A Case of Sporadic Blau Syndrome with an Uncommon Clinical Course.

Background: Sporadic Blau syndrome (SBS), a rare systemic inflammatory disease in children, is associated with NOD2 gene mutations. SBS is often misdiagnosed as juvenile idiopathic arthritis (JIA) because of their similar clinical manifestations. Herein, we present a case of SBS with an uncommon clinical course.

Case Presentation: An 11-year-old girl with recurrent right ankle swelling for 4 years was referred to our hospital. One month before admission, she developed an intermittent high fever. She was diagnosed with systemic-onset JIA on the basis of physical and blood examination results. She was treated with ibuprofen, prednisolone, and methotrexate for 5 years. During this period, her joint lesion showed neither bone destruction nor joint space narrowing on radiography, which are characteristics of JIA. Twelve months after the termination of methotrexate treatment, she presented with bilateral panuveitis. A missense mutation, p.(R587C), was detected in her NOD2 gene, and she was diagnosed with SBS. Then, infliximab treatment was started, and her visual acuity recovered.

Conclusion: SBS may sometimes be misdiagnosed as JIA. A joint lesion without bone destruction might be a key feature to distinguish SBS from JIA. Analysis of the NOD2 gene is recommended in such cases.