Isolated intra-articular pseudorheumatoid nodule of the knee

The authors describe a case of an isolated intra-articular pseudorheumatoid nodule of the knee in an 18-year-old male patient without a diagnosis of rheumatoid arthritis. The patient initially presented with a 3 year history of anterior knee pain and was found to have a 2.8 × 2.1 cm lobulated soft-tissue mass. Histologic findings showed fibrinoid necrosis and chronic inflammatory changes that were consistent with those of a pseudorheumatoid or rheumatoid nodule, and surgical excision of the nodule was curative. A review of the literature revealed no prior cases of an intra-articular pseudorheumatoid nodule or rheumatoid nodule in a patient without clinical or serologic evidence of rheumatoid arthritis.