E002 Castleman disease presenting with panniculitis and polyarthralgia: lessons from a diagnostic conundrum

Background/Aims A 52-year-old man presented with a 6-month history of bilateral ankle swelling and pain, worse in the mornings and evenings but improving during the day. He also reported migratory erythema ascending his legs, intermittent fevers, and non-specific polyarthralgia. Multiple antibiotic courses for presumed cellulitis were ineffective. This case highlights the diagnostic challenge of Castleman disease, a rare lymphoproliferative disorder that can mimic inflammatory or infectious conditions. Methods Initial investigations revealed persistently raised C-reactive protein with normal HLA-B27, serum urate and ACE levels. MRI of the spine showed no inflammatory spondyloarthropathy. The patient was initially steroid-responsive but later refractory to first-line disease-modifying agents. Dermatology review identified peau d’orange-like skin changes, and biopsy confirmed late-stage panniculitis. PET-CT demonstrated multiple mildly FDG-avid bilateral external iliac and groin lymph nodes, which had increased in size compared with prior imaging. Lymph-node core biopsy confirmed the diagnosis of Castleman disease. Results Castleman disease is under-recognised due to its rarity and variable presentation. It reflects dysregulated immune activation with plasma-cell proliferation within lymphoid tissue. This case underscores the overlap between rheumatological and haematological disease processes and the limitations of standard rheumatology therapies. The patient was transitioned to haematology care and commenced on siltuximab with clinical improvement. Conclusion Castleman disease can mimic rheumatological and infectious conditions, delaying diagnosis. Early recognition and interdisciplinary management are crucial for optimising outcomes. Further research should explore effective disease-modifying strategies for this complex immune-mediated disorder. Disclosure A. Stan: None. R. Winfield: None.