FDG-PET in macrophage activation syndrome associated with systemic juvenile idiopathic arthritis

Area of Science:

• Nuclear Medicine
• Pediatric Rheumatology
• Hematology

Background:

• Systemic juvenile idiopathic arthritis (s-JIA) can lead to macrophage activation syndrome (MAS), a life-threatening condition.
• Diagnostic challenges exist for s-JIA-associated MAS, particularly differentiating it from other severe conditions like acute leukemia.
• 18F fluorodeoxyglucose positron emission tomography (FDG-PET) is a valuable imaging modality in various inflammatory and neoplastic conditions.

Observation:

• A case of s-JIA-associated MAS presented with a distinct FDG-PET finding: greater splenic than hepatic FDG accumulation.
• This specific FDG uptake pattern was also noted in patients with acute leukemia, highlighting a potential diagnostic overlap.
• Serum interleukin-18 (IL-18) levels were markedly elevated (255,000 pg/mL) in the patient with s-JIA-associated MAS, contrasting with milder elevations (360-1480 pg/mL) in leukemia patients.

Findings:

• The observed FDG-PET pattern, while characteristic, is not pathognomonic for s-JIA-associated MAS and can be seen in acute leukemia.
• Extremely elevated serum IL-18 levels were a key differentiator in this s-JIA-associated MAS case.
• The combination of FDG-PET imaging and serum IL-18 measurement appears promising for distinguishing s-JIA-associated MAS from acute leukemia.

Implications:

• FDG-PET may serve as a useful indicator for identifying patients with s-JIA and MAS presenting with fever of unknown origin.
• Integrating FDG-PET findings with serum IL-18 levels could improve diagnostic accuracy for s-JIA-associated MAS.
• This combined approach may aid in timely and appropriate management of complex pediatric rheumatologic and hematologic conditions.