A Case of Pseudorheumatoid Nodule Arising in a Previous Site of Squamous Cell Carcinoma.

Abstract

The pseudorheumatoid nodule (PRN) is a subcutaneous palisading granuloma characterized by a pattern of interstitial histiocytes surrounding an area of collagen necrobiosis and typically unassociated with rheumatoid arthritis. It is part of the spectrum of palisading granulomatous dermatitidis which includes the rheumatoid nodule, the rheumatic fever nodule, the spirochaete‐associated juxtarticular nodes of Lyme disease, granuloma annulare, necrobiosis lipoidica and the palisading granuloma of Churg and Strauss. PRN has previously been associated with surgical trauma and with retained suture material at old surgical sites. We present a case of PRN arising in a previous biopsy site of squamous cell carcinoma (SCC). A 48‐year‐old woman with no history of rheumatoid arthritis or a granulomatous diathesis underwent biopsy of a keratotic left forearm skin lesion on 10/14/03 that showed invasive SCC. She had a re‐excision of the the same site on 11/22/03 that grossly showed a central scar. Histology revealed a scar at the site of a recent biopsy with no residual SCC, in the base of which was an area of necrosis palisaded by histiocytes. No residual suture or other polarizable foreign material was identified. Pancytokeratin and Epithelial Membrane Antigen immunostains were negative. The morphology is considered prototypic for PRN.