Ultrastructure of the synovial membrane in seronegative inflammatory arthropathies

The ultrastructure of the synovial membrane has been studied in 6 patients with seronegative inflammatory arthropathies: Reiter's (2), Crohn's (2), Whipple's (1) and Behçet's disease (1). The most striking changes were found in the synovial B cells, many containing abnormally large mitochondria with altered cristae surrounded by fibrillar material. Similar material was present in dilated endoplasmic reticulum which was the probable source of groups of extracellular fibrillar spheroidal bodies. The B cells also contained electron dense granular lysosomes of very variable size which, in common with the abnormal mitochondria, were often associated with bundles of orientated microfilaments and large golgi complexes. Light microscopy of the synovial membrane was consistent with an inflammatory arthritis, as were the high white cell counts in the synovial fluid. Systemic activity in the patients was indicated by raised ESR and C-reactive protein (CRP).