Synovial metastasis of an adenocarcinoma presenting as a shoulder monoarthritis

A 96-year-old woman presented with monoarthritis of the shoulder from a metastasis affecting both the synovium and the humeral head. Evidence of the metastatic process was based on cytologic study of the synovial fluid (SF), synovial membrane and adjacent bone. A primary cancer site was not discovered. The carcinoembryonic antigen level of SF was greatly enhanced. A similar elevation was not detected in other arthropathies (20 control cases).