Polymyositis in rheumatoid arthritis.

The family of conditions which comprise the polymyositis group have been clarified only in recent years and the syndrome has been extensively reviewed by Walton and Adams (1958), Pearson and Rose (1960), Barwick and Walton (1963), and Pearson (1964). There is now increasing awareness that many cases of polymyositis are to be found in association with diseases of connective tissue. However, the onset of the condition in patients with rheumatoid arthritis, if insidious, may be attributed to simple muscle weakness commonly found in such patients or to a myopathy induced by long-term steroid therapy. If the onset of polymyositis is acute with much systemic upset, the diagnosis may be difficult unless one is familiar with the presenting features of the condition. In order to draw further attention to the association of polymyositis and rheumatoid arthritis, three cases are described below.