Abstract
Background We present a case of juxta-articular pseudorheumatoid nodules from atypical granuloma annulare as a mimic for true rheumatoid nodules.
Case Report An 86-year-old male was sent to our rheumatology clinic for evaluation of rheumatoid arthritis. His past medical history was relevant for localized squamous cell carcinoma of the penis, chronic kidney disease, type 2 diabetes mellitus, COPD, provoked pulmonary embolism, and peripheral arterial disease. He was initially sent to a plastic surgeon for multiple painless, skin-colored nodules on his hands and forearms. He had 2 nodules excised and sent for pathology. On both occasions, palisaded granulomatous inflammation with histiocytes and necrobiosis was seen, consistent with rheumatoid nodules (Figure 1A,B). However, on clinical assessment there was no suggestion of previous or current inflammatory arthritis on history or physical exam. There was no history of methotrexate use suggesting methotrexate nodulosis. CT scan of the chest, abdomen and pelvis was negative for active malignancies. Infectious disease consultation did not reveal any other infectious causes, including syphillis. Rheumatoid factor, anti-cyclic citrullinated peptide antibodies (ACPA) and anti-nuclear antibody (ANA) testing were negative. Acid-Fast Bacilli, Grocott Methenamine Silver, Periodic Acid Schiff special stains on the excised nodules were negative for mycobacterial and fungal organisms. Alcian Blue stain was also not prominent (Figure 1C). Given the inconsistency between the clinical context and histologic findings, this case was re-reviewed by 2 dermatopathologists. It was determined that the most likely diagnosis was a rare, variant of nodular granuloma annulare known as a “juxta-articular pseudorheumatoid nodule”, which can have identical or near identical histology to a rheumatoid nodule. The patient is now followed by dermatology, with a plan of observation and surgical excision as needed.
Histological Findings of Excised Nodules
Conclusion Rheumatologists, dermatologists, and pathologists should be aware of this rare entity, to avoid confusion and misdiagnosis of rheumatoid arthritis. This phenomenon is uncommon in adults; documentation is limited to case series and its etiology and natural history in adults are not well documented.[1-3] Distinction on histology from a rheumatoid nodule cannot be made with certainty, but it is possible that pseudorheumatoid nodules can have more histiocytes, mucin, and less stromal fibrosis.[1] Ultimately clinical correlation is important to distinguish from rheumatoid nodules.[1-3] Surgical excision is the most common treatment, although many non-surgical options have been described with limited efficacy and evidence.[2,3]
References [1.] Barzilai A. Am J Dermatopathol 2005;27:1-5. [2.] Bizimungu S. JAAD Case Rep 2025;63:8-10. [3.] Sturm B. Dermatol Online J 2020;26:5.
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