Clinical and pathologic studies of synovitis in polymyalgia rheumatica.

Clinically detectable joint swelling was found in 10 of 13 fully evaluated patients considered to have polymyalgia rheumatica. Five patients had some joint findings at disease onset. Knees were most commonly affected. Sternoclavicular involvement was seen in 3 patients. Joint effusions in 8 patients had 300-5,700 leukocytes/mm3 with a mean of 2,900. Six synovial biopsy specimens studied by light microscopy revealed mild to moderate synovial proliferation and chronic inflammation that was generally less severe than in typical rheumatoid arthritis. Electron microscopy identified microvascular changes and large amounts of vesicular and granular debris in lining cells. In 1 patient, a "fingerprint" pattern in the granular material was suggestive of the findings in some immune complexes. This still unexplained synovitis may, as previously suggested, be important in the pathogenesis of the polymyalgia rheumatica syndrome.