Pulmonary squamous cell carcinoma metastatic to the proximal interphalangeal joint of the right finger: report of a rare case and review of the literature.

Synovial metastasis is a rare condition with only a few cases reported in the literature. Synovial metastasis to the finger or toe joint is different from acrometastasis, which is defined as bone metastasis located distal to the elbow and knee. The most common site of synovial metastasis is the knee joint. Conversely, synovial metastasis to the finger or toe joints has, to our knowledge, been reported in one case only so far. Herein, we report the second case of synovial metastasis to the proximal interphalangeal joint of the right third finger in a patient with metastatic pulmonary squamous cell carcinoma and review the literature on synovial metastasis.