THU0502 DIFFERENTIAL DIAGNOSIS OF MONOARTHRITIS: THREE CASES WITH PIGMENTED VILLONODULAR SYNOVITIS

Abstract

Background: Pigmented Villonodular Synovitis (PVNS) is a proliferative disorder of synovium that affects synovial joints, tendon sheaths and bursas. The estimated incidence is around 1.8 cases per million people in a population. PVNS is usually found in adults aged 20-50 years, but it may occur also in children. As it is a rare pathology in children, diagnosis is often delayed, and it is difficult to distinguish from Juvenile Idio-pathic Arthritis (JIA), hemophilic arthropathy, tuberculosis, and other neoplastic processes. Objective(s): The aim of this case series is to emphasize PVNS in the differential diagnosis of monoarthritis, and the importance of interpretation of imaging, i.e. MRI. Method(s): Three pediatric PVNS cases who were misdiagnosed as mono-articular JIA and familial Mediterranean fever (FMF) are presented as case series. Result(s): Case-1. A 14 year-old male had swelling and pain on his left knee for one year. An MRI of knee was reported as joint effusion in suprapatellar bursa, and he was referred to our clinic as monoarticular JIA. He was on methotrexate (MTX) 15 mg/m2/wk. SC, and despite effective treatment there was no improvement. MRI was performed by a pediatric radiologist who was an expert on musculoskeletal diseases. Joint effusion and a lesion compatible with PVNS were observed in left supra-patellar recess (Figure-A). Arthroscopic synovectomy was performed and histopathological result was PVNS. Case-2: A one year-old female had swelling on her right knee for three months after a minor trauma. On physical examination, she had effusion of the right knee which was confirmed on USG. She was diagnosed as monoarticular JIA and intraarticular triamcinolone hexacethonide injection was performed. She was unresponsive to adequate non-steroid drug therapy, and MTX was started. Despite intensive therapy, there was no change. MRI showed focal lesions with high signal in T2 weighted images in suprapatellar and intraarticular areas, and findings were evaluated as compatible with PVNS (Figure-B). Total synovectomy was performed and PVNS was confirmed in pathological evaluation (Figure-C). she is in complete remission without treatment. (Figure Presented) Case-3: An eleven-year-old female was referred to our clinic with recurrent swelling and pain on her right knee. Attacks lasted for 2-3 days and resolved spontaneously, accompanied by abdominal pain and vomiting. FMF attack was suspected, for she had signs of peritonitis with knee arthritis, and elevated acute phase reactants. A744S/R202Q compound heterozygote mutations were detected in the MEFV analysis. Col-chicine was started 1 mg/kg/per day. Abdominal pain attacks were resolved with colchicine, but articular symptoms persisted. MRI of the right knee detected focal hyper intense lesions in T2 weighted images compatible with PVNS. Total synovectomy was performed and confirmed PVNS. Conclusion(s): PVNS is a rare but serious reason for joint effusion, presented as chronic arthritis. It should be considered in the differential diagnosis of mono-arthritis, especially when the patient is unresponsive to specific treatment for JIA. MRI is the best diagnostic tool in imaging, and histopathological evaluation should be performed to confirm the diagnosis.