Tru-cut needle biopsy of subcutaneous fat in the diagnosis of secondary amyloidosis in rheumatoid arthritis.

In order to investigate the presence of secondary amyloidosis in patients with rheumatoid arthritis (RA), we performed an abdominal subcutaneous fat biopsy with a tru-cut needle in 50 patients. The tissue was stained with Congo red and was observed with polarized light microscopy. We found amyloid deposits in 78% of our patients. We randomly selected ten patients with a positive biopsy and a second procedure was performed. Tissues were studied with electron microscopy. We found unbranched fibrils characteristic of amyloid in all of them. We found a direct correlation with rheumatoid factor titers: the more intense the amyloid deposit, the higher the rheumatoid factor titers (p < 0.001). We did not find any correlation between amyloid deposits and clinical manifestations of disease. Amyloid deposits in RA are more frequent than previously thought, and their clinical importance remains to be determined.