Intra-articular pseudorheumatoid nodule with an extension block of knee: A rare case report

Subcutaneous nodules characterized by central fibrinoid necrosis, surrounded by histiocytes and fibroblasts, are suggestive of rheumatoid arthritis or rheumatic fever. These nodules, when observed in otherwise healthy individuals, are termed as pseudorheumatoid nodules. These are seen in the scalp, ulnar aspect of the forearm, palm, orbit and dorsum of the foot, with no manifestations of rheumatic disease. These represent an unusual reaction to trauma. Rheumatoid nodules are the extra-articular manifestations of rheumatoid arthritis and it will mimic pseudorheumatoid nodule clinically and on histopathology. Intra-articular pseudorheumatoid nodules, however, are rare. Our case was a 37-year-old female who presented with difficulty in walking and coming down the stairs. The MR evaluation showed a cyst-like lesion in the intercondylar notch of the knee and arthroscopic evaluation and excision determined it to be a rheumatoid nodule. In the absence of any other significant features of rheumatoid arthritis, it is reckoned to be a case of unusual presentation and location of pseudorheumatoid nodule.