Multiple cutaneous metaplastic synovial cysts

The cutaneous metaplastic synovial cyst is a recently described lesion that characteristically presents as a solitary, tender subcutaneous nodule. On histopathologic examination, the lesion is characterized by a cystic structure with villous-like projections and a lining resembling hyperlastic synovium. The cause of cutaneous metaplastic synovial cysts is unclear, but trauma is presumed to be a precipitating factor, as most reported cases have a history of antecedent cutaneous injury. Here we present a case of multiple, bilateral cutaneous metaplastic synovial cysts in a 72-year-old white man with rheumatoid arthritis. This is the first reported case of a patient with multiple lesions. The characteristic clinical and pathologic features of this lesion, along with proposed cause, are reviewed herein.