Background/Purpose:

Systemic-onset juvenile idiopathic arthritis (s-JIA) is a systemic inflammatory disorder manifesting spiking fever, rheumatoid rash, and arthritis. The onset is nonspecific, and may be triggered by infectious agents. A body of evidence indicates involvement of cells and inflammatory cytokines produced in innate immune response in the induction phase of the disease, and then augmented in an auto-inflammatory fashion, suggesting that s-JIA may be one of the auto-inflammatory diseases. However, the causative agents and the responsible organs for exaggerated innate immune responses are still to be elucidated. The ¹⁸F-FDG-Positron Emission Tomography (PET) is a hybrid imaging technique displaying the sites of high metabolic turnover of both physiologic and pathologic origin and visualizes infection focus and inflammatory lesions as well as malignancy. Application of ¹⁸F-FDG-PET to patients with s-JIA will possibly localize inflammatory lesions of this disease.

To examine and delineate inflammatory focus in patients with s-JIA, ¹⁸F-FDG-PET was applied to patients with s-JIA and polyarticular (p)-JIA, and the images of these patients were compared.

Methods:

  Sixty eight children (57 with s-JIA and 11 with p-JIA) were included in this study who needed the diagnosis work-up of fever-of-unknown origin. The diagnosis of s-JIA and p-JIA was done to meet the ILAR criteria (2004). After fasting for at least 6 hours, whole body PET-scans were acquired 60 minutes after intravenous injection of 3 – 5 MBq/kg ¹⁸F-FDG. The interpretation of ¹⁸F-FDG uptake was based on visual characteristics.

Results:

¹⁸F-FDG uptake in shoulder joint areas was found in 42 out of 57 patients with s-JIA (74%) and in 5 out of 11 patients with p-JIA (45%). ¹⁸F-FDG uptake in knee joint areas was demonstrated in 19 patients with s-JIA (33%) and 7 patients with p-JIA (64%). Although in patients with s-JIA ¹⁸F-FDG uptake was found in shoulder areas, physical examination failed to reveal inflammatory symptoms/signs around shoulders. Additionally, two types of PET images were outstanding in s-JIA; one was ¹⁸F-FDG uptake in red bone marrow such as the spine, femur heads, and pelvis as well as spleen (11 cases), and other type was the uptake in the major joints such as hips, elbows, wrists, knees, and ankles (7 cases). The former findings were correlated with elevated levels of inflammatory markers (WBC, ESR, and ferritin) while the latter were with significantly increased levels of MMP-3 (P<0.05).

Conclusion:

There was a noticeable accumulation of ¹⁸F-FDG uptake in bone marrow of s-JIA patients which may indicate the inflammatory focus of this disease and play an important role in the pathogenic basis of arthritides and systemic inflammation of s-JIA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/positron-emission-tomography-assessment-of-children-with-systemic-onset-juvenile-idiopathic-arthritis/