affected (Huskisson and Dudley Hart 1973). The articular lesions may present the only or the principal symptom, or may be inconspicuous. In many the histopathological picture in the synovium is non-specific, in some typical, rarely it is pathognomonic. The assessment of a synovial biopsy is often made even more difficult by the marked variation between the lesions in different areas within one joint (Cruickshank 1952), and between different joints. Therefore, to many pathologists’ regret a classifying diagnosis can seldom be made with certainty from a synovial biopsy. Often no more than a descriptive diagnosis is possible, which offers insufficient clues to the cause of the lesion.