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A 66-year-old man with chronic olecranon bursitis presented with worsening swelling and pain over the right posterior elbow despite 2 prior treatments with joint aspiration/drainage (which were not submitted for pathological evaluation). Physical examination and imaging revealed prominent soft-tissue swelling over the right olecranon (panel A), and an olecranon bursectomy was performed. Histology showed fibrous bursal tissue infiltrated by anaplastic cells (including hallmark cells) that were CD30⁺, CD2⁺, CD43⁺, multiple myeloma 1/interferon regulatory factor 4 (MUM1)⁺, CD3⁻, CD5⁻, CD4⁻, CD8⁻, T-cell intracellular antigen 1 (TIA1)⁻, CD25⁻, anaplastic lymphoma kinase 1 (ALK1)⁻, CD56⁻, paired box 5 (PAX5)⁻, CD20⁻, CD79a⁻, and CD138⁻ (panels B [H&E, hematoxylin and eosin stain] and C; 60× and 20× objective; original magnification ×600 and ×200, respectively). Fluorescence in situ hybridization analysis revealed IRF4/DUSP22 rearrangement (panel D). Polymerase chain reaction of the T-cell receptor beta gene demonstrated clonal rearrangement. No evidence of systemic or cutaneous disease was detected. No adjuvant therapy was given, and the patient remains disease-free 12 months postsurgery.

This case is one of IRF4/DUSP22-positive anaplastic large cell lymphoma (ALCL) arising in the olecranon bursa. Given the absence of systemic and cutaneous disease (both can demonstrate IRF4/DUSP22 rearrangement), our case represents primary joint or bursal involvement by ALCL, which has not been reported previously to our knowledge. In addition to the clinical history of chronic bursitis and presentation of ALCL in fluid-filled, capsule-enclosed (articular) space (although without evident seroma at time of surgery and no history of joint implant), our case bears similarities to seroma-associated, breast implant–associated ALCL. Similarly, conservative therapeutic approaches (ie, resection followed by clinical monitoring) are appropriate.

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