E028 A differential diagnosis for treatment resistant psoriatic arthritis

Abstract

Abstract Background/Aims This case involves a 45 year old gentleman with established psoriatic arthritis with axial and peripheral joint involvement. His disease was managed with subcutaneous methotrexate and etanercept. Despite improvement in axial symptoms and resolution of symptoms at other peripheral joints, he had ongoing severe monoarthritis of his right knee with significant pain and swelling. Methods In spite of several joint aspirations and intra-articular steroid injections [ten in total], escalation of dose of methotrexate, addition of sulfasalazine and switch of biologic to adalimumab, the patient’s right knee symptoms persisted. Further imaging was performed. An US scan showed chronic synovial hypertrophy with fatty metaplasia and an MRI scan showed frond like synovial thickening, suggestive of lipoma arborescens. Results The patient was referred to the orthopaedic surgeons and underwent excision synovectomy. The histopathology reported fibrofatty tissue with areas of chronic synovitis with presence of lymphoplasmacytic aggregates. The patient’s knee symptoms persisted for five years in total after clinical improvement at other joints; post-synovectomy, his right knee symptoms were improved. Lipoma arborescens is a benign progressive intra-articular lesion characterised by villous lipomatous proliferation of the synovium; it frequently affects the knee joint suprapatellar pouch. Villous proliferation of the synovium occurs, with subsequent replacement of synovial connective tissue by adipocytes. Conclusion Lipoma arborescens has been described occasionally in association with psoriatic arthritis. It is felt to occur as a reactive response to chronic synovial irritation; in this case from an inflammatory affront. Given the rarity of lipoma arborescens, coupled with the patient’s known underlying diagnosis of a seronegative arthritis, there was significant delay in his diagnosis. This case highlights the need to consider other causes of persistent joint pain and swelling when maximal therapeutic options have been unsuccessful. Disclosure A. Jacobs: None. M. Callan: None.