Case Presentation
A 12-year-old Japanese girl presented with normal birth and developmental history. There was no notable family or medical past history. At 2 years old, she experienced swelling of both knee joints without any cause. There was no rest pain in either knee; however, pain on motion in the right knee and joint effusion in both knees were noted at the first examination. Full extension was observed for the right knee but flexion was limited to 130°. The left knee had a normal range of movement. Aspiration of clear yellow joint fluid showed a negative culture result. Laboratory findings showed a white blood cell (WBC) count of 10,700/μL, C-reactive protein (CRP) of 0.45mg/dL, and erythrocyte sedimentation reaction (ESR) of 21mm/hour. Magnetic resonance imaging (MRI) revealed small masses in her knee joints (Figure 1). Her symptoms were not improved after several joint aspirations. Arthroscopic synovectomy was eventually performed for both knees. During the operation, rice bodies and thickening of the synovial membrane were observed (Figure 2). The pathological findings for the rice bodies showed acidophilic tissues with lymphoid infiltration (Figure 3); however, no definite diagnosis was made. After the operation, the pain and swelling in the knees were improved. A 10-year asymptomatic period after arthroscopic synovectomy precluded the need for annual medical examinations.
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Figure 1.
Magnetic resonance imaging (T2-weighted) at 2 years showed a small mass in her knee joint (arrows).
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Figure 2.
Arthroscopic findings at 2 years showed rice bodies and thickening of the synovial membrane. Removal of the rice bodies and synovectomy was performed for both knees.
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Figure 3.
Pathological findings of the rice bodies revealed acidophilic tissues with lymphoid infiltration.
When she was 12 years old, her left knee again showed swelling without any cause. Several joint aspirations and intra-articular injection of steroids failed to improve her symptoms. She did not experience any pain in her left knee. Full extension was observed for her knee but flexion was limited to 130°. Laboratory findings revealed a WBC count of 4,300/μL, CRP of 0.10mg/dL, ESR of 12mm/hour, rheumatoid factor (RF) of < 5IU/mL, matrix metalloproteinase-3 of 95.1ng/mL, and an antinuclear antibody (ANA) test was 1:80 positive. Contrast-enhanced MRI showed joint effusion and thickening of the synovial membrane (Figure 4). An arthroscopic synovectomy was performed for her left knee (Figure 5), and pathological findings revealed the presence of a villiform structure, increased blood vessels, chronic inflammatory cells, and lymphocyte infiltration (Figure 6). She had no uveitis, but was diagnosed with JIA and received methotrexate (MTX) medication. Since that time there has been no recurrent knee arthritis.
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Figure 4.
Contrast-enhanced magnetic resonance imaging (fat suppression T1-weighted) at 12 years showed joint effusion and thickening of the synovial membrane.
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Figure 5.
Arthroscopic findings during synovectomy at 12 years. A: Anterior cruciate ligament and the engorged synovial membranes. B: The synovial membranes in the suprapatellar pouch.
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Figure 6.
Pathological findings at 12 years revealed the presence of a villiform structure, increased blood vessels, chronic inflammatory cells, and lymphocyte infiltration.