Chronic Arthritis of the Knee due to Synovial Metastasis

「ABSTRACT」A 65-year-old man with advanced gastric adenocarcinoma complained of left knee pain and swelling lasting for 2 months. Laboratory studies demonstrated mild inflammation and hemorrhagic joint effusion. Magnetic resonance imaging revealed hydrarthrosis and a tumor within the suprapatellar pouch. Diagnostic arthroscopy with multiple synovial biopsies indicated metastatic adenocarcinoma. Synovial metastasis is rare. To the best of our knowledge, this is the first case of synovial metastasis of adenocarcinoma to be reported in Japan, and only 47 cases have been reported worldwide. The diagnosis can be established with cytologic examination of the synovial fluid or histopathologic examination of the synovium. The knee is the most frequently affected joint, and adenocarcinoma is the main histopathological type. The mechanism of synovial metastasis remains unclear. In the present case, spread via a hematogenous route was considered most likely. Because disease metastatic to a joint carries a poor prognosis, with an average survival of less than 5 months, the possibility of joint metastasis should be considered in an elderly patient with a malignancy and chronic arthritis. Early cytological or pathological examinations are important because they allow better treatment and care.