Monarthritis: an unusual presentation of renal cell carcinoma.

Two cases of acute monarthritis secondary to asymptomatic renal cell carcinoma are described. This association has not previously been reported. The patients were initially thought to have a septic arthritis, but hot spots were seen on isotope bone scans and biopsy samples showed secondary neoplasms, which were later confirmed to be a result of renal cell carcinomas. The value of cytological examination of synovial fluid when there is clinical doubt as to the cause of a joint effusion is shown.